AL TEXT-B jy i \ SERIES N. SMITH tfttUUMUtrUHCUantf^^^r'-r-^f*-- BAIL/E \{\\i Glass -£ /O 1 'alt. METERS 500 400 300 200 100 .r METSnS soo ■400 300 zoo iOO c \ \e \ V \ \ \ \ \, ) \ ^ \ / \ 'N \ o^ y i^ f V. Fig. 3. — Examples of different states of air equilibrium: AB, adiabatic gradient for dry air (neutral equilibrium) ; CD, temperature inversion (stable equilibrium), and EF, superadiabatic gradient (unstable equilibrium). range in temperature is much less than in the interior of the country or on the Atlantic coast. 22. Adiabatic change in temperature. — Ascending air ex- pands and descending air is compressed because of the chang- ing pressure (see paragraph 10). When air is compressed work is done on it and its temperature is raised, when it ex- pands it does work and it is cooled. Whenever changes in pressure and volume of any gaseous matter occur without heat being added or subtracted from it, there will be a partic- ular rate of change of the temperature, depending on the nature of the gas. The rate of change is then called the adia- INTRODUCTORY METEOROLOGY batic rate. In the case of unsaturated air, the adiabatic rate of change of temperature amounts to 1.6° F. for each 300 feet variation in elevation, or, more ac- curately, 1° C, for each 103 meters. The line AB in Fig. 3 illustrates the adiabatic gradient for dry air. 23. The average vertical temperature gradient or rate of temperature change upward does not differ much during summer from the adiabatic gradient but does considerably in winter. When the Fig. 4. — Maximum (lower) and minimum (upper) thermometers. Instead of being set as in this il- lustration the minimum thermometer must be set level and the maximum thermometer with the bulb end slightly ele- vated, as is shown in Fig. 5. Fig. 5. — Thermometers properly mounted in a lattice-work shelter. The 8-inch rain-gage is shown set up in its shipping box at the right. (See Fig. 9.) surface of the ground and the air near it are warmed by bright sunshine, the line EF represents the gradient. The line CD represents the temperature variation under 8 AGRICULTURAL METEOROLOGY conditions of temperature inversion as explained in para- graph 17. 24. Recording the temperature. — The ordinary ther- mometer is well known. Fig. 4 illustrates the self-registering maximum and minimum thermometers and Fig. 5 these ther- moneters mounted in the louevered shelter in most common use. Thermometers must be exposed in the shade and so as to have good air ventilation. Fig. 6 shows a good type of self recording thermometer, or thermograph. 25. Temperature records. — Maximum and minimum temperatures are important factors in crop development, as plants may be damaged by a few hours of excessive heat or killed by a brief period of freezing weather. The mean daily temperature is obtained approximately by adding the high- est and lowest temperature values together and dividing by 2. Similarly the mean monthly temperature may be ap- proximated by dividing the sum of the daily '^means'' by the number of days in the month. 26. Mean temperature and vegetation. — Mean monthly temperature figures are usually given in climatological tables, but weekly or ten-day means are of more value in studying Fig. 6.— Richards thermograph, the relation between tempera- or self-recording thermometer, ture and plant growth.^ Mean maximum and mean minimum temperatures are often of more importance in vegetation than the mean daily temperatures because they represent more clearly the actual temperatures that plants experience. PRECIPITATION Dove has said: ''The atmosphere is a vast still, of which the sun is the furnace, and the sea the boiler, while the cool air of the upper atmosphere and of the temperate zones plays the part of condenser, and we on a wet day catch some of the liquid which distils over." 27. Moisture in the atmosphere. — Water-vapor is one of the most important constituents of the atmosphere. It is essential to animal and vegetable life, and yet on a cold win- INTRODUCTORY METEOROLOGY 9 ter day it may not comprise more than .001 part of the at- mosphere, and its maximum on a warm summer day near the seashore is never more than about .05 of the atmosphere. 28. Depends on the temperature. — The temperature de- termines the amount of invisible moisture that can be present in the atmosphere as is shown by the following, giving the weight of water vapor in the atmosphere when completely saturated : Weight of a cubic foot Temperature of saturated vapor. degrees F. Grains troy 100 19.766 80 10.933 60 5.744 40 2.849 20 1.235 0.481 -10 0.285 -20 0.166 -40 0.050 This indicates that at a temperature of 40° it is not possible for the air to contain more than one-half as much water- vapor as it can at 60°. Almost one-half of the total water- vapor in the whole envelope of air that surrounds the earth is within one mile of the earth's surface, while one-half of the atmosphere is above three and one-third miles. At a height of six miles above the surface of the earth, where the temperature is about 60° below zero, the total amount of water-vapor is only one ten-thousandth of the atmosphere. 29. Evaporation. — The process by which a liquid becomes a gas or vapor is termed evaporation. The rate of evapor- ation or the rapidity of the escape of the molecules from the water surface into the atmosphere in the form of vapor de- pends on the temperature, wind velocity, dryness of the air, and to a slight extent the pressure. 30. Humidity. — The amount of water-vapor present in the atmosphere is called the absolute humidity, and it may be expressed in the weight of the vapor in a unit volume, or in the expansive force that the vapor exerts termed va- por pressure. The absolute humidity usually varies with the temperature. 10 AGRICULTURAL METEOROLOGY 31. Relative humidity. — The absolute humidity divided by the saturation humidity at the same temperature is called the relative humidity. It- is expressed in percentages. The diurnal relative humidity curve varies inversely as the temperature. 32. Saturation. — When the water-vapor present in the air is one-half as much as possible at the temperature, the relative humidity is said to be 50 per cent. When three- fourths, the relative humidity is 75 per cent. When the relative humidity is 100 per cent, the air is said to be com- pletely saturated. A room 20 x 20 feet and 10 feet high contains 4,000 cubic feet of air. If this air were completely saturated at a tem- perature of 80°, there would be 3 quarts of water in the at- mosphere in an invisible form. If the tem- (Iw^ perature should be 60°, only 3 pints of water i^^=rii could be held in suspension in the atmos- I im phere of the room. If the temperature of I 1^ the air should be zero, it could contain less I w| than 0.3 of a pint of water. II |[Bk 33. Dew-point. — The dew-point is the it MS temperature of saturation for the moisture IJl mH present. During the warmest part of the III ^^ (Jay, while the actual amount of moisture in the atmosphere is usually large, the amount is seldom sufficient for saturation, and the relative humidity is generally low. As the temperature falls in the late afternoon, the capacity for moisture decreases, hence the relative humidity increases. When satura- tion is reached, the temperature is at the dew-point. Any further cooling will cause part of the moisture to condense in the form of dew, fog, frost, or cloud. The difference between the temperature of the air and the dew-point temperature is called the com- plement or depression of the dew-point. 34. Measuring the moisture in the at- mosphere. — The sling-psychrometer or whirled psychrometer is used to determine the dry and wet bulb temperatures (see Fig. 7). From these data and simple hygrometric tables, the F I G. 7. — S ling psychrometer. INTRODUCTORY METEOROLOGY 11 absolute and relative humidity and dew-point temperature can easily be determined. 35. Condensation. — The natural processes of the con- densation of the water-vapor in the atmosphere into visible form depend on a decrease in temperature. If the tempera- ture of the air in a room is at 80° and if the space is completely saturated, about one-half of the moisture would be forced to condense if the temperature should be lowered to 60°. The condensation of the moisture would take place upon the cloth- ing and other objects in the room which might be cold. The sweating of ice pitchers is a well known example of the con- densation of moisture upon any object the temperature of which is below the dew-point. 36. How clouds are formed. — The temperature of the air is cooled sufficiently to cause the condensation of the sur- plus moisture into fog or cloud: (1) by expansional or dy- namic cooling due usually to vertical convection; (2) by contact cooling; (3) by the mixture of masses of air of un- equal temperatures; (4) by radiation. 37. Cloud types. — There are three main cloud types. (1) Cirrus, very high fibrous, white clouds that are composed of ice particles (see Plate I). (2) Stratus, a low, fog-like cloud of wide extent. From the top of high elevations these clouds have the appearance of valley fogs (Plate II). (3) Cumulus, a flat-bottomed cloud with rounded top (Plate III). The cumulus is a typical fair weather cloud, but will fre- quently grow into the cumulo-nimbus or thunder head, as shown by Plate IV. There are many combinations of these cloud types some of which are very beautiful. A nimbus is any cloud from which rain is falling. This is frequently classified as a fourth cloud type. 38. What makes it rain. — Rain is caused whenever a large mass of air is cooled below its dew-point or tempera- ture of complete saturation. Clouds are formed just as soon as the dew-point is passed and condensation into visible drops begins to take place. If the cooling continues, large drops will be formed from the smaller cloud particles and these drops will fall to the earth as rain. Vigorous cooling in masses of air of sufficient quantity to cause any considerable amount of precipitation is brought about only when the air is cooled by expansion. Wlien a 12 AGRICULTURAL METEOROLOGY mass of air is carried to higher altitudes by any cause it ex- pands, because there is less air above it and the presure on it is less and this act of expansion reduces its temperature. The rate at which it cools, before it reaches the tempera- ture of complete saturation, is 1° F. for every 188 feet. After condensation begins, the rate of cooling is considerably less. If a current of air with a temperature of 80° and a relative humidity of 75 per cent is forced up to ten times 188 feet, or but little more than one-third of a mile, some of the moisture must be condensed into clouds and rain. Ascending air is cooling and is then apt to be cloudy and rainy; descending currents of air are warming, the capacity for moisture is increasing instead of decreasing, and they are most likely to be accompanied by clear skies. 39. Rainfall increases with elevation on the windward side of mountains. — Currents of air blowing over a range of mountains are being cooled by expansion at the adiabatic rate, and the temperature is decreasing, hence there will be an increase in the rainfall up to a certain level, depending on the topography, and the like. The maximum level is about 5,000 feet in the western mountains, but it varies in different places. Precipitation decreases with higher elevations on the windward side, and then decreases with decreasing elevation on the leaward side, as the air there is being warmed by compression. 40. Measuring rainfall. — Fig. 8 shows one type of self-recording rain-gage, while Fig. 9 illustrates the ordinary rain-gage with a cross-section to show the different parts. The receiver of the standard (United States) is 8 inches in diameter, while the area of the inner tube is one- tenth of that of the catching surface. The amount of fall is measured, on a scale of 1 to 10, with an ordinary rule. That is, 1 inch of water in the gage is 0.10 inches on the surface of the land, and so on. Amounts less than 0.01 inch (0.1 on the rule) are re- corded as ''T" (trace), an amount too small to be measured. 41. Rainfall data. — Rainfalls are tabulated by daily, Fig. 8.— Self-record- ing, tipping bucket rain-gage. INTRODUCTORY METEOROLOGY 13 monthly, seasonal, and annual amounts, and long-period averages of these. The National Weather and Crop Bulle- tin published by the Weather Bureau shows weekly rainfall charts or tables. From an agricultural point of view, all pre- Frant Viexv. VerticaZ SecUaru HortzomixH S>ectzaw,E-F. O f i 3 4 S 6 7 8 9/0 // /2_J3 /4IS '617/ 8 ^3 £0 21 2223 ; 1/ \ \ */ ; \ 1 1 h ••• i b 1 A \ / T "^ : / U\ / v \ i ^i \ P f: ." ] \ r / / v V 1: L 1: \ /■ \ 1 \ • ' 1 / — 1~ 1 ^ h '. •. : 1 C -\ ^ ! \ . '. 1 '. ; \ 1 • > \ \ ,^ S Fig. 11. -Relation of weather to the yield of potatoes in Ohio, 1883-1909. can be made, with three or more curves there seems to be only a confusion of lines. While this method can be used to show roughly the rela- tion between two factors, it is not recommended for careful work, and not at all when three factors are involved, because of the confusion of lines. 100. A better method. — If three curves are to be used, it is far better to arrange the years so that one of the factors will have an increasing or decreasing value, as in Fig. 12. In this chart the years are arranged so that the curve showing the yield of potatoes runs from the highest yield regularly to the lowest. Then, by drawing the other curves for the years 36 AGRICULTURAL METEOROLOGY as shown at the top, broad general correlations can be shown. It will be found better in practice, however, to put only two curves on the same diagram. Examination of the curves on this chart indicates a slight general relation between the yield and rainfall, and a strong opposite relation between the yield and temperature. When 1906 1883 1891 1904. 1909 1902 1896 1903 1888 1886 1905 1908 1900 1907 1884 1885 1889 1899 1894 1895 1898 1892 1893 1901 1890, 1897 1887 1 1 Q 1 K^ +4.5 +4.50 44.0 +400+40 + 35 +3.50 +J5k *3.0 ^3.00+30 +2.5 ^2.50 +25 +2 ^2.00+20 +/5 */.50+/5 */.0 W.00+/0 +0.5 W.50 + 5'^ A/OPMAL -as -0.50 -j-C -/.o -/.oo -/o- -/.5-/.50-/5 -2.0-200-20 -25 -2.50 -25 -3.0 -300 -JO -3.5 -3.50-35 -4.00-40 -45 • ^ / 1 I I \ 1 1 C \ 1 - "^ 1 ; •. ; r k . ; s A \ ... '. : ■• '•. .' / i\ 1 \ : *. i '. r' I / f t^ 'C •■h- 4, ; , 'f \ / .•• . / y TT T •• •/ ^ *• •1 ■\r . \ •' : V /•• i 1 1 / ^ \ 1 \ ; "• V.J ^• 1 ; ; \ _ *^ 1 1 \ \ \ ^ \ \ / r \. B ' \ / s > V f— ,^ \ A L ^ -£. ' Fig. 12. — Relation of rainfall and temperature to the yield of potatoes in Ohio, 1883-1909. the yield is above the normal, the temperature is nearly al- ways below normal, and when the yield is low the tempera- ture is generally high. 101. Proper way to find the relation between two vari- ables. — In all attempts to ascertain the relation between two variables, such as rainfall or temperature and crop yield, three steps are necessary: (1) Plot the data as in Figs. 13 to 17; (2) proceed to find the equation of the data on the chart by the method of least squares and trace the calculated straight line or curve of nearest fit; (3) if it is found that the relation between the two variables can be represented by a CORRELATION 37 straight line quite as well as by a curve, the correlation coeffi- cient may be calculated. In this case it is not necessary to make the calculation under No. 2. 102. The dot chart the first step. — In all attempts to ascertain the relation between two variables, it is practically indispensable to make the easily-constructed dot chart, as shown in Figs. 13-17. The data for Fig. 13 were taken from Table 1 showing the average July rainfall and average corn yield in Ohio from 1854 to 1913. Table 1. — Average July Rainfall and the Yield of Corn in Ohio, 1854 to 1913 Rainfall, Yield, Rainfall, Yield, Year inches bushels Year inches bushels 1854 2.6 26.0 1884 3.8 33.3 1855 5.8 39.7 1885 3.2 36.8 1856 2.6 27.7 1886 2.9 33.5 1857 4.9 36.6 1887 2.2 30.5 1858 4.7 27.7 1888 4.4 38.9 1859 1.6 29.5 1889 4.2 32.3 1860 5.8 38.2 1890 2.0 24.6 1861 3.3 33.5 1891 3.8 35.6 1862 3.6 30.0 1892 3.8 33.3 1863 2.6 27.0 1893 2.5 29.1 1864 2.1 27.0 1894 1.6 32.6 1865 5.7 35.0 1895 2.0 33.7 1868 5.1 36.5 1896 8.1 41.7 1867 3.2 29.8 1897 4.6 34.3 1868 2.7 34.4 1898 4.0 37.4 1869 4.8 28.4 1899 4.2 38.1 1870 4.7 37.5 1900 4.6 42.6 1871 3.7 36.7 1901 2.7 30.0 1872 6.7 40.9 1902 4.7 38.8 1873 6.2 35.1 1903 3.7 31.5 1874 3.8 39.2 1904 4.1 32.8 1875 6.9 34.2 1905 3.9 37.9 1876 6.4 36.9 1906 5.1 42.2 1877 3.7 32.5 1907 5.4 34.8 1878 5.4 37.8 1908 4.1 36.1 1879 4.2 34.3 1909 3.8 38.7 1880 4.2 38.9 1910 3.2 36.6 1881 3.6 31.0 1911 2.4 38.6 1882 3.2 34.0 1912 5.7 42.8 1883 4.2 24.2 1913 5.2 37.8 38 AGRICULTURAL METEOROLOGY • • • • • • • • • • (•) • • • • • • • • • • < • •• • • • • AT r I- J 20 25 JO 35 40 45 50 y/£LD or CORA/ /A/ BU5HEL5 PER ACRE Fig. 13. — Dot chart showing the relation between the July rainfall and the yield of corn, Ohio, 1854-1913. 103. How dot chart is made. — A dot is placed on the chart for each year so that its location agrees with the rain- fall value and the yield figures for that year. For example, on Fig. 13, in 1913, the rainfall averaged 5.2 inches, while the yield of corn was 37.8 bushels to the acre, hence the dot (in- closed in brackets) was located to agree with these values. CORRELATION 39 79 78 77 • • • • 76 < K • • • ^75 • • 74 K |- • • « • • A/OffMAL • • • •- ,% • • * • • • • • • 7/ • • •• 70 69 • i AT 30 40 60 60 70 80 90 /OO W Y/£-LD or POTATOES /Af BU5M£LJ P€ff ACRE Fig. 14. — Dot chart showing the relation between the mean tempera- ture in July and the yield of potatoes, Ohio, 1860-1914. 40 AGRICULTURAL METEOROLOGY 104. Potato yield and temperature. — Figs. 14 and 15 were prepared in a similar manner from data giving the mean temperature for July and the yield of potatoes in Ohio and Portage County, respectively.' 105. No relation shown in Fig. 15. — When the dots are promiscuously scattered over the chart, as in Fig. 15, there is no relation between the factors and no further time need be spent on their consideration. In other words, Fig. 15 shows that the mean temperature for July has no dominating effect • o • • •• •• • o • • ••• • AT SO 60 70 80 90 lOO /lO /20 IJO Y/ELO or PoraTOEs in bushels per acre Fig. 15. — Dot chart showing the relation between the mean tempera- ture in July and the yield of potatoes in Portage County, Ohio, 1884- 1913. on the yield of potatoes in Portage County, Ohio. (See Chap- ters VII, VIII, and IX for further discussion of this matter.) 106. A negative relation in Fig. 14. — Fig. 14, however, shows clearly that in general a warm July is unfavorable for potatoes in the state of Ohio as a whole, and that a cool July is usually followed by a yield of potatoes above the normal. The lines in the center of the chart indicate normal tempera- ture and yield values. 107. Fig. 13 indicates a positive relation. — When the dots are grouped as in Fig. 13, a positive relation is indicated. In this particular case, the chart shows that the heavier the rain- CORRELATION 41 fall in July in Ohio, the greater the corn yield will be, in gen- eral. Both figures will be discussed further in Chapter VIII. 108. When mathematical correlations should be made. — The dots in Figs. 13, 14 and 15 indicate not only that there is a relation between the two factors, but that this relation can be represented by a straight line. When the dots show a definite linear relation or a relation that can be represented by a curve, then the best fitting line or curve should be deter- mined. This is step No. 2, under paragraph 101, and gives the definite relation between the two variables. The for- mula can be used in calculating one from the other, such as yield from rainfall. 109. To determine the straight line of nearest fit. — The calculation of the straight line of nearest fit by the method of least squares will be illustrated by a method recently evolved by the author for predicting minimum temperatures on nights when radiation conditions prevail. The dot chart in Fig. 16 shows for San Diego, California, the relation be- tween the depression of the dew-point temperature from the air temperature in the late afternoon, and the variation of the minimum temperature during the following night from the evening dew-point, as indicated by the figures and legend on the chart. The line A, B, was calculated by the method of least squares, as shown by the following. 110. Equation for a straight line. — The equation for de- termining the straight line of nearest fit, such as A, B, in Fig. 16, is y = a+bR. In this^case R is the depression of the evening dew-point {i. e., the number of degrees that the dew-point is below the dry bulb or current temperature at the evening observation); y is the variation of the minimum temperature during the coming night from the evening dew- point, or the value that is desired in predicting the minimum temperature. The values a and b are unknown factors that are determined by Table 2 and the calculation following. 42 AGRICULTURAL METEOROLOGY y' / / / / • /.: "'/ /' y< / y * • * ; ' y ;-•■: ' /? = y=VA/ TEMP y = a + t>H = LINL Ati CSS'OA/ or THE DCW POff 9/AT/ON or THC MINIMUM \IT 'J- A' ERATURC F/^ POIN 10M T rne L ■IEVd, X would be negative. 252. Equation in Texas. — Kineer applied this equation to the weather conditions in Texas for the period from 18-94 to 1913, for the months of April to September, inclusive, with a resulting correlation coefficient of +0.88 and a probable error of only =b 0.03. The actual results are shown in Table 10. Table 10.- -comparison of actual with computed departures op Crops from Normal Yield Actual Computed Years departures " departures Lbs. acre Lbs. acre 1894 65 46 1895 — 19 -14 1896 -64 —64 1897 - 5 34 1898 42 47 1899 15 8 1900 56 - 9 1901 — 11 — 6 1902 -22 -20 1903 — 27 -29 1904 13 13 1905 - 6 -10 1906 55 54 1907 -40 —44 1908 26 24 1909 — 45 -48 1910 -25 -36 1911 16 5 1912 36 30 1913 -14 -6 253. General weather effects. — Cotton has the cliarac- teristics of a weed and due to this fact and also owing to the long season during which growth and fruiting take place, there seems to be no comparatively short period in the devel- opment of the crop in which unfavorable weather is likely to prove disastrous. . Whenever unfavorable weather prevails, the plant does not necessarily suffer permanent injury, but 116 AGRICULTURAL METEOROLOGY improves rapidly with the return of good growing weather even after a long period of adverse conditions. 254. Seasonal weather. — There are certain well-defined weather conditions, however, which hinder or promote growth. Rainy and cold weather early in the season hinders the preparation of the soil and the planting of the seed or proper germination; excessive rainfall in the first part of the season not only prevents proper cultivation, but encour- ages shallow root development; dry and hot weather later in the season is very detrimental. 255. April should be warm and moderately dry especially in the central and eastern part of the belt, as cold and wet weather hinders planting and cultivation, and may make the crop so late that it is liable to receive frost damage in the fall. In Texas, however, low yields have been more frequent with a dry April than an April with the rainfall above the normal. Cool Aprils in this state are followed by more low yields than high ones. Kincer found that of fourteen years with com- paratively low cotton yield in Texas, nine of them had the average temperature for the state for April below the normal and five above normal. 256. May. — In the central and eastern states. May should be warm and comparatively dry, as cool and wet weather retards growth and final maturity and prevents proper cultivation. 257. June. — Cool and wet weather is harmful in June also as thorough cultivation is especially important owing to the length of time between the final chopping out period and the maturity of the last fruit, and the resulting tendency of the fields to become grassy. Kincer found that in Alabama the rainfall was above the normal from May 1 to June 30 in ten of the years from 1900 to 1915 and in seven of these years the yield of cotton was be- low the average. The rainfall was above the normal in Georgia in May and June also and in these ten years the yield was below the average nine times. In Alabama of eleven years in which the temperature was below the normal in May and June, seven had yields below the average and four above, while for the eleven years in Georgia with cool weather during these two months nine had yields below the average and two above the average. WEATHER AND CROPS 117 258. July and August. — Subnormal rainfall during the months of July and August is more frequently harmful in the western portion of the belt than in the central and eastern parts, owing to the normally greater amounts received in the latter districts. In general, the yield of cotton is largely af- fected by the rainfall during the months of July and August, 7 6 • • { • • • • • • •• • • • •• o • / • • ^ • • • iti °/C 70 12 S It n '5 2L :o 2. ?5 2. SO 2. 75 30 Fig. 29. — Relation between the rainfall in August and the yield of cotton in Texas, 1891-1918. especially the latter, but in the central and eastern parts of the belt temperature and moisture conditions during the early period of growth are of scarcely less importance. The influence of August rainfall in general, and especially in the western part of the belt, and the detrimental effect of cool and wet weather during the early growing season are indi- cated by the following. 259. Rainfall in July and August not the controlling fac- tor in Texas. — That the rainfall for neither August nor for 118 AGRICULTURAL METEOROLOGY July and August combined are the controlling factors in the cotton yield in Texas is shown by Figs. 29 and 30. While there is a general increase in yield with an increase in rain- fall, the relation is only approximate and no good estimate of the yield can be obtained from a knowledge of the rainfall. /2 ? B / A* /. • > • o / • MEAN ••• / •• • ' • / • • • / > • • a- 118 b' 10.13 y-a-hbr A' / i M.T. 'WO 125 150 175 200 225 250 YIELD OF COTTON- POUNDS 275 300 Fig. 30. — Relation between the rainfall for July and August combined and the yield of cotton in Texas, 1891-1918. ' 260. Winter rainfall and the yield of cotton in Texas. — The opinion is often expressed that the yield of cotton in Texas is largely dependent on the rainfall during the previous fall or winter. This belief seems to be disproved by Figs. 31 and 32. These charts indicate that small cotton yields are about as frequent with heavy as with light autumn or winter rain- falls. Also that heavy yields frequently occur with light win- ter precipitation, due to favorable weather in the spring and summer. 261. Some important comparisons. — For the sixteen- year period from 1900 to 1915, inclusive, the rainfall for August in Texas was normal or above seven times, and for these seven years the acre yield of cotton was above the six- WEATHER AND CROPS 119 teen-year average six times and below the average but once. For the nine years in which the August rainfall was below the normal, the yield was also below the average eight times and above the average once. For the same period in Alabama, the August rainfall was above the normal seven times, for which years the yield was above the average five times and /4.0 %'"' ^ %8. o 1^. / • • • • < 1 • MEAN < • • • • • • • • • : • • • a- 168.345 i?' 0.3334 y^a+br • J W.7. JOO 125 150 175 200 225 250 275 300 YIELD OF COTTON -P0UND5 Fig. 31. — Relation between the rainfall from October to December and the yield of cotton in Texas during the following year, 1892-1918. below the average twice, while for the nine years with sub- normal August rainfall the yield was below the average seven times and above twice. In Georgia, however, this period had six years with August rainfall above normal, four of which had yields below the average and two above the average, but for the ten years with subnormal August rainfall the yield was below the average seven times and above the average three times. After the plants have attained their vegetative growth, 120 AGRICULTURAL METEOROLOGY the ripening of the fruit and seeds is favored by cooler nights. 262. September and October. — The cotton is Hable to be beaten out and damaged by stormy weather after open- ing and while picking is going on. The amount of rainfall during the latter part of the growing season, particularly in /6 14 12 10 /9.d9 / • • •• • 1 • • • MEAN \. '1 • 8 6 4 2 " / • • • • ••/ • O ' . / • / a ^145. 4 ya+br ^ i /oo 125 J50 175 200 225 250 YIELD OF COTTON - POUNDS •275 300 Fig. 32. — Relation between the rainfall from November to March and the yield of cotton in Texas the following fall, 1892-1918. September, is also of special significance, as this largely de- termines the amount of the top crop, which plays a consider- able part in the total yield. A late fall with a delay in the first killing frost date also allows for the development of the top crop when not affected by weevil. 263. The weather effects of two seasons compared. — The Weather Bureau publishes diagrams each year in the Na- WEATHER AND CROPS 121 tional Weather and Crop Bulletin indicating the combined effect of rainfall and temperature variations on the growth and condition of several of the most important crops. Figs. 33 and 34 are taken from these diagrams and show the effect of two quite different seasons on the condition of cotton in Oklahoma. Fig. 33 is for 1917, which was generally favor- able for cotton, and Fig. 34 for 1918 when a severe drought prevailed in the western cotton states. In 1917 May was very cold and cotton was unfavorably affected, but with more No. 1. Oklahoma. 1 120 115 110 106 (100 90 85 80 75 M 1 .mill i4 lit ttttiii.iB 1 "^ ""^ 1 li •g 2.4 .3 2.2 d 2.0 "" — i ;■« ;& 1.6 R 1 1 1.0 - 0.8 - ■^: fc r — ~ 1=1 t - — 0.6 - 0.4 - 1 T 1 t T — f 7t 1 r f t ^ 1 1 1 i B 1 1 n ll 1 t 1 B JL *i 4.«S TV ™ § t^ ^ ^ 1 +^ -i- , > 1 H- 40 -r f^ ' ' S /'< h ST /i /\ f ^^ z. § to r \ J V/ ^ - v> \J ■^1 g - 2C' V \ / V ( I-*' '' V i "go \ i \j ^ To i\ f a -8° J \/ Fig. 33. — Diagram showing the effect of the weather on the condition of cotton in Oklahoma in 1917. favorable weather later there was an improvement in all of the states except Texas, and the earlier handicap was almost overcome. The generous rainfall in August in Oklahoma as shown by Fig. 33 was especially beneficial to this crop. In 1918 the weather during the spring was much more favorable, but drought and high temperature during most of the summer nearly ruined the crop in Oklahoma and Texas. The effect of these conditions in Oklahoma is especially shown in Fig. 34. During these months wet weather reduced the outlook for cotton in the eastern part of the area. 122 AGRICULTURAL METEOROLOGY 264. Insect pests. — ^Wet and cloudy weather favors the development of the boll-weevil, especially if wet enough to No. 1. Oklahoma. u HI 1 II 1 1 II 1 1 1 1 1 1 1 1 1 1 1 1 1 i 2.6 •g 2.4 .3 2.2 a 2.0 3 1.6 Si L4 1 1.2 £ l.n 0.8 0.6 0.4 0.2 £ 4-8° I + 6o 1 +40 » -f 2° 1 S -2° ■3-40 1-6° ^ -10° — _.. -- — -- - . •3 % h t ^ ^ 1 . ~\ - -| .__ J - — 1 ■ B B R i 1 H ■ \i i 1 K i 1 ■ 1 fli . ^N , y\ ^ /.- B V N''\ /i r- ^ , \ "^ ^ ^ i-'K / \ / - 90 / \ U u J£ t / N u \ Fig. 34. — Diagram showing the effect of the weather on the condition of cotton in Oklahoma in 1918. In the upper part of each of the diagram.s (Figs. 33 and 34) the heavy soHd line indicates the normal weekly rainfall, while the average for the state for each week is shown by the heavy upright line. The rainfall values are indicated by the figures at the left. In the lower part of each diagram the heavy horizontal line represents the normal temperature, while the variable black line shows the temperature for each week from the normal, as indicated by the figures at the left. The condition of cotton on the 25th of the month, as compared with a ten-year average, expressed in percentages as shown by figures at the right, is indicated by the dots, and these are connected by broken lines. hinder cultivation; while in the eastern part of the belt, hot dry weather hastens the development of red-spider. 265. Boll-weevil and temperature. — With a mean monthly temperature of 60°, the activities of the weevil are greatly reduced. Investigations by the Bureau of Entomol- ogy, United States Department of Agriculture, show that an WEATHER AND CROPS 123 exposure to a temperature of 20° for a period of six hours is fatal to the boll-weevil. It is probable, therefore, that when- ever the winter temperature reaches a minimum of 10°, the weevil will be greatly reduced in all districts and almost en- tirely killed out in prairie sections, where there is less protec- tion than m wooded areas. If only a few escape death how- ever, they may multiply so rapidly with favorable weather in the spring and summer as to cause great damage, although the damage will be later than if the winter is mild. The following statement by L. O. Howard is of interest in this connection: The most important climatic factors which affect the boll-weevil are wmter temperatures and spring precipitation. Naturally low winter temperatures reduce the weevils enormously in numbers, while high sprmg and early summer precipitation has the effect of increasing their numbers. It has been found in observations made during several sea- sons that no accurate forecast of weevil conditions during the summer can be made from winter mortality. Attempts to do this were made in the early days of the mvestigation of the weevil, but we have been forced to abandon further attempts. On several occasions the weevil has been decimated by low winter temperatures but wet weather the following May and June negatived the conclusion of summer scarcity which would appear to be warranted by the winter conditions. In a similar way the survival of an enormous number of the weevils through mild winters has not resulted in any proportionate damage of the crop, on account of dry weather during May and June. 266. Boll-weevil and rainfall.— The most important single factor in holding the weevil in check is dry weather dur- ing the growing season, as dryness increases the death rate of immature weevil in the fallen squares enormously. 267. Wind and spread of weevil.— The normal advance of the boll-weevil into new territory is 50 miles a year, but high winds, with other conditions favorable, may cause a much more rapid spread of this insect, as was the case from August 15 to 31 in 1915 when they advanced fully 100 miles. Flax Flax for fiber is grown in regions in Europe with high hu- midity, moderate rainfall, and rather cool and uniform sum- mer temperatures, as even and rather slow growth is neces- sary to produce a long, even, fine fiber. Anything that checks 124 AGRICULTURAL METEOROLOGY the steady growth of straw during the period preceding boll formation is sure to result in an inferior type of fiber. In Egypt, the beginning of flax-culture dates back to 4000 B. C. 268. In North America. — Flax is grown mostly for seed in this covuitry and principally in the Dakotas and Min- nesota and the adjoining Canadian provinces. In this sec- tion of the United States, the annual rainfall is 15 to 20 inches and the rainfall during its growing season of 80 to 110 days is from 10 to 12 inches. As this is a region of rapid tem- perature changes and uneven rainfall, the straw is short and coarse and the fiber is uneven, hence only seed is produced. For the best development for seed also a steady even growth is desirable with only sufficient moisture to cause a sturdy type of stem growth and a heavy production of foliage. Very recently the cultivation of fiber flax is becoming an established industry in eastern Michigan and the Willamette Valley in Oregon. 269. Moisture and flax. — Too much moisture results in a weak and imperfect stem and poor boll and seed formation. A severe drought near the time of flowering or boll formation will cause a hardening and ripening of the straw, especially of the slender stems on which the bolls form, thus cutting off the proper supply of food materials. Hot dry winds and a lack of moisture when the plants are in bloom are detrimental to the seed crop, while cool and cloudy weather causes it to bloom for a long time and hence to ripen unevenly. Cool nights, fairly warm days, with plenty of moisture are conducive to extensive branching. 270. Frost effects. — A shght frost after flax has reached a height of 2 inches may not injure the plant, but if it is cut off by frost at a point below the first or "seed" leaves, the plant loses its power of growth. 271. Flax in North Dakota. — Warm weather with some- what less than the normal rainfall during May and June, while planting and germinating are going on, produces the best condition for flax in North Dakota. The best results have been obtained with wet and warm weather in August, and wet and cool in early September. The maturing period falls in August and the first of September so it is necessary to have plenty of moisture to fill out the seed well. The seeding of flax is mostly done in this state during the WEATHER AND CROPS 125 last half of May and the first half of June, although seeding may be continued until the middle of July. The crop is har- vested in the latter part of August, September, and the first part of October. Hemp Hemp is cultivated in warm countries for the production of a narcotic drug, but in moist temperate climates such as the central part of the United States it is cultivated for fiber. It is one of the oldest fiber-producing crops, and is important in Japan, China, and India. 272. In the United States. — The principal hemp-produc- ing districts in the United States are in central Kentucky and in parts of Wisconsin. Practically all the hemp seed in the United States is produced on narrow strips of land between the bluffs, along the Kentucky River. 273. Growing season. — In fiber production, the seed is planted about the 10th of April in Kentucky and the growing season is about 130 days. For seed, it is planted somewhat earlier and harvested in the first part of October. 274. Temperature. — Hemp grows best where the tem- perature ranges between 60° and 80°, but it will endure higher or lower temperatures. Light frosts will not greatly injure either the young or mature plants for fiber, but a frost before harvest will greatly damage the plants for seed. 275. Rainfall. — The most critical period of growth is shortly after it comes up, when it must have plenty of mois- ture, as a period of dry weather at this stage may cause great injury. FRUITS The climate should be carefully considered in the growing of fruit. The prevailing weather also influences the yield to a marked extent. The fruits will be discussed separately. Almonds (These nuts are classed with fruit in California.) Almonds are the first of the deciduous fruit-trees to start to grow and to bloom in the spring and the last to lose their leaves in the fall. Its period of dormancy in this climate is very short, usu- ally being complete only during December and January. 126 AGRICULTURAL METEOROLOGY 276. Temperature and almonds. — The almond tree is hardy and will endure fully as much cold as the hardiest peach without injury. The blossoms on the other hand are very tender, and even when there is an entire absence of frost dur- ing blooming, sudden marked changes in temperature may greatly damage or ruin the crop. The most tender stage in the blossoming and development of the young fruit seems to be that immediately following the dropping of the calyx-lobes as the fruit first commences to swell rapidly. 277. Moisture and almonds. — Continued rainy, damp, and cold weather at the time of blooming is likely to sour the pollen or actually wash it away. Foggy or moist weather dur- ing ripening or harvesting is very objectionable. Ayjples In the eastern part of the United States, the area of exten- sive apple-culture does not extend south of the mean summer isotherm of 79°, or north of the mean winter isotherm of 13°. There are few orchards in the Great Plains states west of the 18-inch annual precipitation line. The leading apple states are New York, Michigan, Pennsylvania, and Missouri. 278. Weather and apple yield. — A study of the effect of the weather of different months on the yield of apples was made for Belmont County, Ohio, covering the period from 1889 to 1910. This showed that the most important months were February, of the current year, and June of the previous year. 279. February. — In the twenty-one years, the apple crop was always below the normal when February was warm and wet and usually above the normal when it was cool and dry. The correlation coefficient between temperature and yield was — 0.51 and between the rainfall and yield, — 0.50, the probable error in each case being ±0.10. 280. March. — Wet weather in March was also detri- mental, especially if warm, and cool and dry weather was fa- vorable although these conditions were not so well marked as in February. 281. Other months. — No marked relation was shown between the yield and the weather in April, May, June, July, or September. August, however, should be warm and wet for best results. A comparison of the yield with the mean WE AT ITER AND CROPS 127 monthly temperature and precipitation of the previous year showed no relation with May or July conditions. It did show that dry weather in August was detrimental although a wet August was not always followed by a good jdeld. A cool and wet June, however, was always followed by a yield below the ^7 +2 "2 '4 -5 -5 — 1 Warm & Wet June Cool & Wet Feb. \CooJ & Wet June Warm & Wet Feb. _ __ PRB /*//5/ •ry\ -ri/^ti 1 - C/F//M 1 1 - • + ^ ^ 5i: 1 ■ 1 M Warm & Dry June \ ^ ^ 1 i i 1 Cool & Dry June '.Coc ?/ 8 \ Dr^ y /^ «.j J Wan m d ■On / ^ eb. AT t5 -tA V-J -^2 -tl '2 -J '4 -5 '6 -7 '8 Fig. 35. — Combined effect of the weather of June of the preceding year and February of the current year on the yield of apples, Belmont County, Ohio, 19 years. normal the next year while a dry and warm June usually pre- ceded a good crop the following year. 282. Fruit and leaf development. — As the fruit-buds de- velop in the preceding year and as wet weather favors active extension growth which is produced at the expense of fruit- bud formation, it follows that a dry and warm June should be favorable for the formation of a good number of fruit-buds 128 AGRICULTURAL METEOROLOGY for the next year's crop. A good rainfall in June produces a large amount of soil-moisture during succeeding weeks or months when the buds are developing, thus making a prepon- derance of extension growth and thus a larger percentage of branch and leaf-buds and a smaller percentage of fruit-buds. 283. Combined effect of June and February. — As a warm and dry June of the preceding year and a cool and dry Feb- ruary of the current year are both favorable for a good yield of apples, these conditions have been combined in Fig. 35. It should be noticed that in this chart the February tempera- ture values have been reversed so that a warm June is grouped with a cool February. When the rainfall for the two months combined was above the normal, the yield was always below normal, and when below the normal the yield was above the norinal eight times in ten. A correlation of the yield with the combined rainfall for June of the preceding year and Febru- ary of the current year gave a correlation coefficient of — 0.60 (probable error ±0.10), and with the average temperature (with the February temperature departures reversed) gives a correlation coefficient of -|-0.48, with a probable error of =t 0.11. 284. August and February combined. — In Fig. 36 the weather of August of the preceding year and February of the current year were combined in a similar manner. It must be noted that a dry August is combined with a wet February by reversing the values so that a wet February is grouped with a dry August. In the thirteen years when the departure of these combined rainfalls, after reversing the August values, was above the normal, the yield was below the normal every year but one. 285. Combined precipitation for June, August, and Feb- ruary. — On combining the departure of the precipitation for June of the preceding year and February of the current year above the normal with the rainfall for August of the pre- ceding year below the normal, the correlation with the yield gave a coefficient of — 0.62 with a probable error of =i=0.09. 286. Apple diseases. — Bitter-rot or ''ripe" rot of apples is a typical hot weather disease. It is serious in the more southern apple districts. Hot and wet weather with the pre- vailing temperature above 80° produces conditions favorable for its spread. A local shower on a hot July afternoon may supply just the right condition when the whole crop may be WEATHER AND CROPS 129 destroyed in a week. The outbreak may be checked by a few days of cool weather with the mean temperature below 70°. Special forecasts of weather conditions favorable for the spread of this disease should be made by the Weather Bureau and distributed as in connection with the apple-scab, so that spraying may be done at the proper time. 287. Codlin-moth.— Warm and dry weather favors the development and multiplication of this apple pest. The be- ♦5 ] 1 1 1 f Wet 3 VJarm Fet) Dry & Warm Aug \we/ '& Coo/ Feb Drq a Coo/ Aug 4-4 — +J --+- ♦P P/i£ ■ !;; CI PI TAT 10 + N — 1 • ■ -/ ■ * * 1 ' + * i1 -^ 1 ^ -J 1 -4 Wet S Warm Aug. Dry & Worm Feb. 1 Wet 'S Coo/ Aug Dry & Coo/ Fel?. AT •t- 9' - 7° -t- y +. f ^A +. r * ?• ■*■ ' aI y(^. - /• - ?' - r -' f - 5" -C i' - 7* -a Fig. 36.— Combined effect of the weather for August of the preceding year and February of the current year upon the yield of apples, Belmont County, Ohio, 19 years. ginning of emergence in the spring is hastened by high tem- perature in March, April, and May. In the state of Washing- ton it is known that the codlin-moth does not become active unless the temperature is 60° or higher. In other words, no breeding takes place when the temperature drops below 60°. Apricots 288. Apricots thrive best in the hot valleys of the South- west. The fruit ripens at a time of the year when the rela- tive humidity is at its lowest point and the danger of showers least, consequently the conditions are the most favorable for drying the fruit. They receive little injury from either the 130 AGRICULTURAL METEOROLOGY frosts of spring or the heat of summer, compared with apples or plums. Avocado or alligator-pears 289. This is a tropical or semi-tropical fruit. The fruit of the hard-shelled type requires over a year to mature. Some varieties will stand from 5° to 10° below freezing. Strong winds are often damaging. Cherries Cherry trees do not thrive as a rule in the southern states where the summers are long and hot. The southern limit is not quite so far south as that of apples. The northern limit of sour cherries approaches that of apples while sweet cher- ries are slightly less hardy, corresponding more nearly to the peach. The fruit-bud formation in some cherries begins about July 1, of the previous year, in central latitudes. 290. Weather and cherries. — Some preliminary studies in Ohio indicate that if February is wet it should be cool and if warm it should be dry for best results. April should be cool and wet. In May cool weather is more favorable than warm, and in June moderately dry weather is more favorable than wet. Currants and gooseberries 291. Both currants and gooseberries are natives of cool, moist northern climates and succeed best in the United States in the northern half of the country east of the 100th Meridian. They are injured by the long hot summers of the southern states, except in the higher altitudes of the Appalachian Mountains. Gooseberries are grown slightly farther south than currants. Both plants are very hardy and withstand extremely low temperatures, but as they blossom very early they are subject to frost damage. Cranberries Cranberries are indigenous to marshes, chiefly in the nor- thern states, although wild cranberries are found at consider- able elevations on moist mountain-sides in New England. Cranberries are cultivated intensively only in Massachusetts, New Jersey, and Wisconsin. WEATHER AND CROPS 131 292. Cranberries and temperature. — The vines are sub- ject to winter-killing and when water is available the cran- berry^ bogs are kept covered during the winter months. While frost is not often experienced in the summer months in the eastern states, it may occur during any month in the low- lying bogs in Wisconsin. The minimum temperature in the cranberry bogs may be from 5° to 15° lower than on the sur- rounding slightly higher ground. 293. Protection from frost. — Cranberries are protected from light frosts by raising the water in the ditches that run through the bogs, but the vines must be entirely covered by flooding to protect from severe frosts. Dates 294. Dates require intense summer heat and dry air, but will bear abundant crops only when well irrigated. The plants make their most rapid growth during the warmest part of the year. The dormant mature trees will endure an occa- sional temperature considerably below freezing, but there will be no development of the flowers or fruit when the tempera- ture is below 64°. Even a light rain after the fruit has begun to ripen is very damaging. The date harvest season in Cali- fornia is in September and October. Figs 295. Fig-growing is confined primarily to regions where the winters are comparatively mild. They are injured or killed to the ground by temperatures that do not affect most other fruits of the temperate zone when in a dormant condi- tion, especially when young. As the trees get older, they be- come less subject to winter-injury, and in Arizona are rarely injured by the cold of winter or the heat of summer. Grapes Grapes are raised in the United States principally in Cali- fornia, western New York, northern Ohio, and southwestern Michigan. Most of the raisins used in the United States are grown in the Fresno district of California. 296. Temperature and grapes. — Winter-killing of grapes can be traced to a lack of maturity in the fall. An index to 132 AGRICULTURAL METEOROLOGY this immaturity is the incomplete ripening of the crop as shown by high acidity and low content of solids, especially sugar. A warm rainy September and a cool cloudy October leave the vines soft and succulent and give poor conditions for proper ripening of fruit. If these conditions are followed by marked temperature variations during the winter, the crop of the next year is likely to be poor. 297. Critical temperatures. — When the vines are well matured, they will withstand a winter temperature of at least 25° below zero. It was found in New York that the danger point in the winter is between - 26° and — 30°. When in bud bloom, and setting fruit, the critical temperature is 31°. The leafing of some native varieties occurs after ten or twelve days with a daily mean temperature of 52° to 53°. If freezing weather follows, the leaves and young growth will be killed and although they will grow new vines the crop will usually be reduced. 298. Weather and grapes. — A study of the effect of weather on grapes in northern Ohio showed that for best re- sults, February and March should be dry and moderately cool, as wet and warm weather hastens growth and causes danger from later frosts. April should be moderately dry and warm as wet weather interferes with fertilization and anthrac- nose develops in cool and wet weather. May should be wet and warm to bring about vigorous growth. The grapes bloom in June in Ohio and a cold northeast wind or storm prevents pollination. Periods of warm sultry weather in June or July followed by dry warm weather may start the mildews and black-rot. A normal rainfall is needed in August and Sep- temper to develop the fruit and there should be plenty of sun- shine. Warm weather with sunshine is necessary in the fall to allow for late picking. 299. Sugar-content. — In northern Ohio the sugar-content of white and Catawba grapes increases the longer they are left on the vines in the fall, consequently the growers delay picking as long as possible. Warnings of cold weather or sleet storms are desirable at this time to hasten pick- ing. In the hot valleys of southwestern Europe, grapes have a very high sugar-content and although they ripen early they sometimes become very sweet before they are ripe. WEATHER AND CROPS 133 Olives 300. Temperature. — The olive is very drought-resistant. Its range is restricted by temperature, although there is con- siderable difference in the varieties in the resistance to cold. In California, the winter mean temperature where olives are grown should not be below 48° and the summer mean should seldom exceed 80°. The dormant trees should not be sub- jected to a temperature below 15° to 20° and seldom below 28° or 30°. The fruit is very sensitive to frost and is seri- ously injured by a temperature of 28° even for a short time. The trees require a mean annual temperature of about 57°, and a mean temperature of over 66° for several months, at least during the first of the season, seems necessary. They blossom in an average year when the mean daily temperature reaches 66°. Olives are peculiarly well adapted to southern Arizona where they are not injured by the heat of summer and very rarely is the fruit damaged by the cold of winter. Peaches Peaches are raised most extensively in the United States from northeastern Texas and Arkansas eastward to the At- lantic Coast and northeastward to the lower Lake region, and in California. About three-fourths of the peach trees are south of the Ohio and Missouri rivers and in California. The mean winter isotherm of 25° is a fairly well-defined northern limit for extensive peach production. 301. Temperature effects. — When thoroughly dormant, peach-buds will withstand a temperature of 12° to 20° below zero (F.), depending somewhat on the variety. Thorough dor- mancy is, however, somewhat indefinite and not very con- stant. Peach-buds are advanced easily by short spells of warm weather in even late fall or early winter and will then be killed by temperatures only slightly below zero. 302. Critical temperatures in Missouri (Chandler). — The killing temperature of peach blossoms when the tree is just coming into full bloom, under Missouri conditions, seems to vary from about 22° to 26°. After the blossoms are old enough so that they are probably pollinated, and from that time until the peaches are as large as half an inch in diame- 134 AGRICULTURAL METEOROLOGY ter, they continue to grow more tender until they will with- stand but a few degrees below 32°, the seeds of the young peaches killing at a higher temperature than other peach tis- sue. The length of time subjected to the low temperature is an important factor. 303. Temperature and peach trees. — Thoroughly dor- mant peach trees will usually stand a temperature of 5° to 10° lower than the buds. The injury to trees depends, however, on the condition of the trees, the duration of the cold, the soil and surface cover, and the rapidity of thawing. 304. Moisture and peaches. — Like other stone-fruits, peaches require plenty of moisture for proper development. The Utah Agricultural Experiment Station Bulletin No. 142 states that ''No amount of water applied early in the season to a crop of peaches on gravelly soil will compensate for the lack of water during the month before harvest." 305. Weather and the yield of peaches. — Quite extensive studies of the relation between the mean temperature and total rainfall for different months and the yield of peaches in northern Ohio have given no well-defined correlation. 306. Diseases of peaches. — Leaf-curl in Ohio is developed by cool, rainy, and cloudy weather. It is said that profitable spraying may be predicted with fair certainty from a knowl- edge of the temperature and rainfall in the first half of April. Warm moist weather conditions during May and June appear to be especially favorable to the development of the peach- scab fungus in New Jersey. Pears 307. Pears are raised most extensively in the north- eastern part of the country, in the Pacific states, and in a small area in western Colorado, although many are grown in other districts except in the upper Mississippi and Missouri valleys and in the central ,and upper Great Plains. Plums 308. Plum trees of different varieties are widely scattered over the eastern half of the country, but the most intensive development of this crop, particularly the variety that is dried for prunes, is in central California. Plums thrive best in an WEATHER AND CROPS 135 equable climate with a long growing season, plenty of sun- shine, freedom from frosts and from early fall rains and fog. They cannot endure extremes of heat and cold and of wet and dry weather. Prunes are a variety of plum that can be dried without the removal of the pit, without fermenting. ''All prunes are plums, but all plums are not prunes." Strawberries Strawberry cultivation is widely distributed, but the largest intensive areas are in southern New Jersey and eastern Mary- land and in northwestern Arkansas. 309. Moisture and strawberries.— The plants need an ample supply of moisture in the soil constantly during the growing season and particularly while bearing fruit. 310. Temperature effects.— The blossoms are injured by a temperature below 30°. The young fruit endures a tem- perature below 24° at the ground and green fruit lower than this. The ripening fruit endures less cold. Moderate tem- perature and comparatively dry weather is desirable during the harvest season. High maximum temperatures during blossoming are detrimental as it prevents the setting of fruit. 311. Harvesting.— The average date of harvesting the crop is as follows: South-central Florida Dec. 1 to April 1. North Florida Feb. 10 to May 15. South Texas March 1 to May 15. South Louisiana March 15 to May 20. North Gulf and South Atl. Coast April 15 to June 1. Lower Ohio Valley and Northern Maryland May 15 to June 20. Southern New England and lower Lake region June 1 to July 15. 312. Adaptation to climate (Farmers' Bulletin No. 1043). — ''In the selection of a variety for a given locality one should first determine whether it is suited to its climate. Thus, the Missionary, which is a good shipping variety in central Flor- ida, is not a good shipping variety in the upper Mississippi Valley. In the southern States the Missionary and Klondike make a quick growth in early spring, producing large crops 136 AGRICULTURAL METEOROLOGY of early berries and in those parts of the South suited to them they are excellent shipping sorts. Neither of them, however, is adapted to the climatic conditions found in the northern states. In like manner, the Dunlap, a leading northern sort, is not adapted to southern conditions; when grown there it is too soft for shipping and sometimes too soft even for local markets. ''Other varieties, such as the Glen Mary, Belt (William Belt), and Marshall, which are grown to a considerable ex- tent in the northeastern States, are not adapted to conditions farther south because of their greater susceptibility to leaf- spot diseases. The Clark, Jucunda, and other varieties grown in the dry atmosphere of the irrigated sections of the West are not grown in the East, and whether they would do well under the humid conditions in eastern sections is perhaps doubtful. It is important, therefore, to know the climatic adaptations of the different varieties before selecting them for extensive planting." 313. Strawberry diseases. — Leak, caused by Rhizopus nigricans is by far the most important rot of strawberries after picking. It develops very slowly at 50° but increases rapidly with higher temperature. Berries picked early in the morning are cooler and will ship better than those picked near the middle of the day. Botrytis sp. is a field rot of strawber- ries that is most abundant and serious under conditions of excessive moisture. Citrus fruits Citrus fruits are of tropical origin and the intensive culti- vation of oranges, lemons, grapefruit, and limes is generally confined to places without severe frosts. They are success- fully grown, however, in regions in California where frosts oc- cur, although artificial protection from low temperature dam- age is usually resorted to. 314. Oranges. — The most extensive orange orchards in the United States are in central Florida and southern Califor- nia, although they are raised in central California and in the Gulf coast districts of Texas, Louisiana, Mississippi, and Ala- bama. It has been found in California that the ripe orange begins to freeze when the temperature of the fruit itself reaches 28° F. The rind freezes first and the rapidity with WEATHER AND CROPS 137 which the freezing extends inward depends on the air tem- perature and radiation. The temperature of the fruit lags from one to two and one-half hours behind the air tem- perature, depending on the rate at which the air tempera- ture falls. When the temperature is falling rapidly, that of the fruit is sometimes 7° higher than that of the outside air. 315. June drop of navel oranges. — Navel oranges grown in the interior valleys of California and Arizona are subject to a large shedding of young fruit usually called "June drop" although it may occur at any time from the petal-fall in April to maturity. The period from petal-fall until the fruit is about 1 inch in diameter is the most serious. While this drop increases with high average daily temperature, many practical orchardists in California believe that the amount of the June drop depends primarily on low temperature during the preceding winter and secondly on the high temperature in summer. 316. Oranges in Florida. — The annual growth of oranges in Florida is divided into four well-defined periods: (1) when spring blossoms are appearing and the young fruit forms. This is the most critical time from a moisture standpoint as dry weather may cause the young fruit to drop. (2) During the summer when fruit takes on size. Rain is needed, as a dry period may do serious harm by preventing fruit from attain- ing full size and color. (3) Fall and early winter when fruit is maturing and harvest begins. A severe cold wave at this time may cause great damage by freezing. (4) Dormant sea- son which is usually through December and January. 317. Lemons. — The principal lemon district is in south- ern California. The lemon is more tender than the orange and the fruit is injured at 26° to 28°, and sometimes at even higher temperatures. Young small sized fruits, ''button lemons" are more tender than those large enough to harvest. The damage to lejnon trees by winter cold depends in a large degree on the age of the trees. Trees five years old have been frozen to the ground with a temperature of 19°, while old trees were not seriously injured. 318. Limes are raised in Florida and California. They are more tender than lemons and the fruit is killed at temper- atures of 28° to 30°. 138 AGRICULTURAL METEOROLOGY 319. Pomelos (grapefruit). — The grapefruit trees are more hardy than the lemon but are more tender than orange trees. The fruit is not so easily frozen as are oranges. Te7nperatures withstood 320. Critical frost temperatures for fruit. — ^The tempera- ture at which fruit-buds will be killed depends on so many factors that no well-defined limit can be designated. The con- dition of the tree, the stage of advance of the buds or blos- soms, their position on the tree or limb, the moisture in the atmosphere, the length of duration of the low temperature, and the previous weather that the tree has been subjected to, all enter into the problem of frost damage. 321. Percentage of damage. — It has been pointed out that there is a range of at least 5° between the temperature at which all of the buds will be killed and that at which only 5 per cent will be lost. If there are few blossoms on a tree, the critical temperature, therefore, will be higher than when it blossoms so freely that a large percentage can well be lost and yet leave as many as should develop fruit. As a usual thing, if only 2 per cent of the live buds of peaches remain to mature, it will mean a fair crop of fruit. It is frequently said that a fruit-tree in an average year should lose about 90 per cent of its buds or blossoms. 322. Critical temperatures relative. — The critical frost temperature then is a relative term depending on the per- centage of blossoms that need to be saved from loss. 323. Safe temperatures. — The following table gives what are believed to l^e safe temperatures for the normal tree in an average season under usual conditions. Under some condi- tions it is known that the temperature may fall several de- grees below these values without serious loss. In general, how- ever, when protection by heating is practiced, it is wise to prevent the temperature going below the point indicated for any great length of time. The figures are from observations by a number of experts or from actual tests by men of author- ity. Careful records of minimum temperatures and amount of damage on cold nights should be kept for future reference by every orchardist, especially if heating is done. WEATHER AND CROPS 139 Table 11. — Probably Safe Temperature for Different Fruits Buds show- In full Kind of fruit ing color bloom Fruit setting Apples 27 29 30 Apricots 30 31 32 Almonds 28 30 31 Blackberries 28 28 28 Cherries 25 28 30 Grapes 31 32 32 Lemons — 32 30 Pears 28 29 30 Peaches 25 28 30 Plums 30 31 31 Primes 30 31 31 Oranges 30 30 — Raspberries 28 28 28 Strawberries 28 28 28 324. The orange tree when fairly dormant will stand a temperature of 25° to 26° for an hour or so. At 20° to 22° the twigs begin to die back and the leaves fall. At 17° to 18° for four to five hours, the branches will be killed back to 2 or 3 inches in diameter, unless the trees are quite dormant. 325. Peaches. — West and Edlefsen in freezing experi- ments in Utah in which by an ingenious device they were able o freeze the buds on a detached limb or on the whole tree, -jund that the temperatures which will kill about 50 per cent buds of the Elberta peach are as follows: When slightly swollen, 14° : " well " 18° " showing pink, 24° " full bloom, 25° " setting fruit, 2S° J26. Cranberries. — Careful records in Massachusetts show that in the greenish white stage that immediately per- cedes the ripening of fruit, the berries will endure a tempera- ture of 26° without harm, and 25° with little injury, but 24° seems to harm such fruit greatly if it continues long. 327. Dormant period. — In the northern part of the United States, fruit-trees should stop growing early so as to become fully dormant before th^ low temperatures of late 140 AGRICULTURAL METEOROLOGY fall and winter occur. In the southern states, however, where little or no damage occurs during the dormant period, the problem is to keep the fruit-trees growing as late as possible so that the short dormant period will carry the trees through the spells of warm winter weather. Otherwise the buds de- velop too far and are killed by later cold. 328. Most susceptible period. — It is believed that the peach is the least resistant to cold when it is about the size of a pea, when the calices are falling. The seed kills at a higher temperature than other plant tissue. After setting, the dam- age to young apples is due to the freezing of the stems. 329. Weather and the setting of fruit. — Warm dry sunny weather is most favorable for the setting of fruit while cold and rainy weather is detrimental. Rain prevents bees and insects from- carrying the pollen while the secretion on the stigmas or the pollen on the anthers may be washed away, or the pollen-grains may swell and burst. 330. Temperature effects. — In very warm weather the stamens, or male part of the blossom, will develop more rap- idly than the pistil, or female organ. Thus under high tem- peratures the stamens may be forced so much faster than the pistil that the pollen is shed before the pistil is ready to re- ceive it. In cool weather the pistil develops most rapidly. The pistil is often injured by a light frost that does not affect the stamens. It has been determined that the pollen of the apple will withstand much lower temperatures than will any other tissue of the flower when in full bloom. 331. The killing of plant tissue. — During freezing weather ice forms in the inter-cellular spaces of the plant tissues and withdraws the water from the protoplasm in the plant-cells. It was formerly taught that if plants thawed slowly enough so that the cells could reabsorb the moisture as fast as the ice melted, little harm would result. Chandler and others have demonstrated from experiments, however, that the rate of thawing does not have anything to do with the amount of killing, at a given temperature. 332. Frost is most damaging when fruit is wet. — A plant tissue with a wet surface kills worse at a given temperature than tissue with no moisture on the surface. 333. Sun-scald on the southwestern or sun-exposed side of the trees is brought about by some interaction of sun and WEATHER AND CROPS 141 cold in late winter, and is common in northern districts. The injury occurs late in winter or early in spring when warm days are followed by cool nights. The bark is subjected to rapid and extreme temperature changes, becomes unhealthy, dies, dries up, and falls away. It is prevented by spraying or painting trunks with whitewash. LABORATORY EXERCISES The possibilities of personal investigation on the part of the student are self-evident in Chapters VII, VIJI and IX. Each student should be given some specific crop, plant disease, or in- sect, and directed to show the relation between the weather and its de- velopment from past records. At the proper season valuable information can be obtained by noting the effect of current weather on crops, particularly fruit or truck. REFERENCES Fiber Crops Correlation of Weather Conditions and Production of Cotton in Texas. J. B. Kincer, Monthly Weather Review, February, 1915. Forecasting the Yield and the Price of Cotton. Henry L. Moore, The Macmillan Co., 1917. Hemp. L. H. Dewey. Yearbook, 1913. Some Recent Studies of the Mexican Cotton Boll Weevil. W. D. Hun- ter, Yearbook, U. S. Department of Agriculture, 1906, pp. 313-324. Fruit Almond in California, The. R. H. Taylor, California Experiment Sta- tion Bulletin No. 297. California Division of Agricultural Education Extension Courses, 1918. Currents and Gooseberries, Farmers' Bulletin No. 1021. Drought Resistance of Olives in the Southwestern States. S. C. Mason, Bureau of Plant Industry, Bulletin 192. Experiment Station Work with Peaches, Annual Report of Experiment Stations, 1906. Frost and Temperature Conditions in the Cranberry Marshes of Wis- consin. H. J. Cox, Bulletin T, U. S. Weather Bureau, 1910. Frost and the Prevention of Damage by It. Floyd D. Young, Farmers' Bulletin, 1096. 1920. Strawberries, Varieties in the United States, Farmers' Bulletin 1043. U. S. Department of Agriculture Bulletin 462. CHAPTER VIII THE EFFECT OF WEATHER ON THE YIELD OF GRAINS The bread and feed grains are the fundamental crops, aside from the earth-cover of grass. The yields of them are major factors in determining the financial movements of the year, and the quotations on them figure largely in stock exchanges and price-currents. The relations of weather and climates to these crops is a question of large public concern. BARLEY Spiking barley has. a» shorter growing., season than either wheat or oats and is cultivated farther nortii and at higher altitudes than other cereals. It is grown up to latitude 70 degrees in Norway and to 653^2 degrees in Alaska. It ripens in 80 to 95 days after seeding in Alaska, and in about the same time in Wisconsin. 334. Range in the United States. — The main spring bar- ley districts are in Wisconsin, Minnesota, North Dakota, South Dakota, and California. Some winter barley is grown in the South. 335. Temperature and barley. — While some varieties of barley are grown on the tropical plains of the Ganges and in the hot districts of northern Africa, most of the crop in the United States is grown in a cool region. It serves as a crop where it is too cool for corn. All of the principal barley dis- tricts in this country do not have any month during the season of growth with the mean temperature above 75°. It has been found in England that the chief requirement as far as yield is concerned, is a cool summer, especially after mid-June. It is affected by spring frosts more than either wheat or oats but recovers quickly. Winter barley is not so hard}^ as win- ter wheat or rye. 142 WEATHER AND YIELD OF GRAINS 143 336. Rainfall and barley. — The principal barley-growing districts of the United States receive an annual rainfall of less than 35 inches. In parts of California it matures on an an- nual rainfall of less than 10 inches, although spring barley should have about 10 inches of rain during the three months of growth. For brewing purposes, barley must be raised where there is little rainfall during the latter part of its growth and none while in shock. The crop needs plenty of sunshine and should ripen in dry weather without dews. 337. Critical period of growth. — April, June, and July are the critical months for barley. Barley is not an important crop in Ohio, but a study covering thirty-eight years shows that the best yields are nearly always with a comparatively dry June, while wet Junes are almost never accompanied by yields much above the normal. 338. In Wisconsin. — A correlation of the weather with the yield of barley in Wisconsin, during the period from 1891 to 1917, shows the following: Rainfall Temperature Correlation Probable Correlation Probable Month coefficient error coeffi,cient error April —0.36 ±0.11- +0.32 ±0.12 May -1-0.32 ±0.12 —0.05 June +0.20 ±0.12 —0.55 ±0.09 BUCKWHEAT Buckwheat will mature in a shorter period than any other grain crop, ten to twelve weeks being sufficient under favor- able conditions. It is, therefore, well adapted to high alti- tudes and shof t seasons, but its period of growth must be free from frosts as it is very sensitive to cold. Because of its short growing season, it is successfully cultivated as far north as 70 degrees. Its cultivation in the United States is confined largely to the northern states east of the Mississippi River. The district of chief production is in the Appalachian region from West Virginia to New York, with a secondary district in Michigan. 339. Weather and buckwheat. — A cool moist summer climate best suits this crop, very little being grown in the United States where the summer mean temperature is over 70° and practically none where it exceeds 75°. 144 AGRICULTURAL METEOROLOGY The seeds will germinate best when the soil temperature is about 80°F., although they will germinate when the tem- perature is anywhere between 45 and 105. In order to ger- minate, the seeds must absorb about one-half their weight of water. Considerable heat in the early stages of growth is an advantage, but it should be cool and moist during the latter part of growth and especially when seeds are forming, The plants are very sensitive to high temperature and dry weather at blooming time, especially when both day and night are hot or when accompanied by hot, drying winds. Hot weather with constant rain is also unfavorable. In experiments in Russia covering a period of fifteen years, the good years were with a comparatively low temperature during the second half of the flowering period and the poor yields where the temper- ature was relatively high. -It was found there that a drought during blossoming caused a large production of straw, but of very little grain. By sowing buckwheat before April 25, through a long series of years in Russia a type had been pro- duced that resists a temperature several degrees below freez- ing. CORN Corn or maize is a sun-loving crop of tropical origin, but is so flexible in its requirements and so readily adapts itself to its surroundings that it is successfully grown over wide climatic ranges. It does not mature, however, anywhere north of the 50th parallel of latitude, although it may be grown for green fodder in favored localities somewhat far- ther north. ^ 340. Where grown. — The great corn regions of the world are areas of continental climate. Except where irrigation is practiced, most corn is grown in regions having an annual rainfall of over 20 inches and a summer temperature averag- ing about 75°. A comparatively small area of the earth's sur- face is devoted to the intensive cultivation of this crop as the optimum climatic conditions for corn are found in only a few regions of the world. Outside of the United States, the im- portant corn-producing regions are in Roumania, Hungary, Mexico, Argentina, and India. Corn does not thrive in re- gions of cool cloudy summers. WEATHER AND YIELD OF GRAINS 145 341. In the United States. — Corn is preeminently an American crop and is grown on three-fourths of all the farms of the United States. Every fourth acre, almost, of improved land in this country is a corn field. In America ''corn is king." This country contributes about 70 per cent of the world's total production. The corn acreage as well as its value is greater than that of wheat, oats, barley, rye, buckwheat, rice, fruits, and nuts combined. The 1910 census shows that for each dollar the farmers of the nation received for grains Fig. 37. — Where corn is grown in the United States. over 50 cents came from corn. Fig. 37 shows two centers of greatest production in this country, and makes plain the fact that a large percentage (three-fourths) is raised in the Missis- sippi Valley. While a large proportion of the total corn crop is raised in this comparatively limited area, it is an important crop in nearly all the eastern states. 342. Climatic factors. — The region of most intensive cul- ture in this country is within a territory where the mean sum- mer temperature is from 70° to 80°; the average daily mini- mum temperature in summer is over 58°; the average frostless season is over 140 daj^s; has an annual precipitation between 25 and 50 inches, and a rainfall of 7 to 8 inches in July and August. 146 AGRICULTURAL METEOROLOGY 343. Climatic limits.— The growth of corn in any quan- tity is Hniited on the north by the mean summer isotherm of 66° and by the average summer night temperature of 55°. The western hmit of extensive cultivation agrees closel}^ with the summer (June, July, and August) rainfall line of 8 inches, especially in the Southwest where summer droughts are likely to prevail, and where evaporation is hastened by hot Fig. 38. Dates when corn planting begins. winds. As a result, very little corn is grown along the north- ern border of the country or in the West except in the more favorable locations. 344. When planted.— As shown by Fig. 38, the planting of corn usually begins in extreme southern Texas the latter part of January and this work progresses northward at an average rate of thirteen miles a day, reaching the northern limits of the country about the middle of May. Planting be- comes general in the principal corn states about May 15, and is usually completed by June 1. WEATh^ER AND YIELD OF GRAINS 147 345. Temperature and planting dates. — It is an interest- ing phenological fact that the average date of the beginning of corn planting agrees closely with the date when the sea- sonal rise in the mean daily temperature reaches 55°. If the date lines on Fig. 39 are drawn on the beginning of planting Fig. 39. — Mean daily temperature when corn planting begins in different parts of the United States east of the Rocky Mountains, and the dates on which these temperatures are reached. chart, the lines of the same dates would almost exactly coin- cide all the way from the Gulf to the Lakes. 346. Com planting and average frost dates. — As the aver- age last spring frost date lines also agree closely with the tem- perature of 55°, it follows that the average date on which the last killing frost in the spring occurs has been found to be the best date for begirming of corn planting. The ground becomes warm enough l^y that time for the germination of seed and the danger of serious frost damage will be over by the time the corn comes up. 148 AGRICULTURAL METEOROLOGY 347. When harvested. — The beginning of the corn har- vest does not progress so regularly as the beginning of plant- ing, partly because of various methods of harvesting the crop in different sections. Fig. 40 shows the average date when cutting and shocking begins. 348. Length of the growing season of com. — Taking the dates for the beginning of planting and those of cutting and Fig. 40. — Dates when the cutting and shocking of corn begins, in an average season. shocking as a basis, the average length of the growing and ma- turing season of corn is obtained. This varies from 150 to 180 days in the South to 120 to 130 days in the North. In the main corn-growing states it varies from 130 to 150 daj^s. 349. Varieties and length of growing season. — Although a tropical plant, corn will adapt itself to the climatic require- ments so that different varieties have developed that will mature in the possible growing season even beyond the 47th WEATHER AND YIELD OF GRAINS 149 degree of latitude. That this is not a recent development is shown by the fact that corn was being successfully grown by the Mandan tribe of Indians in the Missouri Valley in North Dakota when first visited by the whites as early as 1738, and had apparently been so cultivated extensively for several cen- turies at least. They were growing varieties that matured in 70 to 90 days. 350. Temperature and corn. — Corn will germinate in three to four days at a temperature of 62°. The length of time necessary for germination increases as the temperature lowers until the minimum temperature for possible germina- tion is reached. In some experiments in New York, one va- riety of corn required 430 hours and another 460 hours to germinate at temperatures between 37° and 42°. In a test by Haberlandt,^ eleven days was required at a soil tempera- ture of 51° for the sprouts to show, while only three days were necessary when the soil temperature was 65°. In De Can- dolle's experiments corn germinated in ten to twelve days at temperatures of about 49°, but in less than two days at tem- peratures from 70° to 84°. The optimum temperature for germination is given as 91° to 93°, and the maximum beyond which germination will not take place as slightly above 115^. 351. Growth and temperature. — Lehenbauer determined from experiments that corn seedlings in practical darkness and a constant relative humidity of 95 per cent, made almost no perceptible growth when the temperature was 40° F. (4.5° C), the most rapid growth was at 89.6° F. (32° C.) and that the growth ceased at 118.4° F. (48° C). (See Fig. 19). His experiments showed that the rate of growth doubled with each increase in temperature of about 18° F. from the mini- mum to the optimum temperature and decreased in about the same proportion from the optimum to the maximum temper- ature. The rate of growth w^as practically the same at 116° as at 40° while at 88° it was 122 times as great. The rate of growth at the different temperatures varied with the length of time exposed, which at the figure cited was twelve hours. The experiment is valuable only as an indication, as corn plants in the field are never subjected to the conditions im- posed on the seedlings in the experiment. 1 111. Agr. Exp. Sta. Bull. 208. 150 AGRICULTURAL METEOROLOGY 352. Moisture and corn. — The corn plant is made mostly from water and air, with food taken in solution from the soil by the roots, and carbon taken from the air by the blades. The plant makes the grain by the aid of the sun. The heat, moisture, and sunshine must be properly balanced to produce the best results. 353. Transpiration and leaf area. — The amount of water transpired from a given leaf area of corn (based on expanse of leaf rather than both surfaces) has been found to be about one-third as great as the evaporation from a free water sur- face of the same area. In hot dry weather, the rolling of the leaves reduces the transpiration rate. 354. The moisture requirements of com vary at different periods of growth and with plants of various sizes. Young and small plants do not require as much moisture as larger and older ones. The amount of water used each week of growth gradually increases until the maximum leaf area has been developed. This brings the maximum water require- ment of corn when it is tasseling and earing. The require- ment continues high for four or five weeks, then falls off rather rapidly until ripening takes place. 355. Best dates for planting corn. — Wherever the length of the growing season will allow for varying the date of plant- ing, it is important to have the corn reach the tasseling and ear-forming period when a large amount of rain usually falls and when the temperature is relatively high. If the crop is irrigated, it should be given the maximum amount of water at this time. When the plant is tasseling, it has received prac- tically all of its growth. It builds frame-work and constructs cells which will be filled with food matter later. 356. Measurements of water requirements vary, as in- vestigators have used different methods of determination and under varied environments. Briggs and Shantz determined that corn requires an average of 368 pounds of water for every pound of dry matter produced. (See par. 201.) Taking into consideration the water lost by evaporation, it is calculated that the water requirement for each pound of dry matter, under average field conditions, will be at least 500 pounds. 357. The amount of dry matter in the stalks and leaves is about the same as in the grain. Hence 112 times 500 or 56,000 pounds (28 tons) of water will be required to produce WEATHER AND YIELD OF GRAINS 151 each bushel of corn. A 50-bushel crop of corn then requires 1,400 tons of water. As one inch of water over an acre of ground weighs 113 tons, it will require theoretically 12.39 inches of rainfall to produce a crop of 50 bushels to the acre, on an average. The run-off is probably one-third of the rain- fall in an average season, so that something like 18 inches of rain would be required for a 50-bushel crop. 358. Seasonal rainfall.— A study of rainfall charts shows that the actual rainfall from planting to harvesting of corn is greater than this in the southern states, but considerably less in the North. . ^ „ . , 359. Rainfall and the yield of corn.— Rainfall is the most important weather factor in varying the yield of corn in the corn-belt district of the United States. The critical period when rain is most essential is from the middle of July to the middle of August; the most important calendar month, how- ever, is July. . 360. July rainfall and com yield.— Fig. 41 shows the relation between the rainfall for the month of July and the yield of corn over the states of Ohio, Indiana, Illinois, Iowa, Nebraska, Kansas, Missouri, and Kentucky for the twenty- eight years from 1888 to 1915, inclusive. The averageram- fall over these states for July for twenty-eight years is 3.9 inches. The average yield of corn is 29.7 bushels to the acre. The lines show the variation of the rainfall and yield for each year from the mean for the whole period averaged for the eight states as a whole. For example, in 1889 the aver- age rainfall was 1.0 inch above the normal and the yield of corn was three bushels to the acre above the normal or close to 32 bushels. In 1902 the rainfall was close to 5.0 inches and the yield averaged nearly 33 bushels or about 4 bushels to the acre above the normal. 361. The two curves agree.- The two curves run closely together most of the time, although there are some well- marked exceptions. This shows that while the rainfall m July is an important variant, it is not the controlling factor .^ The temperature must be considered, as well as the rainfall m Au- gust, and, to some extent in June. An inspection of the dia- gram shows that whenever the rainfall for July has been above the normal, the yield was above the normal m every instance, although in 1896 and 1915 the rainfall was evi- 152 AGRICULTURAL METEOROLOGY S/61 i^/6f e/6t e/61 116/ 0161 606t 8061 1061 906/ 906/ toe/ €06/ 206/ /OS/ 006/ 669/ 968/ 168/ 9691 £69/ f68/ €68/ 268/ /68/ 068/ 688/ 889/ K : . "^--^ _. ^ "^^s.^^ .^^ ^^ ^^-^ ^^ r ^ \ '■^^ \^ N. ^^ / ' X 1 1 ^^ ^^ ^ ^ -^ -^ -^:^ nn:^ — — r^:^ F=^ -— "^ A \ r ^-> J ^_ .-• "^^^ ■^^^^ =-^ =^-=i* <^ r*^ 5'*^ ^ r^-^ .-^'^ V ""' ^=^^ "r^ — s=^ .1 r^' r=^ rssrs. >■ V ^1 nVJA//V8 ^ < ? " 1 ■ a 7 J/ A >0 V V -K S 1 1 1 1 1 , T3 I -73 c3 'H 1-1 WEATHER AND YIELD OF GRAINS 153 dently too great for the best yield. Whenever the rainfall was below the normal, the yield has been also below in every year except five and in two of these exceptions the rainfall was practically normal or only slightly below, and in one other the yield was just about normal. 362. July rainfall and com yield averages. — If the years of different rainfall amounts are grouped together, it will be found that whenever the rainfall has been one-half inch or more above the normal, the yield of corn has averaged 10 bushels to the acre more than when the rainfall has been one- half inch or more below the normal. Taking into considera- tion the average acreage devoted to corn in these states and the average yield in bushels to the acre for the past ten years, it will be found that this average of 10 bushels to the acre means a definite increase in the corn crop over the eight states of something like 500,000,000 bushels, with this variation in rainfall. When corn is worth $1.00 a bushel, this increase in the corn yield wijl increase the purchasing power of the farms in the central part of the United States fully $500,000,000 through corn alone. 363. The four greatest corn states. — It is stated that, of the total acreage of corn in the United States, 30 per cent is grown in the four states of Indiana, Illinois, Iowa, and Mis- souri. Of the total amount shipped out of the county in which it is grown, 60 per cent is raised in these four states. The average yield of corn is 32 bushels to the acre, and the average rainfall for July is 3.9 inches. Fig 42 shows the rela- tion between the rainfall over the four states for the month of July, as compared with the yield of corn in bushels to the acre, over the same area. The years are shown at the top of the diagram and run from iteS to 1915, inclusive. The lines show the variation of the rainfall and yield for each year, averaged for the four states as a whole, from the mean for the entire period. While the two curves are fairly uniform, there are some variations which show plainly that other weather factors besides the rainfall for the month of July must be taken into account in consider- ing the effect of the weather on the yield of corn in these states. 364. Comparisons close. — However, when the rainfall has been above the normal, the yield has been above the normal in every year but two. This shows a probability of the yield 154 AGRICULTURAL METEOROLOGY 9/6/ trie I C/6/ a/61 //6/ 0/6/ 606/ 806/ 106/ 906/ 506/ P06/ €06/ eo6/ 106/ 0061 6681 8681 1681 9681 S6QI peai tSdl Z68I /egi 0681 688/ 988/ " ■ ' ::*^ — > / , •^ ^ , — - - — - r^ ~"~-- --- -^^ ^---^ ^ ^--' ':^^X-^ \ L "^^^ ::>^ , -^ y' r^ ^^ — . — . / r— " --- -^ N s^- \ \ ^=^ r*^ U.5=^ ^-=:i^ ^^=^ =.=^ :::::^ .. 4»ad ___, --^ ZT^ :rrr "" •< -">.-. \ i ^^ \ "^ ^^j \ =^^-^ =^ "^ ^■=rr U^ S-^^^ ^ ^^ \ ^ >-. ::;^ "~-~. --> \. ^\ r^=^ ,-^ / hi s.. nvjMVhl a 13 /A O 7 WEATHER AND YIELD OF GRAINS 155 of corn being above normal 85 per cent of the time when the rainfall in July is greater than the average. An inspection of the curves shows also that in only four of the years when the rainfall was below the normal was the yield greater than the average. This makes a probability of 73 per cent that the yield of corn will be below normal if the rainfall for the month of July is below the average. 365. Striking averages. — A complete analysis of the rain- fall and yield data in these states shows that the average in- crease in the yield of corn with each increase of one-half inch in the rainfall in July amounts to 2 bushels to the acre, or a total increase in the corn yield of 60,000,000 bushels. When the rainfall for July in these four states has been between 2 and 2.5 inches, the yield of corn has averaged 23 bushels to the acre, and when the rainfall has been between 2.5 and 3 inches the yield has averaged 33 bushels to the acre. This is an increase of 10 bushels to the acre with an increase of only one-half inch of rain at the critical rainfall stage. This in- crease amounts to the enormous quantity of 300,000,000 bushels, worth something like $300,000,000. This also means an increase in the value of the corn crop of SIO an acre when corn is worth SI. 00 a bushel. 366. Rainfall and temperature, and corn yield. — Fig. 43 shows by means of a dot chart the combined effect of the July rainfall and temperature on the yield of corn in Ohio during the period from 1854 to 1915, inclusive. In the chart, the hea^^ horizontal line represents the normal temperature for Ohio for the month of July, which is 74°. The figures at the left mark lines which represent the variation of the temperature above or below the normal as indicated b}^ the prefixes plus or minus. The heavy perpendicular line indicates the normal rainfall for the state for July, and is close to 4 inches. At the top the figures indicate the variation of the rainfall above or below the normal. The plus and minus signs in the diagram indicate yields of corn above or below the normal, respec- tively. . The dot chart is made by placing a yield mark for any year at a spot on the chart where lines showing temperature and rainfall departures from the normal for that year will inter- sect if drawn across the chart; for example, in 1866 the tem- perature for July averaged 2° a day above the normal while 156 AGRICULTURAL METEOROLOGY the rainfall was one inch greater than the normal. The corn jdeld dot will therefore be placed at the intersection of the lines representing these values and as the yield for that year was greater than the average, the plus mark was placed at this point. The amount of the variation of the yield from the normal is not indicated. If, in making a diagram of this kind, the plus and minus signs are scattered promiscuously over the chart, it will show that there is no relation between the weather conditions and *7 *-6 f-4 ♦ 2 + 1 |u: a -I -2 -3 -A 3 -2 -1 INCHES +1 +2 +3 +4JI * J. • < - Q WARM a DRY i. , WARM a WET II + + ♦ • + + - N ORM ++ . s ^ +. ^PEfi ATUF - - 1*- - + - + ^ + + J -• + + + . ^ + C ;ooL a DRY + z .5 < ;oot- & WE • +q: =J •* YIELD ABOVE NORMAL • YIELD BELOW NORMAL Fig. 43. — Effect of July rainfall and temperature on the yield of corn, Ohio, 1854-1915. the yield. If, however, there is a grouping of like signs on one side or in one quarter of the diagram, then a relation is shown. 367. Wet weather important. — In this diagram, it will be seen clearly that there is a decided grouping of the plus marks to the right or on the "wet" side of the normal rain- fall line, and of the signs to indicate the yield below the nor- mal on the left or "dry" side of the rainfall normal. If only those years are considered when the rainfall departed one inch or more from the normal, it will be seen that when it was wet the corn jdeld was above the normal thirteen times, and below only once. This indicates that when the rainfall in WEATHER AND YIELD OF GRAINS 157 Ohio for July is one inch or more greater than the normal, the probability of a good corn crop is 93 per cent. On the other hand, when the rainfall was one inch less than the normal the yield was above the normal three times and below thirteen times. This indicates a probability of a good corn yield of only 19 per cent when the rainfall in July is 3 inches or less. 368. Rainfall and corn yield averages. — If all the years when the rainfall for July in Ohio has been less than 3 inches be grouped together, it will be found that the yield of corn averaged 30.3 bushels to the acre, and when the rainfall has been 5 inches or more the yield has averaged 38.1 bushels to the acre. This difference of 7.8 bushels an acre means a va- riation of 27,300,000 bushels of corn for the state, worth nearly $8 an acre or over $27,000,000, depending on whether the state has had an average rainfall of 3 inches or less in July or whether the fall has been 5 inches or more. 369. Temperature effect not so important. — The effect of a difference in the mean temperature in July in Ohio in vary- ing the yield of corn is not so well marked, as is shown by the fact that there is an irregular grouping of the plus and minus signs above and below the normal temperature line in Fig. 43. 370. Combined rainfall and temperature effect. — The combined effect of these two weather factors is shown by the grouping of like signs in the different quadrants of Fig. 43. For example, in the upper right-hand quadrant, which would indicate a wet and warm July, there are eleven plus signs and only two minus signs. This indicates that when July in Ohio is warm and wet, the probability of the corn yield being greater than average is 85 per cent. When it is cool and wet, the probability of a good corn yield is 73 per cent. On the other hand, when July is cool and dry, the probability of a good corn yield is only 38 per cent, and when July is warm and dry it is only 33 per cent. 371. Average July rainfall and corn yields in Ohio. — In this state, with each increase of one-fourth inch in the rain- fall in the month of July, the average increase in the yield of corn will be close to 1 bushel an acre ; and between 2 and 4 inches the average increase in the yield with each increase of one-fourth inch in the rainfall will amount to 1 3/2 bushels to the acre, the value of which will be almost $6,000,000. A further combination of the figures will give the results that 158 AGRICULTURAL METEOROLOGY each increase in the rainfall in July of one-half inch will cause an average increase in the corn yield in Ohio of 4,200,000 bushels, and when the rainfall in,July passes the 3-inch mark the increase in the corn crop with an increase in the rainfall of only one-half inch will, on the average, amount to 15,050,000 bushels, valued at over $15,000,000 when corn is worth $1.00 a bushel. 372. Correlation for shorter periods than months. — The rainfall in the preceding correlations and discussions was for complete months, so the next step seems to be the tabulation of the rainfall into shorter periods to try and determine the exact time during which rainfall has its greatest effect on the corn yield. Therefore, the average yield of corn for the three counties of Franklin, Madison, and Pickaway, in central Ohio, has been calculated and the average rainfall for eighteen coop- erative stations in and around these counties. The period covered was from 1891 to 1910, inclusive, and it is believed that a correlation with the averages obtained in this manner has a high degree of accuracy. The correlation was made for each ten, twenty, thirty, forty, and fifty days, as shown by the following tables: Table 12. — Relation Between Rainfall and Yield of Corn in Central Ohio for 10-day Periods, 1891 to 1910 Correlation Periods coefficient r June 1 to 10 —0.09. June 11 to 20 +0. 12. June 21 to 30 —0.04. July 1 to 10 +0.16. July 11 to 20 +0.36. July 21 to 31 +0.36. August 1 to 10 +0.52. August 11 to 20 +0.29. August 21 to 31 —0.06. 373. August 1 to 10 most important. — This table seems to show plainly that the ten-day period from August 1 to 10 has the greatest influence on the yield of corn in central Ohio. The probable error for that correlation coefficient is =1=0.11, which is fairly low. n,t Probable error ±0. 13 . . . ±0. 13 ; ±0. 11 .... =^0. 14 WEATHER AND YIELD OF GRAINS 159 Table 13. — Relation Between Rainfall and Yield of Corn in Central Ohio for 20-day Periods, 1891 to 1910 Correlation Periods coefficient Probable error r June 1 to 20 +0.03 June 11 to 30 —0.10 June 21 to July 10 +0.07 — July 1 to 20 +0.36 ±0.13 July 11 to 31 +0.41 ±0.13 July 21 to August 10 +0.50 ±0.11 August 1 to 20 +0.45 ±0.11 August 11 to 31 +0.20 ±0.15 The highest value of r in this table is +0.50 from July 21 to August 10, and this is about five times the probable error. Table 14. — Relation Between Rainfall and Yield of Corn in Central Ohio for 30-day Periods, 1891 to 1910 Correlation Periods coefficient Probable error June 1 to 30 —0.02 June 11 to July 10 +0. 11 June 21 to July 20 +0.26 ±0.14 July 1 to 31 +0.43 ±0.13 July 11 to August 10 +0.49 ±0. 11 July 21 to August 20 +0.48 =^0. 11 August 1 to 31 +0.37 ±0. 13 374. Thirty days from July 11 to August 10 most impor- tant. — Here the greatest coefficient is for the period July 11 to August 10, when r is +0.49, and the probable error is ±0.11. These last three tables seem to show that the rain- fall before July 10 does not have a very great effect in varying the yield of corn. Also that the variations in the rainfall after August 31 need not be taken very seriously into account. The tables show further that the congelation co- efficient for the ten days of August 1 to 10 is higher than for any twenty- or thirty -day period, although the difference is slight. 160 AGRICULTURAL METEOROLOGY Table 15. — Relation Between Rainfall and the Yield of Corn IN Central Ohio for 40-day Periods, 1891 to 1910 Correlation Periods coefficient Probable error r June 1 to July 10 +0.07 ^_ June 11 to July 20 +0.24 • June 21 to July 31 +0.36 ±0.13 July 1 to August 10 +0.53 ±0.11 July 11 to August 20 +0.60 ±0.10 July 21 to August 31 +0.52 ±0.11 There seems little question in this table of the dominating influence of the rainfall during the period from July 1 1 to Au- gust 20. This correlation coefficient of +0.60 is six times the probable error. Table 16. — Relation Between Rainfall and the Yield op Corn in Central Ohio for 50-day Periods, 1891 to 1910 Correlation Periods coefficient Probable error r June 1 to July 20 +0. 17 June 11 to July 31 +0.36 ±0.13 June 21 to August 10 +0.49 ±0.11 July 1 to August 20 +0 . 59 ±0 . 10 July 11 to August 31 +0.55 ±0.10 The correlation coefficient from July 1 to August 20 in this table is +0.59 and is slightly less than six times the probable error. It is believed that the district covered by the yield and rain- fall figures in Tables 11 to 16 makes them very reliable and that the values may be taken as a standard for this sec- tion of the country. Similar tables should be worked out for other districts, however, as the correlations might vary under different distribution of rainfall or different temperature and sunshine. 375. Weather effects during different periods of develop- ment. — After showing the relation between the corn yield WEATHER AND YIELD OF GRAINS 161 and a single element, the rainfall, during certain definite pe- riods, the question naturally arises as to what is the effect of all the elements, i. e., the "weather," during different periods of development of the corn plant. This can be answered by a study of certain data that have been compiled at Wauseon, Fulton County, Ohio. In Table 17 there have been entered certain important data relating to corn growth and development from 1883 to 1912 as taken from the records of Mikesell. As will be seen, they cover the dates planted, dates that plants appear above ground, dates in blossom, and the dates ripe, together with a statement of the quantity and quality of the crop. From 1883 to 1901 the dates are for operations on his own farm, and during the balance of the period for certain nearby fields, the same field being used for the entire season. The average dates and periods of development are given at the bottom of the table. 376. Thermal and rainfall constants at Wauseon, Ohio.— Thermal and rainfall constants have been worked out for the different stages of growth of corn at Wauseon, Ohio, for 1883 to 1912, and appear in Table 18. In addition, the amount of available heat and the rainfall for ten days before the date of planting was determined and appears in the table. This table should be studied in connection with the data in Table 17 for the dates of planting, blossoming, and so on, and the number of days between these dates during dif- ferent years. 377. The average date for planting com is May 14, and the average number of diiys for the plants to appear above the ground is nine. Table 18 shows that the average to- tal number of thermal constant degrees during this period has been 143°, and the average rainfall 1 inch. The average time from the date the plants appear above the ground until they are in blossom is sixty-two days, and the thermal constant averages 1,599°; the rainfall averages 7.4 inches. The aver- age date when the corn is in blossom at Wauseon is July 25, although this date has varied between July 10 and August 6. The average date when the corn has ripened is September 13; or fifty days after the tihie of blossoming. The average ther- mal constant during this time is 1,337°, and the average rain- fall 4.6 inches. Table 17. — Phenological Dates and Data for Growth of Corn AT Wauseon, Ohio, 1883 to 1912, by Thomas Mikesell (Lat., 41° 35' N.; Long., 84° 07' E.; alt. 780 ft., A. M. 8. L.) ll - 1 o ?i, ;s e ^ S §i 1 ^ i a 1 ^ Date '^ 1 ^? '^^ S ( Quality Year Date above CO S Date in §.1 Date It 5- of planted ground 5a blossom qI ripe Qa ^ crop 1883 May 12 May 25 13 July 29 65 Oct. 10 73 60 Poor 1884 16 24 8 24 61 Sept. 15 53 90 Good 1885 18 25 7 23 59 26 65 65 Fair 1886 11 19 8 17 59 15 00 85 Good 1887 20 25 5 24 60 15 53 60 Fair 1888 15 25 10 25 61 20 57 75 Fair 1889 15 23 8 Aug. 3 72 30 58 85 Good 1890 27 June 1 5 July 26 55 20 56 50 Fair 1891 12 May 22 10 27 66 18 53 60 Good 1892 June 18 June 23 5 Aug. 6 44 25 50 60 Fair 1893 May 18 May 28 10 July 25 58 12 49 60 Good 1894 1 10 9 17 68 Aug. 30 44 60 Fair 1895 1 7 6 22 76 Sept. 10 50 80 Good 1896 9 14 5 10 57 Aug. 30 51 100 Good 1897 22 June 5 14 20 45 Sept. 12 54 80 Good 1898 18 May 25 7 20 56 Aug. 31 42 1899 18 27 9 17 51 30 44 90 Good 1900 Sept. 6 1901 May 12 27 15 18 52 5 49 1902 1 3 1903 1904 7 17 10 25 69 10 47 80 Good 1905 9 15 6 18 64 Aug. 30 43 75 Good 1906 10 16 6 17 62 Sept. 10 55 80 Good 1907 April 26 6 10 30 85 3 35 75 Good 1908 May 21 28 7 30 63 15 47 80 Good 1909 14 21 7 Aug. 6 77 25 50 80 Good 1910 11 21 10 1 72 30 60 90 Fair 1911 10 17 7 July 20 64 8 50 80 Fair 1912 10 20 10 22 63 2 42 95 Good Aver. May 14 May 23 9 July 25 62 Sept. 13 50 76 1 Data for the years 1883 to 1901, inclusive, apply to Mikesell's own estate; data for 1902 to 1912 apply to certain nearby fields, the same field being used for the entire season. 162 Table 18. — Thermal Constants (Base 43'' F.) and Rainfall During the Growtu of Corn at Wauseon, Fulton Co., Ohio, 1883 to 1912 Thermal Rainfall Year f 1^ op 1 ■S 1' -2 C55 .1 i' II ••Si i 1 o o •S 'i ^ 1 II if tl 1 o 1 -F °F °F °F 0^ In In In In In In In 1883 139 141 1,583 1,264 270 290 0.6 2.7 13.7 6.1 0.7 3.7 0.0 1884 114 161 1,496 1,412 240 290 1.0 0.8 6.0 5.9 1.1 0.0 4.5 1885 114 147 1,520 1,432 330 340 0.1 1.6 6.6 8.4 1.8 0.2 2.6 1886 134 128 1,477 1,565 290 260 0.9 0.9 2.8 5.5 T T 0.2 1887 205 131 1,693 1,371 350 330 0.1 1.4 8.4 1.9 1.0 1.0 0.0 1888 128 110 1,600 1,410 270 320 1.4 0.4 5.6 2.7 0.1 0.1 0.4 1889 250 143 1,649 1,239 250 240 1.3 0.4 15.3 2.3 1.0 1.6 0.9 1890 167 131 1,365 1,330 270 360 1.1 T 4.4 6.3 T T T 1891 103 148 1,568 1,366 200 250 0.4 0.6 6.6 4.0 0.4 0.4 0.4 1892 318 165 1,253 1,238 310 310 1.0 1.2 5.3 6.2 0.3 1.2 T 1893 140 163 1,634 1,411 300 300 1.0 0.3 8.4 1.4 0.4 1.0 0.4 1894 139 161 1,638 1,300 290 330 0.9 1.3 5.3 1.1 0.2 T 0.2 1895 157 175 1,919 1,428 250 270 T 1.2 2.3 3.8 0.7 0.2 0.5 1896 235 154 1,443 1,490 280 290 0.2 0.6 8.2 13.8 4.0 1.4 6.4 1897 153 186 1,232 1,486 290 320 1.0 1.2 5.4 3.5 1.0 1.7 1.3 1898 150 177 1,566 1,25C . . . 1.7 1.4 6.1 4.7 . . . 1899 109 154 1,478 1,344 290 320 1.4 1.2 4.7 2.3 2^8 2.2 i!2 1900 1901 151 201 1,468 1,54G ... o's 1.8 8.3 '2'2 . . . . 1902 1903 1904 146 109 1,637 1,140 290 270 0.1 o'o 6.5 '3^6 0'8 L6 0^6 1905 142 97 1,526 1,210 290 270 0.8 3.3 10.2 2.9 0.1 0.1 0.2 1906 91 127 1,574 1,607 300 280 0.6 0.4 6.8 6.1 0.3 2.3 0.2 1907 -25 36 1,702 897 290 160 0.4 0.8 10.7 3.3 1.4 1.3 2.0 1908 213 199 1,735 1,229 300 300 2.6 0.4 9.6 3.4 0.0 2.1 0.2 1909 135 107 1,984 1,223 310 300 2.5 0.4 10.7 6.0 0.5 1.1 2.6 1910 78 114 1,811 1,453 290 260 1.0 0.7 6.6 6.9 0.1 3.4 T 1911 125 166 1,913 1,322 290 230 0.1 T 10.2 5.0 1.1 1.0 0.8 1912 168 123 1,645 1,107 300 270 0.8 2.2 5.3 5.1 0.6 0.8 0.8 Means 150 143 1,599 !,337 296 286 0.9 1.0 7.4 4.6 0.8 1.1 1.1 163 164 AGRICULTURAL METEOROLOGY Table 18 also gives the thermal and rainfall constants for ten days before blossoming and for ten days after blossom- ing, as well as the rainfall during the ten-day period from five days before to five days after blossoming. 378. Thermal constants and corn yield, Wauseon, Ohio. — In Table 19, the correlation coefficient has been given between the thermal constants during different periods of corn development and the percentage of a good crop, as re- ported by Mikesell. It is unfortunate that we do not have the yield of corn in bushels to the acre, yet believe that the percentage figures have been carefully considered by the ob-. server. Table 19. — Results of Correla.tion Between Thermal Constants AND Corn Yield, Wauseon, Ohio, 1883 to 1912 Correlation Probable Periods coefficient error r (1) For 10 days before planting — . 03 (2) From date of planting to date dt»ove ground —0.03 ■ (3) From date above ground to date of blos- soming +0.18 ±0.12 (4) From date of blossoming to date ripe . . . +0 . 08 (5) Daily mean temperature for 10 days be- fore blossoming — . 003 — (6) Daily mean temperature for 10 days after blossoming .' —0.28 ±0.10 There is a slight positive relation between the temperature from the date when the corn appears above the ground and the date of blossoming and the yield of corn, as well as a negative relation between the temperature for ten days after blossoming and the yield, but these correlation coefficients are all too low to be given any consideration. This table seems to show that there is little or no relation between the daily mean temperature and the yield of corn. 379. Rainfall constants and corn yield, Wauseon, Ohio. — In Table 20 the correlation coefficients between the yield of corn and the rainfall during the different periods of growth are shown. WEATHER AND YIELD OF GRAINS 165 Table 20. — Rerults of Correlation Between Rainfall and Corn Yield, Wauseon, Ohio, 1883 to 1912 Correlation Probable Correlation factors coefficient error r (1) For 10 (lays before planting +0.01 (2) From date of planting to date above ground — . 06 (3) From date above ground to date of blos- soming — . 03 — ■ ■ (4) From date of blossoming to date ripe. . . +0.29 ±0.11 (5) From 5 days before blossoming to 5 days after blossoming +0.45 ±0. 10 (6) For 10 days before blossoming +0 . 20 (7) For 10 days after blossoming +0.74 =±=0.05 (8) For 20 days after blos.soming +0 . 57 ±0 . 08 (9) For 30 days after blossoming +0.46 ±0.09 The results from this table are very important. It seems to make plain that there is no relation between the variations in rainfall in the first part of the period of growth of the corn crop and the variations in the yield. The average date of blossoming as determined in Table 17, is July 25, or sixty- two days after the plants appear above the ground and seventy-one days after planting. The correlation coefficient for the first three items in Table 20 is much too near zero to receive consideration. The correlation coefficient in item 4 indicating the effect of the rainfall between the dates of blossoming and ripening is +0.29, but as this is only two and one-half times the probable error, even this is not very close. 380. Rainfall near the blossoming time important. — The value of the coefficient for the rainfall for ten days before the date of blossoming as stated in item 6 is also too low to be given serious consideration. In item 5, however, covering the time from five days before blossoming to five days after blossoming, the correlation coefficient is four times the prob- able error and a relation is apparently esta])lished. It is in item 7, however, that there is the highest correla- tion coefficient. This shows that the rainfall for the ten days after blossoming has the greatest effect on the yield of corn of any period in the development of the plant. This value is +0.74, and it is fifteen times the probable error. This coef- \ 166 AGRICULTURAL METEOROLOGY ficient is considerably higher than even that for the twenty or thirty days following the date of blossoming. In Tables 12 and 16, there were given ,the correlation coefficients for the rainfall for the state of Ohio as a whole, compared with the yield of corn, for arbitrary ten-, twenty-, and thirty- day periods. All near the average date of blossoming gave high values. These facts combined with the high value in item 7 of Table 20 go to show that the rainfall immediately after blossoming has a very dominating effect on the yield of corn. 381. Combined, effect of rainfall and temperature. — Item 7 in Table 20 indicates a direct relation between the rainfall for ten days after blossoming and the yield of corn, and item 6 in Table 19 seems to show an opposite effect of the temperature on the yield during the same period. 382. Effective rainfalls. — It is well known that small rainfalls during a drought may actually do more harm to a crop than good, because by merely wetting the surface of the ground an effective dust mulch may be destroyed and thus more water be lost to the crop by evaporation than has been gained by the shower. Or numerous light showers during the early growth of the corn, by merely wetting the surface may cause the plants to root near the surface where the soil will quickly dry out in later dry spells. In investigations of ac- cumulative effects of weather, it was found that when July was quite dry the final yield was greater if the previous June was moderately dry also. The rate of growth and develop- ment of corn plants have been determined with certain defi- nite amounts of water in the laboratory. But to try to answer the often repeated question as to just what rainfall amounts are actually beneficial or are most beneficial to the growing corn, the following plan has been adopted: The rainfall for a definite district and period is multiplied by the total number of days with a certain amount of rain, and divided by the whole number of days in the period. The equation is simple; — , where a is the total rainfall for the period, b the number of days with 0.10 inch, 0.20, 0.30 inch, and so on, rainfall or more, and c the total number of days in the period. In Table 21 the effective rainfall was determined by tak- ing the rainfall at Columbus, Ohio, for the fifty-one day pe- WEATHER AND YIELD OF GRAINS 167 viod from June twenty-one to August ten for twenty years, working out new factors in accordance with the formula as above, and correlating these new factors with the yield of corn in Franklin County, Ohio. This method shows whether a certain amount of rain is as effective coming in many small showers, as it is in a few heavy showers and it is accomplished by eliminating consideration of days with rainfalls below 0.25 inch. The general rule has been stated that for equal quantities of rain its value to agriculture increases as the number of rainy days diminishes, and on the other hand diminishes as the number of rainy days increases. This can be true, how- ever, only up to a certain point. Table 21. — Correlation Table for Determining the most Effec- tive Rainfall in the Yield of Corn in Columbus and Franklin County, Ohio Corrdnlion Prohable Correlation factor coefficient error r Kainfall for July and yield of com +0 . 48 ±0.11 Rainfall, June 21 to August 10, and yield of com +0.G0 ±0.10 Factor determined for the amounts given below as per formula and the yield of com Days with 0.01" or more +0 . 61 ±0 . 10 '' +0.61 ±0.10 " +0.61 ±0.10 '' +0.64 ±0.09 " +0.59 ±0.10 " +0.61 ±0.10 " +0.70 ±0.08 " +0.55 ±0.10 " +0.56 ±0.10 '' +0.57 ±0.10 " +0.38 ±0.13 '' +0.59 ±0.10 " +0.41 ±0.12 (( tc 0.10" a u 0.20" CC i( 0.25" (( (( 0.30" (( (C 0.40" (( le 0.50" " " 0.60" a (( 0.70" u u 0.75" a t( 0.80" CC CC 0.90" CC CC 1.00" 383. Rainfalls of 0.50 inch or more most effective. — This table indicates that rainfalls of 0.50 inch or more are the most effective in determining the yield. For fear that the results might be affected by taking the rainfall at only one station, 168 AGRICULTURAL METEOROLOGY similar correlations have been calculated for the yields in Franklin, Madison, and Pickaway counties, in central Ohio, and for the rainfall at all of the stations in and around those counties, eighteen in all, for the period from July 21 to August 10. The results follow in Table 22. Table 22. — Results from Correlations for most Effective Rainfalls, Central Ohio, 1891 to 1910 Correlation Probable Rainfall factors coefficient error r Rainfall, July 21 to August 10, and corn yield. +0.50 ±0.11 Factor determined for the amounts below as per formula and the yield of corn Days with 0.01" or more +0.44 ±0 12 U U Q_JQ// U U 0.20" " 0.25" '' 0.30" " 0.40" " 0.50" '' +0.51 ±0.11 +0.43 ±0.13 +0.49 ±0.11 +0.50 ±0.11 +0.47 ±0.11 +0.G4 ±0.09 The differences in the correlation coefficients for the lower rainfall amounts are not great and could be purely accidental. But the higher value of r for 0.50 inch or more corresponds to /^Af /ff^ J396 /897 /S3am9 /900 /90/ /90^ 1903 /904 J905 /906 f907 1908 Bushelt <^' \, \ ( \ / \ 1 \ ^4 W / Vs 1 1 '^ / \\ / \ ""^v. 1/ % / \' / \ ^^ X / \ "^^^ ^' \ \ / ."'''' '' ^"~- \\ / Corn Crc P V / ^a/nfa// \' / 1 \ f /^.T. Fig. 44. — Relation between the July rainfall and the yield of corn in Tennessee, 1894-1908. that determined in Table 21 and seems to show that one-half inch of rain is more beneficial than lesser amounts. 384. Rainfall and com in Tennessee. — Fig. 44 illustrates the relation between the rainfall for July and the yield ot corn WEATHER AND YIELD OF GRAINS 169 in Tennessee. In this state the corn tassels in July and is favorably affected by an abundance of rain as in other sec- tions. 385. The accumulated effect of the weather on the con- dition of corn in Iowa and Missouri in 1917 is shown in Fig. 45. The spring and early summer of 1917 were cold and wet, but on July 1 the condition of the crop as reported by the Bu- No. 3. Iowa and Mi ssoori. ■ ^1 llliiiillll S 2.6 _s- -^ 1 1 rr M f f 1 1 r 1 2.4 J 2.2 L - 2.0 1 1.8 , 5 ^ L4 - Id 8 1.2 -^, ■ 0.6 - !^ = **■".. I . . . Percentage of e tio Ji^M [a — r.Jr-l-»— }^ 1 r^TO^m 80 75 Fig. 45. — Diagram showing the effect of the weather on the condition of corn in Iowa and Missouri in 1917. reau of Crop Estimates of the Department of Agriculture was not far from the ten-year average in all of the principal corn- growing states. Dry and warm weather the latter part of June and most of July lowered the prospect in the western Plains region, but in Iowa and Missouri, although drier than normal, the lack of moisture was not sufficient to lower the condition. 386. Weather and com, 1918.— Fig. 46 shows that warm and wet weather in May and the first of June, 1918, was favor- able for corn in Missouri and the condition was well above the 170 AGRICULTURAL METEOROLOGY ten-year average the first of July. From the week beginning July 3 until about the middle of August, however, the precip- itation was constantly deficient in Missouri, four of the weeks being practically without rain. As a result, together with the high temperature in August, there was a marked deterioration in the condition of corn through July and August in this state. No. 2. Ui830un. u Vi A 2-6 1 2.4 1 2.2 •3 2.0 g L8 5 !•' h. ^* 1 " 1 »•» * 0.8 0.6 0,4 0.2 fi +8° 1 -t-eo 1 +20 1 ^ 1 -20 2 - 4" 1 -^ t? -10° 1 fl d 8 ^ S 'xU ■4"¥ .. — - .. _"^ ^f *^ — ,XII" T — — ' itt T " fl - 1 m Ej lit s 1 T 1 ■ 1 k III ' £ 1 1 . :i I 1 1 • i i ±t± -f- o« 120 j^ ^ A> Z!^ 116 / ^-^ /- ^ "^^ 110 z: 2 V r \ 1 106 z^ V. 1 ^ \ 1 -inn r"^ ^"^ A \ % \/ \- s ^ J x S N TT \ 80 SL ^ 75 \ Fig. 46. — Diagram showing the effect of the weather on the condition of corn in Missouri in 1918. The condition of corn on the first of each month, as compared with a ten-year average, expressed in percentages, is indicated by the dots which are connected by broken lines. The significance of the temperature and rainfall values is explained under Fig. 34. 387. Spring frosts and com. — Early planted corn makes a slow growth and hence is not so susceptible to frost damage as that planted later and which may be growing more rapidly when a late frost occurs. Very young corn may be cut by frost without serious injury to the plants. 388. Fall frost damage. — Frost in the fall is seldom early enough or covers sufficient territory to cause widespread loss WEATHER AND YIELD OF GRAINS 171 of the corn crop. Even if some fodder is frosted, a light or moderate frost may cause more rapid ripening. 389. Frost in 1917. — In 1917, however, a cold late spring and generally cool sunnncr was followed by unusual and severe frosts, the first early in September. As a result, no corn fully matured in northern North Dakota, Minnesota, and Wisconsin, and less than 50 per cent as far south as northern Ohio, Indiana, and Illinois, and in northeastern Iowa. In an average year, 90 per cent or more matures in the southern part of this area, and 50 to 75 per cent in that part of the district where none matured in 1917. 390. Freezing injury to seed corn. — The germ of a sound kernel of corn is an embryonic living plant with stalk, leaves, and root. When this living germ contains a large amount of moisture, some physical or chemical change is brought about by freezing which results in death. Corn containing 10 to 14 per cent of moisture will not be injured by any amount of winter cold, but when it contains 60 per cent it may be killed by a prolonged exposure to a temperature but slightly below freezing. In fact, a very close relation exists between the moisture-content of the kernel and the degree of cold re- quired to kill the germ. 391. Damage to seed com in 1917. — Some of the corn that was seemingly mature in 1917 was so full of moisture that while it showed a fairly high germination in the early winter, it was so injured by very cold weather later that the germination was greatly reduced. 392. Short periods of drought and pollination. — Corn has two kinds of flowers situated some distance apart and in a normal season these will both appear at the proper time for fertilization. Drought, however, often hastens the shedding of the pollen, but delays the appearance of the silk. In this case, the pollen is wasted before the silk appears, proper fertilization is pre- vented, and no amount of rain later can produce a good crop. Cold and wet weather retards or even prevents shedding of the pollen. 393. Temperature and growth. — Corn makes most of its growth during the season of highest temperature, and this growth is retarded by cool weather or cold nights. It re- quires its greatest moisture in the summer when droughts are 172 AGRICULTURAL METEOROLOGY liable to occur, and when rainfall is less effective on account of the greater evaporation due to high temperatures. 394. Drought and. transpiration. — The maximum trans- piration in corn is during the warmest part of the day. On days of extreme temperature in very dry spells, there may be an atmospheric demand of ten pounds of water from a single average corn plant during twenty-four hours, the greater part in the seven hours in the middle of the day. Such days are very critical for corn if there is not a sufficient amount of moisture in the soil to meet this demand. It is evident that a drought during a brief period may affect the yield more than can be overcome by abundant rains at other stages of its growth. 395. Rate of seeding. — When the hills of corn are 33^ feet apart, there will be a stand of 10,668 stalks to the acre if an average of three kernels to the hill germinate and grow, or 14,224 to the acre if four kernels grow in each hill. In field practice, it has been found that from 3,630 to 7,260 stalks to the acre are all that can be properly supplied with the mois- ture that is available in the average year. It is stated that the great corn crop raised in South Carolina a few years ago was planted at the rate of 30,000 stalks to the acre, and hap- pened to receive an abundant rainfall just at the right period of its growth. 396. Weather and com in the South Temperate zone. — The following extracts from the "Agricultural Gazette" of New South Wales, Vol. XXVI, are of decided interest as they substantiate the results of studies in the North Temperate zone : It is well known that there is a critical stage in the growth of maize called the "cobbing stage," during which absence of sufficient moisture has a marked effect on yield. It has been determined by considerable observation and by statistics that the yield of a maize crop is almost directly proportional to the amount of rain received by the crop for the three or four weeks following flowering, other factors, of course, being equal. Hot, blasting winds during flowering are known to have very in- jurious effects on fertilization, either scorching up the pollen so that it will not germinate, or drying out the silks to such an extent that they have not sufficient moisture to germinate the pollen grains. To avoid damage by these winds, it has been found advisable in maize growing WEATHER AND YIELD OF GRAINS 173 for grain on the Murrumbidgcc Irrigation Area to plant early varieties, either early in September or late in December, so that these crops do not tassel during the hotter months of the year — December to Feb- ruary, inclusive. When the flowering period extends regularly over some weeks, it is possible that the crop possesses an adaptability that will enable it to weather through a few days' scorching winds more successfully than if the flowering period is limited to a few days, as is the case with some varieties. The value of sunlight is so well known that it calls for little com- ment. Many maize growers have recently been allowing greater width between the rows, and many have a fancy for running the drills in a north and south direction, so that the maximum amount of sunshine reaches the plants. It is sufficient here to say that if enough sunlight does not reach the plants at the flowering stage, the size of the cobs and also their fertilization generally suffers. This is particularly ob- served to be the case in a thick stand in a very cloudy season. It has been stated by some writers on maize that a crop may be "starved for rain" during the early growth, and yet yield excellently if it gets sufficient rain during the late growth. It is admitted that one of the worst things that can happen to the maize crop is for it to get plenty of rain during the early stage and a dry time during the later stage, but there is no doubt that the best crops are produced when there is a sufficiency of rain throughout the growing period, although it is preferable to have a dry period during the early half of growth rather than during the later half. In fact, some farmers go so far as to say that it does a crop good to get a set-back during the early growth, and it may be said that this is desirable when the later growing period is unfavorable. OATS The oat plant is most at home in cool moist climates; it is one of the most important grain crops in the North Temper- ate zone. 397. Range in United States. — Oats are widely grown in this country, but about four-fifths of the crop is produced in an area from western New York westward along the lower Lakes to the central Missouri Valley. The centers of most intensive cultivation are in northeastern Illinois and north- western Iowa, as is shown by Fig^ 47. Spring oats are grown in this district. 398. Seeding and harvesting. — Spring oats are seeded in the late winter and very early spring, when the mean daily rise in temperature reaches 43° on an average. The crop is 174 AGRICULTURAL METEOROLOGY II yx ~ iiliiiliiiiili ^ 11 1 r «.« i- o g - .X - <= o r^j 2 o-' — ■ \ Iv A ' • '-v^^^\^ *< 5? a: OT 000 REA 1 ) TIM ARE, \W\^ ^v.r^-r'v./^^ Qo <«S yj ") 1 \ \_ * X" 5-^ \ ri ^■>— — S. T. V ^/^ T.\ X \ ' '•-'•'• •' C O ?!;!!!• Itt^ Si_jOj^\ 1 1 • ■^NJ * . .' '.'■." • ' \. r^ r:^ •••.r^i^ ii i|SI K^ ■. /S-pJ /^ ■^ e ? ^* 3 \ N. V ■^ v" • , ' • i o tr. *£*r llJ / N-, yf ^A^ i . / • • • • ■ ( o ( • ••.•". • pJ •..x^"^-^ < J -/I r^'. '■ '•■': • * \ q: o> • •. • .\; !^^. J^V""^ ■'■ . ' ■ ^ OO J-*A*'"'***^ "^ ^>^ N< ■W: :.*•::*.•;/ •*•■•■.••• V'" ■• •• ^T^J-^ <2 : - . ; V r-.."... •;.•:■;•■;::: J, ".;' \r^ / (0 . • • •''.•■.•':•■>• '••'■■'■■'(' ' '. ^^ H : < y^ O ! • .' , ••• r __ /^ I • /■ ' ^ '■■ ' ' 1 ■ 1, -> / . / • ■ / \ y^ iiiiiiiiiil / . _ !Csg;c'gS»^ = s ■/• ' / '/ / ,«-,^^^-,,v.-.^~ / 1 1 1 1 is 2Sisci~«3:c;:; l._^ JvT^'r] Jl 3- 5SSSSSg5="= 5 -i5l5:.^53.^ iiiiiiiiii ytlT''^ ■ 1. — "^ — L. /il s|s;||s;issi / ^^^'^"^t^^'H'^v^ ^ igsgsisi^.2 f i / / • • ^^^ III / y^""^ ^Nv> / *i '^ slSsiS^SSS / ■ •' / ^7 y^ ^1 <^ ' / { / y^ o^ :^xJi.=oiil >%^.. J /^ x'^ y^ \ C! flliiiiiii 1 ^"""-"'..^^^y^ _f 3 i| sgagssgsng 5 » ^ ~" ~' ~ -" -■ !!; ^- ^v^^^* . / '•'■' .^^ 2 ii ^"■""s. / » • •^■'''"'""''^ ~ ^^^-^.--^--^^''""'^^ T > i-e=^J^^-3 iaz^»zoJ.; ivo wn + AT ? ? f ■Z / +1 ' +. 1 •f-4 Fig. 48. — Effect of the rainfall and tem- perature in June on the yield of oats in IHinois, 1878-1915. WEATHER AND YIELD OF GRAINS 177 and below the normal six times. In the fourteen years with a deficient rain, the yield of oats was less than normal twelve times and above only twice. Cool weather is desirable in June in this state for the best yield of oats. 404. Illinois, 1878 to 1915. — June is also the most im- portant month in this state in the effect of weather on the yield of oats. Fig. 48 shows that cool and wet Junes have been followed by yields above the normal 82 per cent of the time, while dry and warm Junes have been followed by good yields only 18 per cent. None of the other months shows a marked relation. 405. Iowa. — April is an important ''weather" month for oats in Iowa. During the period from 1890 to 1915 when April was warm and dry, the yield of oats was above the nor- mal 73 per cent of the time and when the month was cool and wet the yield was below the normal 71 per cent. As seeding becomes general in this state in the first part of April, this in- dicates the importance of a good seed-bed. There is some evidence that the temperature in June and July should be slightly below the normal for the best yield of oats in Iowa. 406. Maryland. — Seed formation of spring oats is pre- vented in southeastern Maryland if there is hot humid weather at heading time. 407. North Dakota, 1892-1915.— Oats are seeded in North Dakota generally later than about the middle of April and are not harvested until August. This later season of crop development makes the critical period for oats extend into July although June is an important month. During the pe- riod from 1892 to 1915 whenever June was warm and dry, the yield of oats was below the normal in every instance and when cool and wet the yield was above the normal 90 per cent of the time. The yield of oats in bushels per acre is lower in North Dakota than in the upper Mississippi valley and Lake region because of the lighter rainfall and the later critical period of growth. Hot weather in July may cause blighting and rust development. 408. Wisconsin. — The following shows the correlation between the weather and the yield of oats in Wisconsin for the period from 1891 to 1917: 178 AGRICULTURAL METEOROLOGY Table 24. — Correlation between Temperature and Rainfall and Yield of Oats in Wisconsin, 1891 to 1917 Month Rainfall Correlation Probable Temperature Correlation Probable coefficient error coefficient error April May June — 0.31 +0.23 +0.12 =t0.12 ±0.12 +0.39 ±0.11 1 ond -0.47 ±0.10 409. Critical period for oats. — Notwithstanding the fact that oats are a cool weather crop and that spring oats should be seeded as early as practicable, the facts given above show that the temperature should be above the normal for the sea- son and locality and the precipitation below the normal to produce the best conditions for seeding and the germination of the grain. While the heads are forming, however, and the grain being developed, the crop must have cool and moderately wet weather to produce the best yields. Cool weather favors the ripening of the grain, while the crop is often materially re- duced by a few hot days when it is near maturity. 410. Weather and. oats in Russia. — Brounoff found that the critical period of oats in respect to moisture is within the ten-day period before heading. Oats were seeded in his in- vestigations early in April, headed the last of June, and were harvested the last of July. An abundance of moisture was found necessary in June when the plants ''are ready to de- velop a great number of new important vegetative organs." He found further that cold weather and morning frosts from the time of seeding up to the appearance of tillers were not seriously damaging, but contribute to the formation of strong and thick roots. After tillering, however, frosts were very injurious. He states that hot days with mean daily tem- peratures above 75° and with maximum temperatures above 86° between the ''earing" and milk stage endangered the yield of oats, especially if there were a number of such days in succession. A similar temperature after the milk stage may cause a falling out of the grains. 411. In England. — The following is quoted from R. H. Hooker and agrees with the results obtained in the United States : WEATHER AND YIELD OF GRAINS 179 Oats are similar to barley inasmuch as they urgently require a cool summer; the partial coefficients between oats and temperature being almost identical with those of barley in the 17th-36th weeks. But they differ from barley in requiring rain in the spring; in fact for the spring (season) the coefficient with rainfall (+0.70) is just above the summer coefficient with temperature (—0.69). Before harvest (25th to 32nd week), however, they would seem to like dry weather. There are some suggestive negative coefficients with rainfall during autumn. Can they mean that seed does not keep well during a damp autumn? The coefficients with the preceding summer all seem insignificant. Comparing the three cereals, it is noteworthy that with barley and oats spring and summer are of preponderating importance, seed-time being relatively unimportant: with wheat, on the other hand, there are several different periods which may materially affect the crop, the seed- time being the most influential. RICE Rice is a tropical cereal and thrives best in regions of great heat, heavy rainfall, and high humidity; but can be success- fully grown in the warmer parts of the temperate zone. Fully 93 per cent of the world's production is raised in southern and eastern Asia and the nearby islands. 412. Rice districts in the United States. — The most im- portant rice-growing district in the United States is in south- ern Louisiana and southeastern Texas, but other locations where the crop is cultivated to a considerable extent are in north-central California, eastern Arkansas and in the coast counties of South Carolina and Georgia. 413. Temperature and rice. — The great part of the crop is cultivated where the mean summer temperature is over 75° to 77°, although certain varieties are grown in Japan where the average is not over 70°. The maximum temperature lim- its are unknown, but the minimum limits are of great impor- tance. At temperatures lower than 46° to 50°, the tender leaves are partially arrested in growth and the greener parts of the stem turn yellow. The maximum rate of growth cor- responds to the highest minimum temperature and where there is a lowering of the minimum below the critical point there is a decrease in all its functional activities. It requires a growing season of at least 135 days. 414. Water requirement. — The largest rice regions have an annual rainfall of 50 inches, and a rainfall of 5 inches a month during the growing season. Irrigation is necessary 180 AGRICULTURAL METEOROLOGY f in the United States. In the Atlantic Coast districts the fields are flooded as soon as the seed is planted to cause sprouting; this is called the "sprout" flood.. The water remains from 6 to 12 inches deep over the fields until the small white sprouts show through the hulls. The fields are then drained to prevent rotting. A little later the second flooding called the ''point" or ''stretch" flood is given. After the plants are about 6 inches tall, the water level is lowered to about 4 inches deep and it is held at this depth from fifteen to thirty days. The average length of the irrigation season in the Mis- sissippi Valley and Texas is about eighty-six days. RYE Rye is adapted to a wide range of climate, but by nature it is a plant of high latitudes and cool climates. Fully 99 per cent of the crop in the United States is fall-sown. 415. Range in the United States. — The bulk of the pres- ent rye production in the United States is from New Jersey and New York westward to North Dakota. The northern limit follows rather closely the mean winter temperature line of 15° in Wisconsin and Michigan, but in northwestern Min- nesota it is grown where the mean winter temperature is about zero and a temperature of 40° below zero is occasion- ally reached. 416. Weather and rye. — Rye may be sown later in the fall than wheat, as it will germinate more quickly and at a lower temperature. It will germinate and grow with a tem- perature but little above freezing, when wheat would be prac- tically at a standstill. Rye in the milk is not damaged by light frosts. 417. Rye in Wisconsin. — A correlation of weather with the yield of rye in Wisconsin for the period from 1891 to 1917 shows the following: Table 25. — Correlations between Temperature and Rainfall and Yield of Rye in Wisconsin, 1891 to 1917 Month April May June Rainfall Correlation coefficient -0.40 +0.29 -0.14 Probable error ±0.11 ±0.12 Tem,perafA Correlation coefficient +0.14 —0.11 -0.43 lire Probable error ±0.11 WEATHER AND YIELD OF GRAINS 181 Tliis indicates that dry weather in April and cool weather in June are the important factors in the growth of rye in Wis- consin. Experiments in Russia showed that for the best develop- ment rye needs abundant moisture and heat before the forma- tion of the heads; cool and damp weather during the forma- tion of the heads; moderate temperature and dry weather during blooming as it does not fill well if it rains while in bloom, and moist and warm weather during the ripening pe- riod. GRAIN SORGHUMS Grain sorghums are of tropical origin and are at home in regions with a rather dry, hot, and sunshiny climate. They are able either to resist or escape drought damage by their ability to suspend growth during periods of protracted drought without being destroyed, recovering and making good growth and fair yield when rain comes. Broom-corn is most profitable where there is but little rain at the time of har- vest as otherwise the heads are apt to be discolored. 418. Temperature and sorghums. — The grain sorghums are sensitive to low temperatures and will not do well at high altitudes because of cool nights. The northern or upper limit of Kafir is a mean summer temperature of about 75° and that of milo is about 70°. 419. Range in the United States. — The lower Great Plains is the home of most of the grain sorghums raised in this coun- try. In that region the summer temperatures are high, the percentage of possible sunshine great, the annual rainfall from 15 to 30 inches, and the frequent summer droughts are in- tensified by hot winds and excessive evaporation. The bulk of the crop is within the rainfall lines of 15 to 30 inches. WHEAT Wheat is the great bread cereal of the moderate temperate climates. In prehistoric times it had spread over Asia and Europe. Wheat has been found in tlie vegetable remains of the Lake Dwellers, and grains in the tombs and illustrations in the bas-reliefs on monuments show that it was raised in Egypt three or four thousand years before Christ. 420. Range. — Wheat is grown in Europe as far north as latitude 65°; in North America, to 50° north latitude; and in 182 AGRICULTURAL METEOROLOGY WEATHER AND YIELD OF GRAINS 183 South America and Australia nearly to 45° south latitude. It is raised within the tropics in Mexico, the Philippines, Egypt, India, and central Africa. 421. In the United States.— Figs. 49 and 50 show the distribution of wheat in the United States. These make plain that the most important center of winter wheat produc- tion is in west-central Kansas, and of spring wheat in nor- thern and eastern North Dakota and northeastern South Da- kota. 422. Distribution as affected by temperature. — The di- viding line between the principal spring and winter wheat- producing areas east of the Rockies agrees closely with the mean winter temperature line of 20° or the mean daily mini- mum temperature line of 10°. The southern border of the winter wheat belt agrees closely with the isotherm of 68° for the two months preceding the date of harvesting. The nor- thern limit of spring wheat agrees approximately with the mean summer temperature of 58°, which is found in the Uni- ted States only in the western mountains. Wheat will yield a crop, except in unusual years, at elevations up to 8,000 feet in the central Rocky Mountain regions where the mean tem- perature for the year is not below 38°, and where the mean for the summer season is not below 58°. In India the soil tem- perature at seeding time is very important in the production of winter wheat. When sown too early while the ground is warm, plants may start well but will soon decay and be at- tacked by white ants. It is considered safe to seed when the temperature of the soil has fallen to about 25° C. (77° F.) but not when it is as high as about 30° C. (86° F.). 423. Distribution as affected by moisture. — Most of the important wheat districts of the world have an annual pre- cipitation of less than 30 inches. In Australia the main wheat- producing areas receive less than 20 inches of rain during the growing months and in New South Wales and Victoria the chief areas are where the winter rainfall is between 10 and 15 inches. The intensive winter wheat-producing areas in Kansas and Nebraska receive an annual rainfall of 20 to 30 inches, while in the central Mississippi and Ohio valleys the amounts are somewhat greater. The most important spring wheat areas in South Dakota and Minnesota have an annual rainfall of 20 to 30 inches, while in most of North Dakota the 184 AGRICULTURAL METEOROLOGY WEATHER AND YIELD OF GRAINS 185 fall is between 15 and 20 inches. In this state, however, about one-third of the annual rainfall is received during the three spring months and fully one-half of the annual fall comes during March to June, inclusive. The successful growth of wheat is not limited by heavj^ rains, but other crops are usually found to be more profitable in regions of heavier rains, and, as in our southern states, where the annual rainfall is 45 inches or more, rusts and fun- gus diseases are prevalent due to warm and moist springs. It has been found in India that good soil aeration, by means of which the soil organisms and the roots of the wheat plant can obtain abundant oxygen, is quite as important as the water supply. It seems that any interference with aeration at ripening time prevents maturing and tends to increase rust attacks. In general, a hot dry climate produces a fine-stemmed plant the grain of which is hard, glassy, and rich in nitrogen, while a cool moist climate produces a coarser-stemmed plant with the grains relatively soft and mealy and poor in nitro- gen. 424. Dates of seeding and harvesting. — The work of seeding and harvesting wheat is being carried on in some parts of the world during every month of the year, as is shown by the following table: Table 26. — Where Wheat is Being Harvested Month Country January Australia, New Zealand, Chili. February India, Egypt. March India, Egypt. April Africa, Asia, Mexico, Cuba. May Central Asia, China, Japan, extreme south- em United States. June Southern Europe, southern and central United States. July Central Europe, Northern United States, Canada. August Western Europe, Canada, extreme northern United States. September Northern Europe. October Northern Europe. November Western and southern South America. December Southern South America. 186 AGRICULTURAL METEOROLOGY Figs. 51 and 52 show the average dates of beginning of seed- ing and harvesting spring wheat in the United States, and Figs. 53 and 54 similar data for winter wheat. Winter wheat can be seeded too early and also too late for the best results, while between there is an optimum or best date for seeding in an average year. 425. The best date to seed winter wheat. — There is usu- ally greater danger by winter killing of late-sown wheat than Fig. 51. — Average date when the seeding of spring wheat begins. of early-sown, especially with a dry fall, as there may be a failure to establish a good root system ; the probablity of good tillering is also reduced. On the other hand, wheat seeded too early is subject to damage by the hessian fly in some districts. Fig. 55 shows the date for seeding which will, in the normal year, reduce or avoid injury by the hessian fly and probably give a greater yield. By comparing the charts, it will be seen that the safest date in much of the winter wheat belt is from ten to twenty days later than the date when seeding usually begins. The state entomologist should be consulted, how- ever, as to the prevalence of the hessian fly and its activities. 426. Important periods of growth. — Well-recognized stages in the development of grains are germination, tiller- WEATHER AND YIELD OF GRAINS 187 188 AGRICULTURAL METEOROLOGY ing, jointing, heading, blossoming, and ripening. Records covering thirty years show that in northwestern Ohio the length of the period from seeding of winter wheat until the plants appear averages nine days; from the appearance above ground until blossoming 253 days; from blossoming until ripe twenty-six days. 427. Fruiting period. — In Kansas the fruiting period or average length of time between heading and ripening of fif- Fig. 53. — Average date when the seeding of winter wheat begins, teen varieties of winter wheat is twenty-nine days. The fruit- ing period varies for the different varieties from twenty-five to thirty-four days. In Ohio the average time between head- ing and ripening of one variety is thirty-six days. The fruiting period for four varieties of spring wheat in North Dakota averages thirty-five days. 428. Days from sowing to harvesting. — The total num- ber of days from sowing to harvesting east of the Rocky WEATHER AND YIELD OF GRAINS 189 190 AGRICULTURAL METEOROLOGY .a: 1! 11 3 ?55;;5SSRsas 1 9/10 9/14 9/19 9/24 9/30 I 9/4 9/9 9/14 9/19 9/24 9/29 10/5 S 1 1 1 |.| S 1 1 1 I f i 1 § 1 1 II :C¥ WEATHER AND YIELD OF GRAINS 191 Mountains varies from 250 to 290 days for winter wheat, and 120 to 130 days for spring wheat. The time for spring wheat is from 130 to 180 days in the Pacific states. Some varieties of spring wheat will mature grain in 100 days at Fairbanks, Alaska, two degrees from the Arctic Circle. 429. Critical periods of growth. — All authorities agree that the wheat plant must have an abundance of moisture at the heading stage. Some would place the most critical stage just as the plants are beginning to head, others between the boot and bloom periods and still others between the bloom and milk. It was found in Utah that the period prior to the boot stage is very critical. If the plant is injured by drought at this time, it does not recover even if given water later; the yield of grain is affected more than the yield of straw. High temperature and lack of moisture while in bloom produce sterile heads. 430. Moisture and wheat. — It is agreed by different in- vestigators that wheat needs only sufficient moisture during the first six weeks of its life to keep it growing vigorously. A strong root system is obtained by a moderate amount of moisture although it needs sufficient during its early stages of growth to induce tillering. It is advised in Utah to begin irrigation when the plants are 6 to 8 inches high and to stop at about the time that it comes into bloom. It was found in Nevada that the greater yields were obtained by a 6-inch irrigation before heading and a 12-inch after heading. During about forty to sixty days be- tween the first six weeks and the last three weeks of its growth, the plant should have its greatest moisture. Soft wheats are usually less able to endure drought, hot winds, and severe winter-killing than hard wheats. Hard wheats, for example, are best adapted to central and western Kansas, while soft wheat is better in eastern Kansas. Warm and wet weather in midsummer is likely to promote an epi- demic of rust. Rust is an injurious disease in the southeast- ern states and the factor that limits the successful culture in warm humid regions. 431. Weather and spring wheat. — Spring wheat is grown in regions where the winters are cold and comparatively dry, and where there is little snow for the protection of winter grains. Durum wheat is a sub-species that is adapted to re- 192 AGRICULTURAL METEOROLOGY '9'/}"/ 1161 9161 SI6I trl6l CI6I S/61 1161 0161 6061 9061 L06I 9061 SO 61 P06I C06I €061 1061 OOBI 669/ 968/ 169/ 969/ 968/ t'SB/ €68/ 268/ 169/ P/'/A §«»<<,e^««)>rjc\4 ■^. \ \ \ \ ^ - -^ <: -^ -^ ^ ^ - - - - - ■' / - - ^ ^ -- ^ ~- ., '' ---■ ^ ■^ "~ ■- \ - ~~ _, ^ - ^ ■~- V ^ ^ ^ \^ •. ^ < S- ^ -^ - ■T' ■^ \ S ! -~^ - ■^ -' - -^ \ "^ ^ ^ ^ .1^ ^ ^ -r T- r: rr -^ r^ ~k V ^ "^ \ \ — -■ -- "^ \ ^ N| - ■~ -_ ^ > \ 1 / ^ U,s........«.^».| o 3 WEATHER AND YIELD OF GRAINS 193 L;!K5 s o. , N «0 «j > Pj ^>«^ \ * 9lel - r-^ y<^^ - A^ .. ._ ^ ^^ \ --L" ;:::-4=- 806 f -* :►- $0$/ - ^-t'' ■' Q06I < "^ ' f06l ~^'~"~~ s t ^^ 7 Z06I \ \ 1061 <^ ^^ "■--.^^^ .--^""^ \ / 16 Bl ^^"^ 9681 y>^^ 9691 \ f69l — • "^ J^^^^^ t69l • % // ,„,_.__!:>f^ 'pi*!A 5;§55!iSS552| ^§0(Ots<0«>^ o 194 AGRICULTURAL METEOROLOGY gions of low rainfall, rather high summer temperatures, and when the loss of moisture by evaporation is rapid. These INS. 4 --3 -2 -1 1 2 3 4 5 IN5. 5 4 3 2 1 -1 -2 -3 -4 -5 lA /AR/^ A^D D^ RY. WAf^\ f AJVO WET V 5 4 3 2 1 -1 -2 -3 -4 -6 *. _ - \ ^ -MCAI V rrM P£/?A1 + + + + - 4!" ■ ' + + + I ?ffJLA ^D DR) COL 7LAf/D wsr. 1 \ 1 1 + 1 1 Fig. 58. — Combined effect of the temperature for June and the rain- fall for May and June on the yield of Spring wheat in North Dakota. 1891-1913. conditions are found in the northwestern Great Plains region. 432. Rainfall and spring wheat (Blair). — ^Figs. 56 and 57 show the relation between the rainfall during May and June WEATHER AND YIELD OF GRAINS 195 and the yield of spring wheat in North Dakota and South Dakota, respectively, as noted by T. A. Blair in 1913 and com- INS 4 -3 --^ -1 1 2 3 4 JNS. Y 5 4 3 2 1 -1 -2 -3 -4 -5 H 1 VARM 1 ANO D 1 RY. WAR A 't A/VO 1 WET. 5 4 3 2 J -1 -a -3 -4 -5 - — 1. VI VI c < -^SA/ W T£M PCRAl '-//ac' + + • ' + \ + + •t + -f L -ZP^Z A, 1 W DRy 1 COD L Af^D kKfT: 1 1 \ Fig. 59. — Combined effect of the temperature for June and the rain- fall for May and June on the yield of spring wheat in South Dakota, 1891-1913. pleted in 1918 by the author. These indicate that relatively dry weather in these states during May and June is almost invariably followed by a low yield of wheat, while an abundant rainfall is usually followed by a good yield. In Minnesota, on 196 AGRICULTURAL METEOROLOGY the other hand, there is Httle relation between the rainfall for May and June and the yield of wheat. 433. Temperature and spring wheat (Blair). — Figs. 58 and 59 indicate the effect of the rainfall for May and June and the temperature in June in varying the yield of spring wheat in North Dakota and South Dakota, respectively, for the pe- riod from 1891 to 1913, inclusive. 434. In North Dakota. — Fig. 58 shows that there were seven years during this period with the average temperature in June higher than the normal and that in every case the wheat yield was below the normal. There were fifteen years with the temperature lower than normal and in eleven of these the yields of wheat were above the normal. 435. In South Dakota. — Fig. 59 shows that there have been some good yields of wheat in South Dakota when June was warmer than normal, but when June was cool there was a greater percentage of good yields in this state than in North Dakota. In North Dakota there were ten years with June cool, and May and June wet, and in eight of these years the yield of wheat was greater than normal. In the six years in South Dakota when June was cool and May and June wet, every year gave a wheat yield above the normal. The following table gives the results of a correlation of weather with the yield of spring wheat: Table 27. — Correlation Coefficients Between Spring Wheat AND Rainfall and Temperature (T. A. Blair) North Dakota May and June May June July Rainfall Correlation Probable coefficient error {1892-1912) 0.63 ±0.09 0.48 ±0.11 0.35 ±0.13 0.30 ±0.13 Temperature Correlation Probable coefficient error (1892-1913) ' -0.39 ±0.12 0.02 ±0.14 — 0.67 ±0.08 -0.19 ±0.14 South Dakota May and June June (1891- 0.59 0.35 -1912) ±0.09 ±0.13 (1891-1913) — 0.62 ±0.09 -0.73 ±0.07 WEATHER AND YIELD OF GRAINS 197 Table 27. — Correlation Coefficients Between Spring Wheat AND Rainfall and Temperature (T. A. Blair) — Continued Rainfall Temperature Correlation Probable Correlation Probable coefficient error coefficient error Minnesota (1891-1912) May andJune —0.02 ±0.14 May and June (omitting 4 wet- test years) 0.26 ±0.13 North Dakota {1892-1917) May and June 0.61 ±0.08 June —0.45 ±0.11 South Dakota (1891-1917) May and June . 49 ±0.10 June —0.62 ±0.08 This table clearly shows the importance of cool weather in June and an abundance of moisture in May and June in the Dakotas. 436. Weather and spring wheat, 1918.— The effect of the weather in 1918 on the condition of spring wheat in the states of North Dakota and South Dakota is indicated in Fig. 60. The variation of the average monthly temperature and the total monthly rainfall from the normal is shown for the months of March to July in each state. The dots showing the condi- tion of spring wheat on June 1, as compared with the ten- year average are placed on the vertical line indicating the de- partures of the temperature and rainfall from the normal for the month of May, because the condition on June 1 is the result largely of the weather during May. For the same rea- son the dots for July 1 and August 1 are placed on the June and July lines, respectively. 437. Dry weather detrimental. — While there was a steady advance in the condition of wheat in South Dakota due to the generous rainfall throughout the season, it is evident that the deficient rainfall in June in North Dakota was responsi- ble for the lack of improvement in wheat in this state. Fre- quently the condition of this crop will be lowered to a marked 198 AGRICULTURAL METEOROLOGY A^O/?77y DAKOTA SOUTH DAKOTA Il 135 130 125 120 116 110 105 100 95 90 85 80 76 70 65 1 114^ 1 .MM ^ 6.0 . 6.5 1 5.0 § 4.5 •^. 4.0 1 3.5 1 3.0 •S 2.6 t 2.0 £ J.6 1.0 0.5 + 70 + 6P S + 40 1 + 3° 1 + 2° ■2 + 1° § 0- 1 -10 l'-2° 1-3° 5 -.40 -50 -80 -70 -8° ^ >, "^ — / s /- / / / / ^ / \ \ \ \ \ \ \ / \ \ { / \ / \ \ 4- \ -V "/ / \ .-^ ^— -H \ -~^^ X 'V / \ ■ \ ■ \ / \ \ / Fig. 60.— Effect of the weather on the condition of spring wheat in North Dakota and South Dakota in 1918. See the note under Fig. 34 for an explanation of the various hues, except that in Fig. 60 monthly instead of weekly rainfall and temperature conditions are indicated. WEATHER AND YIELD OF GRAINS 199 extent by insufficient moisture in two successive months, as was the case in Montana in 1917. 438. Weather and spring wheat in Manitoba, Canada. — From studies in the field in Manitoba, Connor found that ''if in the earher stages of growth it is cool and rainy, the head- ing will be delayed, and the yield will be heavy, but if warm and dry, heading is hastened and the yield will be light." He correlated the rainfall, range of temperature, and minimum temperature for successive thirty, sixty, ninety, and 120 day periods with the yield of spring wheat in Manitoba. The record covered the time from 1883 to 1917 and the highest correlation for the thirty-day period was for the third thirty days after seeding. The values were: Correlation Probable coefficient error Rainfall 0.42 ±0.11 Range of temperature — . 55 =t=o . 10 Minimum temperature — . 40 =*=0 . 12 He fixes the average time of the critical period as the last week in June and the first three weeks in July, and the crit- ical factor in wheat production in Manitoba the ''variability of early July weather." Winter wheat 439. The effect of weather on the yield of winter wheat. — The opinion is frequently expressed that the yield of winter wheat will be greatly affected by a warm or cold fall or win- ter, or by the temperature or rainfall of a single month or group of months. 440. Comparison of records in Ohio for fifty-four years. — In order to determine the ground for these opinions, correla- tions were made by the author between the weather factors for different periods and the yield of wheat in Ohio for the years from 1860 to 1913, inclusive. Table 28 shows the correlation coefficients between the average rainfall and temperature and the wheat yield for the state of Ohio. 200 AGRICULURAL METEOROLOGY Table 28- -Correlation OF Weather and Winter Wheat for the State OF Ohio, 1860 TO 1913 Precipitation Temperature Period Correlation Probable Correlation Probable coefficient error coefficient error September 0.04 ±0.09 0.16 ±0.09 October 0.16 ±0.09 0.09 ±0.09 November -0.02 ±0.09 0.14 ±0.09 December -0.17 ±0.09 0.05 ±0.09 January 0.09 ±0.09 0.21 ±0.09 February 0.01 ±0.09 0.26 ±0.08 March 0.06 ±0.09 0.46 ±0.07 April 0.02 ±0.09 — 0.10 ±0.09 May 0.02 ±0.09 -0.11 ±0.09 Autumn (Sept. to Nov.) 0.17 ±0.09 -0.03 ±0.09 Winter (Dec. to Feb.) -0.17 ±0.09 0.17 ±0.09 Spring ^ (March to May) 0.15 ±0.09 0.19 ±0.09 441. Precipitation and yield. — It will be seen that the correlation coefficient for rainfall is not high enough for any month or group of months to show any relation to the yield. In other words, the precipitation in Ohio is not the determin- ing factor in wheat yield. The precipitation is always suf- ficient and never so great as to affect the yield materially. 442. Temperature and yield. — The table also shows that the average temperature for a month, or for the group of months designated as "season," is not the all important factor in affecting the yield. 443. Mean temperature for March. — The most impor- tant weather factor in the table is the mean temperature for March. This gives a correlation coefficient slightly more than seven times the probable error and so can be said to have a marked influence on the yield. Fig. 61 gives the dot chart showing the relation between these factors. An inspection WEATHER AND YIELD OF GRAINS 201 of this chart makes plain that a warm March has been fol- lowed by a wheat yield above the normal twenty-one times out of twenty-four, or 88 per cent of the time. On the other hand, when March averages colder than the normal, the yield 4S 46 44 r i i 3a 32 30 28 • • • • • » • • • NORM 4Z. ^ • • • • 4 • • • • 1 • ' 1 AT. JO /8 /4 J6 YJELO OF WH£AT 18 20 22 Fig. 61. — Relation between the mean temperature for March and the yield of winter wheat, Ohio, 1860 to 1915. of wheat will be below the normal 63 per cent of the time. When March averaged 2 degrees a day or more above the nor- mal, the probability of the yield of wheat being above the normal in Ohio is 94 per cent, covering a period of fifty-six years. When March averages 2 degrees or more a day cooler 202 AGRICULTURAL METEOROLOGY than the normal, the probability of the wheat yield being above the normal is only 25 per cent. 444. March temperature in other states. — A similar study, though covering a shorter period of time, shows no such relation between the March temperature and wheat yield in Maryland and Delaware, Illinois, Nebraska, Iowa, Kentucky, or Oklahoma. 445. Effect of a snow cover. — A thorough study of the effect of a covering of snow during the winter as a whole and for different months, shows that a lack of snow on the ground with freezing and thawing weather is not such a detriment as has been believed. Instead, a lack of snow covering in Jan- uary seems to be beneficial, possibly because the earth thus settles around the roots and makes the plant better able to stand later unfavorable weather. The correlation coefficient for Wayne County, Ohio, between the number of days with- out snow cover and with the minimum temperature below freezing with the yield of wheat is -1-0.49, probable error =1=0.11. This is not conclusive, however, and should be given further study. 446. Snowfall as affecting wheat yield. — Snowfall is con- sidered favorable for winter wheat especially if it comes late in the spring. The following table seems to controvert this idea: Table 29. — Correlation Between Snowfall and the Yield of Wheat. 1892-1914 Period and place Correlation coefficient Probable error Jan., Fulton Co., Ohio 0.42 ±0.13 Feb., 0.12 ±0.15 March, " -0.84 ±0.04 " Wayne Co., " — 0.69 ±0.08 " Seneca Co., " -0.48 ±0.11 This indicates that a heavy snowfall in January is favor- able even though a large number of days with a snow cover- ing has an opposite effect. 447. Snowfall in March detrimental. — The most remark- able fact in this table is the evidence that snow falling in March is decidedly unfavorable to winter wheat as shown by the high negative value for the correlation coefficient. This WEATHER AND YIELD OF GRAINS 203 is brought out more clearly in Fig. 62 which shows the rela- tion between the snowfall for March and the yield of wheat in Fulton County, 1892 to 1914. In nearly every case when the snowfall is above the normal, the yield of wheat is corre- spondingly below. The figures at the left show both inches of snow and bushels of wheat. A similar correlation between the March snowfall and the wheat yield in other northern ' — — — — — — — « yv4? '«, \ ; \ \ 1 1 \ \ / \ / \ f \ » > / i \ / / \ 1 1 \ / ^ \ » / , / \ V ; 1 \ / , ■\ t \ ^ ^ \; \ / / 1 \ ; \ h *j \ \ // i\ 1 \ ^ \ 1 \ \^ \ ^ y ,■ / \ 1 \ k "•s ■ 1 \ 1 \ \ 1 -/o k * 1 / . / - Fig. 62. — Relation between the snowfall in March and the yield of winter wheat in Fulton County, Ohio, 1892-1914 Ohio counties gives much the same result, although no such marked effect has been found in other states. 448. In Indiana. — Cool weather during the month of April is decidedly favorable for winter wheat in Indiana. In the thirty-two years from 1887 to 1918, April was cooler than the normal eighteen times. Following the cool Aprils, the wheat yield was above the normal thirteen times and below five times. Following the fourteen warm Aprils, the yield was above the normal seven times and below seven times. 449. Cool and wet favorable in Indiana. — Of cool Aprils, the most beneficial appears to be those with an excess of pre- cipitation, as following nine cool and wet Aprils the yield of 204 AGRICULTURAL METEOROLOGY wheat was above the normal seven times and below twice. For the state, 2° in temperature and 1.25 inch of precip- itation, mark the average departures from the normal. Con- sidering departures greater than this as abnormal, it is found that only one wheat crop out of seven has been below the average after an abnormally cool April, also only one crop out of five has been below the normal following an abnor- mally wet April. 450. A cool May also beneficial in Indiana. — Of fifteen cool Mays, the wheat crop was above the average twelve times, eight of the twelve following cool wet Mays. 451. In Missouri. — The following tabulations show the relation between weather and the yield of wheat in Missouri for the months indicated, covering a period of thirty-one years : Table 30. — Correlation between Weather and Yield of Wheat in Missouri No. of yean March J Weather Yield above normal Below normal 8 7 8 8 warm and dry cold and dry warm and wet cold and wet 6 1 3 4 2 6 5 4 10 10 4 7 April warm and dry cold and dry warm and wet cold and wet 5 4 1 4 5 6 3 3 7 6 9 9 May warm and dry cold and dry warm and wet cold and wet 4 4 2 4 3 2 7 5 11 6 5 9 June warm and dry cold and dry warm and wet cold and wet 6 3 1 3 5 3 4 6 452. May warm and dry most favorable in Missouri. — If only these years are considered when the mean tempera- ture for May has varied 1.5° or more from the normal and WEATHER AND YIELD OF GRAINS 205 the precipitation 1.50 inches or more from the normal, the following results: Table 31. — Correlation between Weather in May and Yield of Winter Wheat May Years with yield Years Weather Above normal Below normal 4 warm and dry 4 1 cold and dry 1 3 warm and wet 3 3 cold and wet 1 2 The average yield of wheat in Missouri is 13 bushels to the acre. If only those years are considered when the yields va- ried 2.5 bushels or more from the normal, the following results are obtained: Table 32. — Correlation between Weather and Yield of Winter Wheat when Latter Varied 2.5 Bushels or more from Normal May Yield Years Weather A hove normal Below normal 3 warm and dry 3 3 cold and dry 2 1 6 warm and wet 1 5 1 cold and wet 1 These data seem to indicate that relatively warm and dry weather in May is needed in Missouri for the best yields of winter wheat. 453. In Kansas. — Investigations at the Fort Hays Ex- periment Station, Kansas, indicated that in western Kansas moisture is the limiting factor in the production of winter wheat. In a four-year stud}^, it was found that the yield of grain was in direct proportion to the supply of available mois- ture at seeding time. 454. Summer rain and yield of wheat in Kansas. — At the Fort Hays Station, which is not far from the center of the wheat area of the Plains districts, 75 per cent of the total an- nual rainfall is received between April 1 and September 30. At Wallace, Kansas, about 65 per cent of the annual fall comes in May, June, July, and August, while in Lincoln, Ne- braska, nearly 60 per cent falls in these four months. It was learned at Fort Hays that if the methods of handling the soil are such as to allow for the maximum absorption of the sum- 206 AGRICULTURAL METEOROLOGY mer rainfall, and to reduce the evaporation to a minimum, the yield of winter wheat will be affected to a marked degree. 455. Rainfall and temperature by months. — H. B. tan- ning made a careful study (unpublished) of the effect of the weather on the yield of wheat over an area including thirty- seven counties in the important wheat district of central Kan- sas. Dot charts were prepared for both temperature and 10 9 e 5 -J _1 < 5 Uu 2 ^^ 3 2 YIELD- BUSHELS PER ACRE | 6 7 8 9 10 II 12 13 14 I.S 16 17 18 19 20 • • • . • . • . ' • • • . Fig. 63. — Relation between the rainfall for July of one year and for April of the following spring and the yield of wheat for that season, Kansas 1893-1917. rainfall for each month and for groups of months from July preceding planting of wheat until the following June. 456. No temperature relation. — These charts showed no apparent relation between the mean temperature for any month and the wheat yield. In other words, the average tem- perature for any month does not vary enough from the nor- mal to have its favorable or unfavorable effects shown in the harvest often enough to be of importance. 457. Rainfall and yield in Kansas. — No appreciable re- lation was found between the yield and the rainfall for any of the nomths except for July preceding planting and for April preceding harvesting, and in these months the relation is slight. The yield increases in a general way as the rainfall for the preceding July increases, until the rainfall reaches WEATHER AND YIELD OF GRAINS 207 about 6 inches and the yield 13 bushels to the acre, but higher yields are always with less rainfall. The lowest and the high- est yields of wheat in central Kansas have occurred when the rainfall of the preceding July for that district was about one inch. Charts showing the yield and the rainfall for July and August, and July, August, and September also indicate a fairly regular increase in yield with increasing rainfall until about 13 or 14 bushels to the acre, and then higher yields have always been with less rainfall. 458. July and April combined. — Fig. 63 shows the rela- tion between the rainfall for July preceding and April of the year of harvest, and the yield of wheat in Kansas from 1893 to 1916-17. With three or four marked exceptions, there is a fairly close relation. The following statements of weather conditions favorable or unfavorable for winter wheat in Kansas, by months, are from S. D. Flora, meteorologist of the Weather Bureau: Table 33. — Conditions Favorable and Unfavorable to Winter Wheat in Kansas Month Condition favorable Condition unfavorable January Snow cover, abundance High winds, if dry. of moisture. Freezing and thawing without snow cover. February Same as January. March Cool and wet as it pro- Abnormally warm, es- motes stooling pecially with high winds; heaving. April Plenty of moisture and temperature near normal. May Warm and sunshiny Cold and wet favors black stem rust. June Warm and dry Excessively high tem- perature which shrivels the grain. July Warm. Wet delays harvest. August Dry for threshing, abun- dant moisture for preparing ground for next crop. September Prolonged dry spell. October Abundant moisture. November Abundant moisture; A cold period without December snow cover. snow. 208 AGRICULTURAL METEOROLOGY 459. In Iowa. — February is a very critical month for winter wheat in Iowa. A correlation between the weather and the surviving winter wheat acreage for twenty years gives the following result: Table 34. — Correlation between Weather aistd the Surviving Winter Wheat in Iowa February Weather Correlation coefficient Probable error Mean temperature 0.41 ±0 . 12 Average rainfall 0.46 ±0.12 Snowfall 0.36 ±0.12 The mean temperature was above the normal in February in the southern third of Iowa eight times and the surviving wheat acreage was above the normal every time. A warm and wet February is decidedly favorable for winter wheat in Iowa. 460. In Wisconsin. — A correlation between weather and winter wheat in Wisconsin for the period from 1891 to 1917 shows the following: Table 35. — Correlation between Weather and Winter Wheat in Wisconsin Month Precipitation Correlation Probable coefficient error April -0.14 Mav 0.14 ■ June -0.03 • Temperati ire Correlation Probable coefficient error 0.07 -0.12 —0.42 ±0.11 This indicates that a cool June is decidedly favorable for a good wheat yield in this state. 461. Winter-killing of grains. — Winter damage to fall- sown grains is usually grouped under four main heads: (1) heaving, (2) smothering, (3) direct effect of low tempera- tures on the plant tissue and protoplasm, and (4) physiologi- cal drought. 462. Heaving is one of the most common causes of dam- age especially on poorly drained, heavy soils. It occurs usu- ally in the spring, and is due to alternate freezing and thaw- WEATHER AND YIELD OF GRAINS 209 ing. The plants are lifted from the soil when it expands, and as a result the roots are broken and exposed to the air. Heav- ing is a common cause of winter-killing in the eastern part of the United States. 463. Smothering is believed to be a frequent cause of in- jury when the ground is covered with an ice sheet; instances have been reported where smothering has resulted from a very deep snow-cover. The damaging ice-sheet more fre- quently results from melted snow, although injury is some- times caused by a storm of sleet and rain, which freezes nearly as rapidly as it falls. 464. Freezing of plants. — There can be no doubt that plants are often killed by the direct effect of cold on the tissue, without heaving, smothering, or physiological drought tak- ing place. The injury usually increases with the degree of cold and its duration. The effect of a sudden freeze follow- ing a warm period is sometimes damaging, especially in the latter part of the winter or early in the spring, when a sharp drop in temperature follows a period of unusual mildness. 465. Physiological drought causes injury during dry spells in winter. Differences in resistance of certain cereals may perhaps be explained by their ability to absorb a larger amount of water from the soil in proportion to that transpired. 466. Winter wheat in 1919. — Fig. 64 shows the varying temperature and rainfall in Kansas and Indiana from August, 1918, to May, 1919, and the condition of winter wheat on the 1st of December, April, May, and June. Exceptionally fa- vorable weather for the growth of wheat prevailed in all sec- tions of the central wheat-growing area throughout the entire season. The soil was in excellent condition during the late summer and fall of 1918 for the preparation of seed-beds, germination of seed, and early growth of the young plants, and consequently the crop entered the winter in excellent condition with the roots well established. The winter was mild, with sufficient soil-moisture available, and the spring months were uniformly favorable for growth. The condition of the crop was exceptionally high on the first of April, 1919. 467. Yield disappointing. — The yield of winter wheat, however, did not come up to expectations, especially in the central and eastern portions of the belt, as compared with the indications a short time before harvest. It was quite disap- 210 AGRICULTURAL METEOROLOGY < < Q • d ■not? SiiasSgssffi ^ w CD* a. tfdV •yvw 8JJ - ~ s i ) " J ^ / / % f 1 / i S K \ \ / \ \ 03W ACN Idas -- - / ^ V \ s r- L ^ -^ V ^ i ,. - - ~ ^ ^ - •" L. _ < z: < d z: 00 5< S "s >l j *^ ^ L \ bYM ■ \ \ 1 aii - 1 \ \ \ J) \ k / } V s s t / /■ / /* ioo - ld3S / ? -^ V N, / ' •^ > ^ ^ . HINOW ++++++ 1 1 1 WEATHER AND YIELD OF GRAINS 211 pointing as to both quantity and quality. Under the influ- ence of persistent favorable growing weather, there was too rank straw growth at the expense of grain in many localities. There was considerable lodging and this combined with warm dry weather when the grain was in the milk stage and while ripening, resulted in many poorly filled heads and much shriveled grain. As harvest approached there was an increase in disease, particularly scab and rust. 468. Weather and hessian fly damage. — A correlation between the weather in September and October and the dam- age done by the hessian fly the following year in two counties in Ohio, during the period from 1895 to 1913, is shown below: Table 36. — Correlation between Weather and Hessian Fly Damage Rainfall Temperature Correlation Probable Correlation Probable coefficient error coefficient error Adams Co. September 0.02 =t0.15 0.24 ±0.14 October —0.13 ±0.15 0.53 ±0.11 Fulton Co. September —0.23 ±0.14 0.09 ±0.14 October 0.36 ±0.13 0.34 ±0.14 The only correlation that is high enough to be considered is with temperature in October in Adams County. This shows that a warm October is favorable for the development of the fly. 469. Rainfall and yield of wheat in Australia. — The aver- age yield of wheat in the state of Victoria for the twenty-five years from 1890 to 1914 was 9.1 bushels to the acre, while the average rainfall for the winter months. May to October, for 1890 to 1915 was 9.5 inches. A. E. V. Richardson has prepared the following graph, Fig. 65, to show the relation between the rainfall and the yield of winter wheat in that state. He states that this graph shows that there has been an improvement in cultural methods since the serious drought of 1902; that the best yields have been with a rainfall for the six months of between 10 and 13 inches; that with each inch of rainfall during the first twelve 212 AGRICULTURAL METEOROLOGY years, a yield of 0.77 bushels was harvested, while during the second twelve years the yield for each inch of rainfall was 1.12 bushels to the acre; and that it seems possible to calculate the probable yield of wheat by the' first of November. He shows the improvement in farming methods by the fact that during the first twelve years the line of yield was always GWHELS.r WHEAT " ~1 — ~ ~ — It. ' *t^ f. • 4 / A ■ 14 'i p< \ „ t•^■ i3 \ „ • / • / I ^ \ ■^ < IT ' ', \ r^ I 1 »\ / • \ / -N, ', t '° '\ / \'i / 1 \ ', ' / \ \ \ ' 1 • \ ', 7 \ ' / \ ^ \ » 1 ' ,' f \ \ / v / \ \ ; \ 7 - ■-, ' I ' M L ff \ 1 7 / \' ^ \ I 3 ** \ j a \ on 90 m '■ R KIN ^XL . 11 1 u o _2 t -A /fs ,' . ^^ I' 1' • • 1' •. . • • • • • • n * •• ' ^ • 1 • •• • . . . • ' . § $ 1 • • • • . Fig. 71. — Relation between the rainfall in May and the yield of hay (not including clover) in Ohio, 1858 to 1909. the country showed that the rainfall for May had a large in- fluence on the yield of hay. This and the further fact that the price of hay is influenced by the yield aided materially in a decision of the Inter-State Commerce Commissioners in a celebrated hay-rate case involving several million dollars. It has been stated that in order to produce a ton of dry hay on 238 AGRICULTURAL METEOROLOGY an acre of land, it is necessary that the growing grass pump up from that acre approximately 500 tons of water. 504. Hay in Ohio. — A comparison of the rainfall in May and the yield of hay in Ohio for the years from 1858 to 1909, gave a correlation of +0.49 with a probable error of ±0.07. The correlation for April and May was the next highest or +0.45, probable error =fc0.07. Fig. 71 gives a dot chart showing the relation between the rainfall in May and the yield of hay in Ohio. This indicates that a May rainfall of more than 1 inch above the normal, is always followed by a yield of hay above the normal. When the rainfall has been more than 1 inch below the normal, the yield has been below the normal eleven times and above five times. It is plain, therefore, that other influences besides the May rain affect the yield, especially when the rainfall is light, as a large yield is frequently harvested following a comparatively dry May. 505. Hay in New York. — A recent study covering twenty- three years, from 1888 to 1911, showed that a normal rainfall is most favorable in New York. In nine years out of twenty- three when the rain was within 2 per cent of the normal, the yield was over 8 per cent above the average. That this crop does not appear to utilize much more than the normal amount of moisture is indicated by the fact that in seven years when the rainfall was 27 per cent above normal, the yield was only 5 per cent above the average. On the other hand, a slight deficiency resulted in a marked decline in the yield. In five years when the deficiency was marked, the yield was 32 per cent below the average. 506. Hay in Wisconsin. — The correlation between weather and the yield of hay in Wisconsin for twenty-seven years is indicated in the following: Table 50. — Correlation between Weather and Yield of Hay in Wisconsin Rainfall Temperature Month Correlation Probable Correlation Probable coefficient error coefficient error April +0.05 -0.24 ±0.12 May +0.38 ±0.11 -0.11 June +0.25 ±0.12 -0.58 ±0.09 WEATHER AND MISCELLANEOUS CROPS 239 507. Hay in other states. — The following shows the cor- relation of the rainfall for April and May with the yield of hay for different states: Table 51. — Correlation of Rainfall for April and May with Yield of Hay Rainfall April May State Years Correlation Probable Correlation Probable coefficient error coefficient error California 19 Iowa 26 Nebraska 40 New Mexico 24 New York 26 North Dakota. ... 24 Oklahoma 14 Tennessee 33 Washington 26 Wisconsin 25 508. June rain. — Charts of the relation between the June rain and the hay jdeld indicate that the later rain has consid- erable effect on the yield in North Dakota, but not in Wiscon- sin or any of the southern or western states given in the above table. In New Jersey and in more southern districts, it is probable that the April or even March weather may have a greater influence than that of later months. 509. Alfalfa requires more water than most crops, but the ability of the plant to send its roots to great depths makes it very drought-resistant and a valuable croj:) for semi-arid regions. It is found that alfalfa thrives best where the water- table is at a fairly uniform height. 510. Alfalfa and temperature. — Alfalfa is able to with- stand high temperatures when the air is drj^, but if accom- panied by humid air high temperatures are injurious. If a hard freeze occurs soon after the plants come up, especially when the soil is damp, a large proportion may be killed. Al- falfa is liable to be winter-killed with freezing and thawing of the ground without snov/-cover. An ice-sheet is very dam- aging. +0.12 =^0.13 -0.017 ±0.19 +0.16 ±0.13 +0.56 ±0.09 +0.10 ±0.11 +0.45 ±o.oa +0.07 ±0.13 +0.18 ±0.13 +0.44 +0.12 ±0.11 ±0.13 +0.003 +0.35 ±0.12 +0.85 ±0.05 +0.28 ±0.15 -0.18 ±0.11 +0.32 ±0.10 -0.58 ±0.08 +0.07 ±0.13 -0.02 ±0.13 +0.44 ±0.11 240 AGRICULTURAL METEOROLOGY 511. Alfalfa in Nevada. — Alfalfa develops the highest food values when there is a high percentage of sunshine and the days are moderately warm and the nights cool. Enough moisture is needed to keep the soil in good condition, but too much cloudy weather is detrimental to the growth of slender stalks and a large number of leaves. Hot days and warm nights with much moisture cause the plant to develop a woody stock and fewer leaves. Plenty of sunshine, moder- ately warm days and cool nights cause alfalfa to develop more chlorophyll, which gives the plant more nutriment. 512. Curing alfalfa. — As this plant cures slowly, a good crop is frequently greatly damaged in harvesting in the humid sections of the country where rains are frequent. The im- portance of cutting during good weather has led to the es- tablishment of an alfalfa fair weather warning service by the United States Weather Bureau. Forecasts of three or four days or more of fair weather are made and widely distributed in the principal alfalfa-growing districts during the harvest- ing season. 513. Alfalfa seed and frost. — Alfalfa seed ripens unevenly and the best plants, setting burrs heavily well down on the lower stems, will contain many green burrs, yellow burrs (turning ripe), and brown or ripe burrs at the same time. The yellow stage of the burr endures for about one week in Utah under ordinary conditions during which time the seed, if cut, will ripen from sustenance in the parent stem, if in good con- dition. The seed-growers estimate that near harvest time the crop increases in value about $5 an acre each twenty-four hours. For this reason it is desired that the crop be allowed to stand as long as unripe seeds remain. A light frost or a temperature of 31° or 32° in the alfalfa foliage is harmless to the brown burrs, but will injure the exposed yellow burrs and some of the green burrs. A temperature of 26° to 28° in the foliage will cause heavy damage to both yellow and green heads, the injury varying with the amount of leaf foliage and the proportion of these immature burrs. The effect of the frost is to blacken the seed, making it less salable and prob- ably less viable. 514. Alfalfa seed warning service, Utah. — When the frost warning service is in operation, the seed is left standing until a warning is received. On receipt of the warning, as WEATHER AND MISCELLANEOUS CROPS 241 many mowers as are available are sent into the field and cut- ting is sometimes continued on moonlight nights well into the night. When cut, whether left flat or raked into windrows, comparatively little of the seed will be damaged. Tens of thousands of dollars worth of seed will be saved in this way on receipt of a frost warning. 515. Clover thrives best in a humid climate, and where the winter and summer temperatures are not extreme. It is said that white clover will withstand greater temperature ex- tremes than either red or alsike. Crimson clover is less re- sistant to low temperatures than the other common clovers. Sweet clover thrives best in rather humid regions, but also grows well in semi-arid districts. This crop is adapted to a wide range in temperature. 516. Weather and clover. — A correlation between the weather and yield of clover in Ohio covering a period of twelve years gave the following: Table 52. — Correlation between Weather and Yield of Clover IN Ohio District Franklin Co. Ohio Ohio Ohio Franklin Co. Ohio Franklin Co. Ohio Franklin Co, Period Winter Jan, March <( April May May Rain Correlation Probable coefficient error +0.50 +0.12 +0.38 ±0.14 =0.16 Temperature Correlation Probable coefficient -0.43 -0.32 -0.38 +0.75 +0.14 -0.51 -0.28 -0.41 error to. 15 to. 17 to. 16 to. 08 to. 14 517. Clover in Ohio. — A more extensive study of weather and clover yield in Ohio for the period from 1864 to 1913 gave correlations as follows: 242 AGRICULTURAL METEOROLOGY Table 53. — Correlation between Weather and Yield of Clover IN Ohio, 1864-1913 Rainfall Period Correlation Probable coefficient error April +0.15 =^=0.09 May +0.32 ±0.09 June -0.09 July +0.08 It is probable that the weather during the winter has a greater effect on the yield of clover than the rainfall of the spring or summer. 518. Clover seed. — Dry weather is unfavorable for clover, but favorable for the seed crop because fertilization by bees can go on better. The pollen grains of red clover are partic- ularly sensitive to moisture, hence there is little effective pol- lination when the flowers are wet. The time between pollina- tion and fertilization varies with the temperature. In July it is about eighteen hours and in October, thirty-five to fifty hours. 519. Timothy thrives best in a moist cool climate. It is unable to endure hot and dry summer weather and is not grown south of latitude 36° except at high elevations. The greatest number of flowers bloom in the early morning hours, from about midnight until the time of or soon after sunrise. The number of flowers that bloom each day, and also to some extent the time of blooming, are affected by weather condi- tions, especially temperature. Clear weather and a minimum temperature of about 60° or above are most favorable. Tim- othy flowers have not been observed blooming when the tem- perature during the preceding twenty-four hours was as low as 50° F. 520. Millet needs a fairly large amount of rain and must have warm weather during the growing season. It was found in Russia that between the formation of the leaves and the appearance of the flowers, temperature is the most important factor and should not fall below 18° C. (64.4° F.). Severe cold delays the appearance of the blossoms. The period be- tween the flowering and the ripening of the grain was most critical for rainfall. Millet has a comparatively shallow root system and therefore can well use light rains. WEATHER AND MISCELLANEOUS CROPS 243 521. Sorgo has a much deeper root system than millet and can use water from a lower depth. This crop can cease to grow during a dry spell and when a good rain comes will revive and make a rapid growth. Both crops have a very low water requirement and mature quickly. 522. Cowpeas are adapted to those sections with warm summers. 523. Rape grows best under cool and moist conditions. SUGAR PRODUCTS In the United States, sugar is produced from sugar-cane and sugar-beets, and to a limited extent, from maple sap. Large quantities of sirup are made from maple sap in the northeastern states and from sweet sorghums in the central and southern states. 524. Sugar-cane is a tropical plant and requires high temperatures and a large and constant supply of moisture for its best development. The length of time from planting to tasseling (the end of growth) varies in Hawaii from eighteen months to two and one-half years. The plant is damaged by cold weather, hence in Louisiana cane must be harvested in an immature state, with the result that the yield of cane aver- ages much less than in Hawaii. 525. Water requirements of sugar-cane. — The optimum rainfall for a crop in Louisiana is about 60 inches. Li the West Indies the rainfall of July and August and September decides the crop of the next year, whenever the canes are in a healthy condition at the end of June. In the Barbadoes it is stated that each inch of rain corresponds to about 800 hogs- heads in the resulting crop, or Vqo of a hogshead of sugar to the acre. In Mauritius, it is said that the number of marriages de- pends on the rainfall because of its effect on the sugar crop. Sugar-cane should have comparatively dry weather during ripening and harvesting and dry weather facilitates grinding. 526. Temperature effects on sugar-cane. — The rate of growth of cane increases with the temperature. Freezing weather kills the buds, hence the seed cane must be cut and windrowed in Louisiana before the temperature falls much below freezing. As the cane is cut in an immature state in 244 AGRICULTURAL METEOROLOGY Louisiana, the longer it can continue growing the higher the sugar-content; hence growers formerly suffered much loss from fall freezes. With the present excellent warning serv- ice, the cane is allowed to stand until a forecast of probable minimum temperature of 26° to 27° is issued by the Weather Bureau. A large force of men is then put into the fields and all the seed cane is windrowed and as much of the other cane as practicable. After the cane is frozen, windrowing is con- tinued as long as it remains frozen or until only an amount sufficient for two weeks' grinding is left standing. The sirup in this standing cane which has been frozen will not spoil, un- less it is too warm, for about two weeks, and grinding may be continued. The frozen cane that is windrowed and thaws out slowly receives no material damage. Sometimes a warn- ing of damaging temperatures will result in windrowing of cane valued at $10,000,000 to $15,000,000. 527. Sugar-cane in the United States. — Sugar-cane can be raised in all of the Gulf states, but it is not grown commer- cially for sugar in any quantity outside the lower Mississippi Delta in Louisiana. 528. Sugar-beets. — The growing of beets for sugar is a comparatively recent practice, particularly in this country. The first factory in the United States was at Philadelphia in 1830. In 1880 there were four factories in operation, but in 1890 only two. In 1900 this number had increased to only thirty with an output of granulated sugar worth only a little over $5,500,000. By 1909 the number of factories in opera- tion was about twice that in 1900, while the granulated sugar output was increased nearly ten times. Sugar-beet factories have been built in regions where sugar- beets produce well, and later have had to discontinue opera- tions because the sugar-content was found to be too low to make manufacturing financially successful. 529. Sugar-content of beets affected by temperature. — While the temperature and rainfall must be high enough for growth, it is found that moderate temperature and long hours of daylight are necessary to produce a high sugar-content. It must be cool during the ripening period especially, and there should be large diurnal variations in temperature. It is found that the successful beet districts are in regions where the mean temperature during the growing months is WEATHER AND MISCELLANEOUS CROPS 245 246 AGRICULTURAL METEOROLOGY not far from 70°. Fig. 72 shows the summer isotherm of 70"^ while a region on each side about 100 miles in width fairly well outlines the region of most of the sugar factories at the present time. 530. Sugar-beets as a winter crop. — Sugar-beets are suc- cessfully raised in southern California and parts of Arizona and New Mexico by making part of the growth in the winter months. The best fields in Colorado and Utah are at eleva- tions between 4000 and 5000 feet. A great amount of heat is not necessary when the plants are growing, neither will they thrive if the weather is cold and damp just after planting. Sugar-beets are very sensitive to frost when young, although they can stand rather cold weather in the fall. A hard freeze just as the plants are coming up is almost fatal. The crop should have about five months without severe freezing weather. 531. Effects of rainfall on sugar-beets. — Heavy rains in the spring delay planting. Drought retards growth so that a uniform rainfall or supply of irrigation water is needed dur- ing the growing period. From a five-year experiment in Utah, it was found that when watered each week, 1 inch weekly gave a higher yield than any other quantity. It was determined in Indiana that the rainfall should be not less than 2 inches or over 4 inches a month. Experiments have shown that a heavy rainfall is followed for several days by a reduced sugar- content. It should be rather dry during ripening as heavy rains may cause continued growth and a lessening of the sugar values. 532. Temperature for sugar-beets. — The limiting factors in successful beet-sugar production are too warm weather in the summer and too cold weather in winter for winter pro- duction. The difference between day and night temperatures should be large while ripening. The sugar-content will in- crease as the temperature decreases. In regions near the southern limit of the best production, a cool summer and fall produces the best results. 533. Sunshine for sugar-beets. — Sugar is made by the action of light on the green leaves when moisture and car- bonic acid gas are present. Actual sunshine is not so impor- tant as long hours of daylight, hence the sugar-content in- creases with increases in latitude. WEATHER AND MISCELLANEOUS CROPS 247 534. Correlation studies of sugar-beets. — The correlation coefficient between the average temperature for June, July, and August and the sugar-content of beets raised in 1901 to 1904 at five different places in the eastern part of the United States was —0.53 with a probable error of =t=0.11. The corre- lation coefficient between the June average temperature and the tonnage in the United States was —0.67, probable error =t0.10. Curves showing the relation between the mean tem- perature for either June, July, or August, or these months combined, and the sugar yield in different states and the Uni- ted States, gave in practically all cases a decreased 3'ield with an increased temperature. 535. Weather and maple products. — A study of the effect of weather on the yield of maple products covering thirteen years in Portage County, Ohio, showed that February should be warm and that March must be cool for the best results. The curves for the March mean or maximum temperature and the yield have an opposite tendency. The correlation coefficient between the mean temperature for March and the yield was —0.69, probable error ±0.08. Out of the six years when March was cooler than the normal, the yield was above the average every year but one. That year the mean was only slightly above normal while the yield was only 0.1 pound a tree less than the average. There is a chance for a very profitable study in this connection. 536. Weather and honey. — There is opportunity also for a very interesting and valuable study of the relation between the weather and the yield of honey. Such studies in Iowa covering the period from 1885 to 1914 showed that an abun- dant but not excessive rainfall in Maj^ is desirable. June, which is the honey month, should be drier than normal for best yields. A rainy period is generally a time of decreased production. Clear days before a rain show a slightly greater increase than the days immediately following. 537. Temperature and honey. — A cold March is unfavor- able for a good honey year. A record of the total yields of honey at different maximum temperatures for all single days recorded in 1885 to 1914, showed the following: 248 AGRICULTURAL METEOROLOGY Maximum Percentage of temperatures honey -production Less than 70° 1 per cent 70 to 800 ' 8 " " 80 to 900 53 " " 90 to 100 37 " " Over 100 1 " " Considering all days for the months of June, July and August. Temperatures All days less than 80° " " 80 to 90 " " over 90 Percentage of total honey produced 17.3 45.4 37.3 TOBACCO Tobacco was used by the natives in North, Central, and South America when first visited by Europeans. There are three general classes of tobacco grown in this country, each of which is best developed under specific climatic and soil con- ditions. 538. In the United States. — The two most extensive dis- tricts of tobacco-culture in the United States are in northern and western Kentucky, including northwestern Tennessee, and southwestern Ohio, and in northern and eastern North Carolina and southern and central Virginia. Smaller though intensive areas are in southern Wisconsin, south-central Maryland, southeastern Pennsylvania, and north-central Connecticut, while a considerable amount is raised in north- eastern South Carolina. 539. Climate and tobacco. — The distribution of the crop shows that it is extensively grown under quite wide variations of temperature and rainfall. The tobacco plants are very susceptible to frost; hence, the seed is planted in beds and the plants are set in the fields after all danger from frost is over. The beginning of transplanting varies from the latter part of March in northern Florida to the first part of June in Wis- consin and New York. The crop is generally ready to cut and house about three months after it is transplanted; hence, WEATHER AND MISCELLANEOUS CROPS 249 there is occasionally damage from fall frosts in the northern states. 540. Under shade. — Considerable tobacco is grown under cloth shade, particularly in the Connecticut Valley. The ef- fect of the covering is to conserve the moisture of the soil, increase the temperature and relative humidity of the air, and reduce the wind velocity. 541. Weather and tobacco. — Tobacco is a weed and grows most rapidly with plenty of moisture and warm weather. In the shade experiments, it was found that the rate of growth increases with higher temperature and de- creases with lower. If there is a decided drop in temperature, there is a decrease in the growth which continues for a day or two after the temperature has begun to rise. If the plants get a good start after transplanting, they will stand practi- cally dormant during a drought and will then grow rapidly when rain comes. 542. In Kentucky. — A study of the weather and yield of tobacco in Kentucky covering a period of twenty years showed that June should be warm and wet to produce the best yields, although there were some marked exceptions to that rule. Neither the mean temperature nor the total rainfall for July was a determining factor in varying the yield. Rain- fall in August was favorable, while the best yields followed a rather dry and cool May. 543. In Ohio. — A comparison of the yield of tobacco in Ohio with the temperature and rainfall departures from the normal for the state as a whole from 1881 to 1907 shows little relation, probably from the fact that tobacco is grown only in parts of the southern and western portions of the state. 544. Darke County, Ohio. — This is the most important tobacco-growing county in Ohio. Two independent studies have been made in this county covering the period from 1886 to 1909. Both investigators found that a wet August was desirable and that the months of June and July combined should be slightly cooler than the normal. No relation was observed between the yield and either the mean maximum or mean minimum temperatures, or the number of rainy days. 545. Montgomery County, Ohio, 1883 to 1908.— June should be warm, as a cool and dry month is decidedly unfavor- able to the yield. Hot weather kills the cutworm. Too much 250 AGRICULTURAL METEOROLOGY rain in this month will force the plants into top. July should be cooler than normal, as the average temperature is a little too high unless the rainfall is above normal. If the rainfall is much above the average, it ijiterferes too much with culti- vation. August should be cool if it is dry, as hot and dry weather is decidedly unfavorable. Warm and wet weather is most favorable for growth, but is likely io develop rust. 546. Southwestern Ohio. — This study covered the coun- ties of Darke, Miami, Preble, Montgomery, Warreil, and Butler, from 1863 to 1913, inclusive. The following correla- tion table does not include 1875. That year the rainfall for June, July, and August totaled 22.7 inches or 7.8 inches above the normal, while the yield of tobacco was 470 pounds below, showing conclusively that the rainfall was too great for best yield. Table 54. — Correlation Between Weather and Yield of Tobacco IN Southwestern Ohio, 1863 to 1913 Rainfall Temyerature Period Correlation Probable Correlation Probable coefficient error coefficient error July +0.21 ±0.09 +0.03 ±0.10 August +0.56 ±0.06 -0.30 ±0.09 July and August... +0.43 ±0.08 -0.21 ±0.09 While this table shows that August is evidently the most critical month, possibly some other period could be found which has a more direct control on the yield. The student states that '^A study of the original data indicates that the highest yield of tobacco is produced when the combined rain- fall for July and August is about 3 to 4 inches above the nor- mal. A greater excess is usually quite detrimental to a high yield. When the rainfall for August is about normal it seems that the July rainfall is the large controlling factor." 547. Summary. — The conclusions drawn from the above are that May should be moderately dry for a good seed-bed, and cool to harden the tobacco plants. June should be mod- erately warm and wet to insure growth when the plants are set out, unless the warm and wot weather develops bed-rot; July rainfall and temperature not far from normal, as too WEATHER AND MISCELLANEOUS CROPS 251 much rain interferes with cultivation; if dry, the temperature should be below the normal. August should have rain enough to produce a good sized leaf after topping. Warm and wet weather makes the best growth but is more likely to cause the development of rust. Hot and dry weather is very detri- mental; hence if the rainfall is less than normal the month should be cool. If the growing season is moderately wet with a uniform supply of moisture, the best growth will be with the temperature somewhat above normal. But if drought prevails or frequently occurs, the best results are obtained with the summer somewhat cooler than normal. 548. Tobacco root-rot. — While this disease is influenced by moisture and condition of the soil, the soil temperature is the most important factor affecting its extent. The most favorable soil temperatures for the development of the dis- ease range from 62° to 74°. Below 59° the disease is less marked, while above 90° practically no infection occurs. June is the most favorable month for the development of to- bacco root-rot, from a temperature standpoint. A heavy in- fection in June may be overcome by a very warm July. SEEDS 549. Effect of weather on maturing seed. — It has been found in England by Hooker that the weather during the maturing of peas and beans has a very great effect on the yield of the crop from this seed. The ripening period must be dry. The lack of rainfall at harvesting time, making it b}^ no means rare to gather and thrash a crop of seeds without its having been touched by a drop of water, is one of the reasons why beans and peas and short-season seeds raised in Idaho and other semi-arid states are in such demand. 550. Seeds from drier regions. — It is commonly better to use seed grown in a region of smaller rainfall during matur- ing, particularly in a comparatively dry district. Also in- stead of using seed that matured during wet weather, it is better to discard that and obtain seed from a drier region or even to use seed one year older if that was grown under the more favorable conditions of less rainfall and more sunshine. 551. Alfalfa seed. — The alfalfa crop that is saved for seed should have warm wet weather or ample storage mois- ture at the beginning of its growth, followed by fair and not 252 AGRICULTURAL METEOROLOGY too hot weather during blooming. A mean monthly temper- ature somewhere in the middle seventies is evidently favor- able for the plant at the critical period of blooming. The season of growth and harvesting of seed must be quite free of frost. 552. Potato seed. — Immature potatoes or at least those not over-ripe are best for seed. Northern-grown potato seed is preferred not only because it may be less ripe when har- vested, but is stored where it is kept dormant and solid. A temperature of 32° to 40° is best in storage in order to main- tain the dormancy of the tubers. 553. Wheat seed. — Spring wheat seed obtained from farther north will ripen earlier and give a better yield and quality than seed from the same strain ripened farther south. Winter wheat seed, on the other hand, from points farther south will give better yields than northern-grown seed of the same variety. 554. Regions especially favorable for seed. — There are well-recognized localities especially favorable to the produc- tion of seeds of high quality. For example, alfalfa seed will mature well only in the dry climate of the semi-arid West. Some of the common opinions about these matters have not been wholly verified, but they are so general and are so evidently a climatic matter that they are worth mentioning. Onions grown from California seed are different in keeping quality from those from Michigan seed; cabbage, cauliflower, and the like, head better from seed grown on Long Island or in the Puget Sound region than from any other section; to- mato plants raised from seed produced in northern states are far superior to those from seed in the South. 555. Good " seed " weather. — It is probable that po- tatoes and turnips yield best when ripened in cool weather; that most of the cereals, clover, and most grain seeds are better ripened under warm conditions, while beans, peas, and some other legumes should be ripened under dry conditions. PLANT DISEASES AND INSECT DAMAGE There is a close relation between the weather and the dam- age done by plant disease and by insects. In many of these the kind of weather that favors the most rapid development of the disease or of the damaging insects is well known; in WEATHER AND MISCELLANEOUS CROPS 253 others it remains to be worked out, thus making it important that all farmers keep a careful record of the weather factors when disease or insect damage is prevalent and when this damage is checked. 556. Terms relative. — In the designation of ''dry" or "wet" weather diseases and "warm" or "cold" weather dis- eases, it must be remembered that the writer is speaking in relative terms as compared with the average condition at the place of record. Plant diseases are not abundant in the trop- ics and yet various wilt and root diseases and many leaf troubles spread in Louisiana during the hottest weather there. On the other hand, many diseases common in the North are troublesome in Louisiana only in " cool " weather. The onion mildew and the bean anthracnose are well-marked examples. 557. Bitter-rot of apples is a common and destructive disease in the South but it is a botanical curiosity in New Eng- land. Apple-scab, on the other hand, is more prevalent in northern districts. Pear-blight is also a disease common only in warmer regions. 558. Late blight of potatoes. — In extreme northern dis- tricts this is spoken of as a "warm" moist weather disease, while in slightly more southern states it is known as a "cool" moist weather disease. It develops with greatest rapidity in moist weather, but the optimum temperature for its most rapid development is at about 72'^. Contrasted with the potato Phytopthora is the allied dis- ease, cucurbits, the downy-mildew, which appears to flourish during hot seasons and to disappear in cool ones. In Wiscon- sin the summer of 1915 was cool and moist and the late blight caused immense damage to potatoes, but the cabbage crop was everywhere vigorous. In 1916 it was hot and dry and while there was practically no potato late bhght, cabbages were "swept as if by fire" by the yellow disease Fusarium conglutmans. 559. Wet weather diseases. — It is agreed by all plant pathologists that the presence of water is necessary for the spread of bacterial diseases. All fungi are also favored by a large amount of moisture while some develop most rapidly under conditions cooler than normal and others are favored by temperatures higher than normal. An example of the last named condition is the "scab" or "black-spot" of cucumbers 254 AGRICULTURAL METEOROLOGY which sometimes causes much damage in the pickle-growing regions of Michigan, Indiana, and Wisconsin. 560. Dry weather diseases. — Some of the most well- defined dry weather diseases are the point-rot of tomatoes, the cabbage black-rot and the southern bacterial wilt of po- tatoes known as the '' sleeping sickness." 561. Grain rusts. — Hot and humid weather at the ripen- ing period favors a rapid development of rust and these con- ditions in many years limit the southern development of successful wheat-growing. In the spring wheat region of the Northwest, stem-rust often does great damage; in 1904 it was estimated that the loss from rust in North Dakota, South Da- kota, and Minnesota amounted to $10,000,000. The con- ditions favorable for rust in that region are muggy, sultry, rather still, hot days with foggy cool nights at about the blos- soming period. Just after the infection, cool, moist, slow- growing, showery weather may result in widespread damage. 562. Spread by the wind. — Bacteria being present in the leaf surface water film, are splashed up by the impact of fall- ing raindrops, and these bacteria-laden drops are carried by the wind to a distance proportional to its velocity. The dis- tance of the splash varies according to the size of the drop, depth of surface film, elevation and inclination of the surface of impact, and the velocity of the wind. Faulwetter found that with a wind of ten miles an hour a drop of rain 0.02 cc. in volume falling 16 feet the splash was carried in abundance 8 feet, in moderate quantities 12 feet, and in slight amount 16 feet, while a wind of thirty miles an hour carried the splash at least 50 feet. 563. Smuts. — It has been found that the soil tempera- ture at the time of germination is an important factor in the development of the stinking-smut of wheat. The most favor- able temperature is between 59° and 72° while a soil temper- ature above 72° or below 41° is decidedly unfavorable for the development of the disease. For this reason, winter wheat sown very early in warm soil or very late in cold, in the Pacific Northwest, is comparatively free from the disease. It has been found that the soil temperature is an important factor in the development of the Fusarium wilt of potatoes, as well as another Fusarium disease the '^ flax-wilt." In some exper- iments the flax developed normally when the soil temperature WEATHER AND MISCELLANEOUS CROPS 255 was held continuously below 59°, but if the temperature rose above 61° even for one day, infection occurred and wilt de- veloped. 564. Insect damage. — It is well recognized that the ac- tivity of insects is affected by weather conditions, and that they cause more damage some seasons than others because of the characteristics of the weather. 565. Grasshoppers. — It is generally experienced in the middle and western states that when two dry summers occur in succession, the second one usually has a serious outbreak of grasshoppers. Dry weather favors the hatching of the eggs while in cool wet weather the grasshoppers often die in large numbers from disease. 566. Chinch-bugs. — Warm dry weather is favorable for an increase in chinch-bugs. A succession of dry summers, especially in May and the first part of June, and in August and the first of September, thus covering the two hatching periods, is very likely to cause an outbreak in a region subject to infection. The damage by chinch-bugs in thirt^^-eight counties in Illinois in 1914 was estimated at $6,400,000. The year was very dry, particularly in June, and there was a marked absence of heavy beating rains from May to August. This year was one of a series of rather dry summers in the region of infestation from 1910 to 1914. The next year the late spring and summer were cooler than normal and there was an abundance of heavy rain-storms which put an end to the destructive outbreak in one season. 567. Temperature and chinch-bug. — It was found in Illinois that the chinch-bug does not ordinarily begin its movements until the temperature reaches 74°, while on hot bright days its activities cease from 10 or 11 o'clock until 3 or 4 p. m. It was observed that they make little or no move- ment after twilight. 568. Effect of wind on insects. — The chinch-bug tends to move with the wind especially when on the wing. Warm days, with strong winds after rain or dull days, showed a rapid advance to the leeward. In New England it was found that the gipsy moth made a general progress of five miles a year toward the northeast, the direction of the prevailing winds, while the spread was only three miles a year toward the west. 569. Cutworms. — A study in Marion County, Ohio, 256 AGRICULTURAL METEOROLOGY showed that the weather during May exerted a strong influ- ence on the damage done by cutworms. It was found that a cool and wet May was favorable to cutworm activity, while a warm and dry May was unfavorable. The correlation coef- ficient between temperature in May and the percentage of damage to corn in the county was —0.50, probable error =±=0.11. It was +0.34, probable error =b0.14, between rain- fall and damage. 570. White-grub. — It was found that the correlation co- efficient between the temperature in May and the percentage of damage by the white-grub was —0.55, probable error =1=0.11, and between rainfall and damage +0.51 and probable error d= 0.11, showing that a cool and wet May was also favor- able to the activities of this pest. 571. Hessian fly. — Augestine found that the highest cor- relation between weather and damage by the hessian fly was with a warm October and a dr^^ April. The correlation co- efficient between the October temperature and damage was +0.62, probable error, ±0.10, and between April rainfall and damage, —0.72, probable error =t0.08. 572. Insect pests and parasites. — The effect of the weather on parasites or fungous diseases of insects may be different from that on the insects themselves. For example, the oat aphis breeds and multiples at a temperature of about 40° or above, while the common parasite of this and many other aphids is not active at a temperature below 56°. Con- sequently, a mild winter and cool spring, when the tempera- ture fluctuates between 40° and 56°, permits the aphis to multiply unchecked by the attacks of the common natural enemy. At a temperature of about 70°, however, the para- site will multiply about ten times as rapidly as its host, hence at that time the plant-lice are soon destroyed by the parasite. 573. Cattle-tick. — A study by Cotton and Voorhees showed that zero weather is fatal to the cattle-tick in all stages, unless the tick is on an animal or in a well-protected building. Adults were killed at a temperature of 14°, the seed ticks at 4°, and eggs at 2°, when exposed under condi- tions similar to grass in ordinary pastures. They found that the ticks will not permanently occupy a territory where zero temperatures occur, or where the mean relative humidity is below about 60 per cent. WEATHER AND MISCELLANEOUS CROPS 257 LABORATORY EXERCISES (1) A study of the effect of the weather during the ripening of seed on its viability and vigor is of much importance. Whenever germination records are available covering any considerable number of years, corre- lations may be made with the weather condition. (2) Another problem that needs more study is the influence of differ- ent soil temperatures on germination; Time necessary and percentage of germination. REFERENCES Vegetables California Agricultural Experiment Station Bulletin 294. Colorado Experiment Station Bulletin 209. Cornell University Reading Course, No. 112, Vol. V, 1918. Effect of Weather on the Yield of Potatoes. J. Warren Smith, Monthly Weather Review, May, 1915. Home Gardening in the South, Farmers' Bulletin 934. Investigations of the Potato Fungus Phytopthora Infestans. L. R. Jones and others, Bureau of Plant Industry Bulletin No. 245. New York State College of Agriculture, Reading Courses, Lesson No. 124. Oregon Experiment Station Bulletin No. 122. On the Occurrence of Phytopthora Infestans and other diseases. A. D. Selby, Ohio Naturalist, February, 1907. U. S. Department of Agriculture Bulletin, 561. Utah Experiment Station Bulletin No. 157. Potato Culture. Chas. D. Wood, New Jersey State Board of Agricul- ture, 36th Annual Report, 1909. MISCELLANEOUS Alfalfa Seed Growing and the Weather. J. Cecil Alter. Utah Agri- cultural College Experiment Station, Bulletin No. 171, 1920. A New Interpretation of the Relationship of Temperature and Humid- ity and Insect Development. W. D. Pierce, Journal of Agricultural Research, March 20, 1916. Beet-Sugar Industry in the United States, U. S. Department of Agri- culture Bulletin No. 721. Illinois Experiment Station Circular 189. Influence of Environment on the Chemical Composition of Plants. H. W. Wiley, Yearbook, 1901. Iowa Experiment Station Bulletin No. 169. Irrigation of Sugar-Beets, Farmers' Bulletin No. 392. Journal of American Society of Agronomy, Vol. 8, No. 5, pages 299-309. North Dakota Experiment Station Bulletin 68. Ohio Agricultural Experiment Station Circular 115. 258 AGRICULTURAL METEOROLOGY Phylopathology. L. R. Jones, The Plant World, August, 1917. Sugar-beet in America, The. F. S. Harris, The Macmillan Co., 1919. Sugar-beets in Indiana, Indiana Experiment Station Bulletin No. 68, Vol. IX. Strains of White Burley Tobacco Resistant to Root-rot, U. S. Depart- ment of Agriculture Bulletin, No. 765. Tennessee Agricultural Experiment Station Bulletin No. 94. The Hessian Fly and how to Prevent Losses from it. W. R. Walton. Farmers' Bulletin 1083, March, 1920. Tobacco. G. N. Coffee, Monthly Weather Review, 1907, page 346. ^ Tropical Agriculture. E. V. Wilcox, D. Appleton & Co., 1916. Utah Experiment Station Bulletin No. 156. Wind-blown Rain, a Factor in Disease Dissemination. R. C. Faul- wetter, Journal of Agricultural Research, September 17, 1917. CHAPTER X WEATHER FORECASTS AND WARNINGS The United States Weather Bureau issues regular forecasts of the weather twice each day, while special forecasts and warnings are put out whenever the conditions warrant. 574. Forecast centers. — District centers, at which fore- casts are made for a district covering several states, are lo- cated at the Central Office in Washington, D. C, and at Chi- cago, Illinois, Denver, Colorado, New Orleans, Louisiana, and San Francisco, California. 575. A. M. forecasts. — The morning forecasts are made at about 9. a. m., eastern time, and cover the probable condi- tions thirty-six hours in advance. These forecasts are imme- diately telegraphed from the centers to about 1600 principal distributing points, whence they are further disseminated by telegraph, telephone, wireless, and mail. These are the fore- casts that appear in the afternoon papers. These forecasts reach nearly 100,000 addresses by mail, and are available to more than 5,500,000 telephone sub- scribers within an hour after the time of issue. Many thou- sands of persons never think of starting on a trip, or of taking up any important work that is affected by the weather with- out calling up the Weather Bureau Office or the nearest tele- phone exchange and asking for the official forecast for the next thirty-six hours. 576. Value of forecasts. — Shippers of perishable products must know the forecasts. Commission-men and other ship- pers of perishable products in most of the important cities always delay their morning shipments until they know from the forecasts what temperature to expect and how to prepare their goods for it during transit. The railway and transpor- tation companies make continuous use of the forecasts in all their shipments. Often shipments of perishable goods are accelerated or protected against temperature extremes by icing or heating, as conditions may require. Bananas, for ex- 259 260 AGRICULTURAL METEOROLOGY ample, must be kept at a temperature of 58° to 65° during shipment, as a temperature below 55° chills the fruit suffi- ciently to cause a deterioration in quality, while a tempera- ture above 65° inside the car will produce over-ripening. The shipment of live-stock by freight is avoided, if possible, when a hot wave is expected. High temperatures are hurtful to certain other shipments, such as fish and oysters, so that the question of the proper amount of ice to be used is intimately connected with the forecasts issued. 577. Special forecasts for agricultural interests. — Some of the special forecasts issued for and widely used by the agri- cultural interests are the following: Alfalfa cutting. — Throughout the principal alfalfa-growing districts, special three or four day fair weather forecasts are issued at harvesting time. Sheej) shearing and lamhing. — Special forecasts of snow or rain, especially with wind and low temperature, are widely distributed in the West at shearing and lambing time so that shearing may be delayed or if done sheep may be protected, and extra precautions taken to care for young lambs. Spraying forecasts. — It has recently been necessary to have spraying experts in important apple and other fruit-growing districts and even to detail special weather forecasters to these regions so that spraying may be done before rainy pe- riods to prevent the rapid dissemination of apple-scab and other diseases. Raisin-drying. — In the raisin-growing districts of Califor- nia, rain forecasts are of great value. The raisin crop while drying is extremely susceptible to injury from rains, and the forecasts enable the growers to stack and protect the drying trays. Rain forecasts are also utilized in the large fruit-grow- ing districts to hasten picking before a rain, so that the fruit can be shipped while dry. 578. P. M. forecasts. — The evening forecasts are made at about 9 p. m. eastern time, and cover the two following days. These forecasts are sent throughout each district by the Press Association wire service. These appear in the morning newspapers. 579. Local forecasts. — The weather forecasts at district centers are for states or sections of states. At most of the other Weather Bureau Offices, the official in charge amplifies WEATH'ER FORECASTS AND WARNINGS 261 or modifies these state forecasts to cover the probable condi- tion in the particular city or vicinity where each office is lo- cated. These forecasts are based on a knowledge of the weather that is prevailing throughout the country and certain well-de- fined laws of the weather, 580. Observations. — A record of the pressure, tempera- ture, weather, wind, clouds, humidity, amount of rainfall, and extremes of temperature during the preceding twelve hours, and the like, is made by trained observers at about 200 different points at 8 a. m. and p. m , eastern time. Within five minutes after these observations are made, a telegraphed message in code, giving all the essential weather facts, is filed at the local telegraph office and by an ingenious *' circuit" system is placed in the hands of the Weather Bu- reau officials at Washingtion and at about 180 other stations in the country, within thirty minutes after the instruments are read. 581. Weather maps. — As fast as the telegrams reach the various offices, the data are charted by trained men on out- line maps of the United States, so that by the time the last report is received the forecaster has a complete weather map before him. When these maps are completed, each forecaster has before him an actual picture of the weather that prevailed through- out the country half an hour previously. He can see the pressure and temperature of the air, not only at his station, but at every other station. He knows where it is raining or snowing; the amount of precipitation that has fallen at each place during the preceding twelve hours, the wind direction and velocity, the kind, amount, and direction of move- ment of the clouds; where and when thunder-storms oc- curred and any other fact that is of importance regarding weather. Used in connection with a similar map of twelve, twenty-four, thirty-six, and forty-eight hours before, he can trace the movement of the various weather conditions from place to place. 582. Weather laws. — A study of the daily weather maps shows that the wind does not "blow where it listeth," but that there are well-defined laws that regulate the wind and the movement of storms and general weather conditions. 262 AGRICULTURAL METEOROLOGY 583. 1st law: weather moves eastward in temperate latitudes. — In the temperate latitudes in both the southern and northern hemispheres, the weather conditions move in a general easterly direction with a fair regularity of motion. This is the most important law of storms. The atmosphere near the surface of the earth moves in wave-like areas of high and low pressure. Fig. 73 shows the average paths over Fig. 73. — Average tracks of high and low pressure areas in the United States as they move from west to east. The broken lines running from northeast to southwest show the average distance traveled each twenty-four hours. which these areas move in the United States, as well as the average distance traveled each twenty-four hours. 584. 2nd law : the direction of surface winds depends on the difference in pressure. — On the weather maps (see Figs. 74 and 75), the solid Ikies are those of equal barometric pressure or isobars. The word ''high" indicates the centers of the high pressure areas and the word ''low" centers of low pressure. Arrows on the maps show the wind direction at the time the obser- vations were made. The arrows fly with the wind, and it will be seen that the wind blows toward the center of the lows, WEATHER FORECASTS AND WARNINGS 263 and away from the center of the highs. This is the second im- portant law of the weather. A wind from the east on the Atlantic Coast is usually fol- lowed by a rain because the wind is blowing toward a storm that is approaching from the west. These low-pressure areas or storms are usually accompanied by rainy weather and rain begins to fall when the center gets near enough. After the storm center passes by, the wind shifts to westerly, as it still Fig. 74. — 'A typical winter storm Dec. 15, 1893, that is central over southern Iowa. blows spirally toward the center, and fair weather usually follows. 585. 3rd law: the temperature at any place is largely controlled by the wind direction. — The dotted or broken lines on the weather maps are lines of equal temperature or isotherms. It will be seen that these temperature lines curve to the north in front or to the east of the lows, where the winds are from the south, and curve toward the south to the west, or in the rear of the lows where the winds are from the north. It is warm in front of the low pressure areas because the winds are coming from a warmer region. North winds bring cooler weather because they are coming from a cooler region. 264 AGRICULTURAL METEOROLOGY 586. 4th law: pressure areas and weather. — Low-pres- sure areas are usually accompanied by cloudy weather with rain or snow, while high-pressure areas are more likely to be attended by clear skies and fair-weather. As these areas move eastward, they carry along with them the weather, tempera- ture, and wind variations described above. 587. Weather forecasts are made for any particular region by estimating the path and rate of movement of a Fig. 75. — The same storm twenty-four hours later, Dec. 16, 1893. The temperature lines are shown on this chart. The arrows at each station show the wind direction; they fly with the wind. low or high pressure area west of it, the probable weather that it will cause, how it will affect the wind direction, and through the wind direction the temperature. 588. Special warnings. — In addition to the regular twice- daily weather forecasts, special warnings are issued for pecul- iar conditions and interests. Some of the most important are given below. Storm warnings. — Warnings of high winds and hurricanes influence the handling of the shipping all along the coasts. Flood warnings. — Forecasts of the height of the water in the large rivers can be made very accurately, days and some- WEATHER FORECASTS AND WARNINGS 265 times weeks in advance. Warnings of floods are made when- ever it is expected that heavy rains will cause a sharp and con- tinued rise in the streams. Some of the most fertile soil is in the river valleys and warnings of damaging waters are very valuable and can be obtained from the river district centers. Cold wave warnings. — These warnings are utilized by many interests and millions of dollars worth of damage averted by their receipt. Frost warnings are issued for truck-growers and orchardists in protecting crops from fros*-; damage. (See Chapter XL) Warnings for stockmen. — C Id wave, high wind, and heavy snow warnings are issued for the benefit of stock-growers over the Great Plains and in the West. Heavy snow warnings are issued for railroads and other transportation companies. LOCAL WEATHER SIGNS Certain local signs are valuable in anticipating the weather for a few hours in advance only. These relate largely to the relative humidity, clouds, and air pressure. 589. Humidity. — There is usually an increase in the humidity of the air before a rain because the latter is usually preceded by warm southerly winds that are taking up mois- ture as they flow northerly. Warm moist air attends a fall- ing pressure, and under these conditions there is a feeling of physical and mental lassitude that is in striking contrast to the feeling of exhilaration that accompanies the cool, dry, electrically-charged westerly winds that come with a rising barometer. The lower animals and insects, a,s well as humans, are undoubtedly affected by these cond'*:ions. 590. Good rain-indicators. — Certain phenomena are brought about by increasing moisture i^Ad hence are good rain-indicators. Some of these are : sweating walls, sidewalks, metal plates, and dishes; tightening of ropes; increase in per- fume of flowers; softening of moss; shortening of guitar strings; increase in odor from drains and ditches; tightening up of curls, and the like. The American Indians say: ''When the locks turn damp in the scalp house, surely it will rain." Floors saturated with oil become very damp, salt increases in weight, and tobacco becomes moist before a rain. 266 AGRICULTURAL METEOROLOGY Corn fodder is very sensitive to any increase of moisture in the atmosphere and becomes damp and Ump before a rain. It is said that before a rain the leaves of many trees are turned up or twisted over so as to show more of the under side, and if this is true it is probably caused by the absorption of mois- ture from the atmosphere by the wood fibers in the stem. 591. Moisture in vapor form. When the stars begin to huddle, The earth will soon become a puddle. ''When the sky is full of stars, expect rain." When there is an increased amount of moisture in the atmosphere in the form of vapor, there is usually a greater homogeneity of the atmosphere, hence its transmissibility for both light and sound waves is increased. For this reason when the amount of water-vapor increases, stars that are usually visible only with a telescope may be seen with the naked eye. Under sim- ilar conditions, sound is carried more readily and the singing of birds and the calls of domestic fowl are plainer and more noticeable. This is why ''parrots whistling indicates rain," and When the peacock loudly bawls, Soon we'll have both rain and squalls. 592. Pressure of the atmosphere.^ — The differences in air pressure are not great enough at any single point to be no- ticeable to man. It seems possible, however, that the differ- ence in the supporting power of the air between high pressure (usually fair weather) and low pressure (usually stormy weather) condition makes some difference in the flight of birds, and has thus led to "Everything is lovely and the goose hangs (honks) high," and the saying that swallows and mar- tins fly low just before a rain, and that bees remain in or near their hives just before stormy weather may be expected. It has often been noticed that water will begin running in ditches that are fed by springs just before a rain, although they have been quite dry. This is undoubtedly due to the fact that the decreased weight of the atmosphere in a low pressure area allows the ground water-level to rise slightly. 593. Wind and pressure. — When the wind sets in from points between south and southeast and the barometer falls steadily, a storm is approaching from the west or northwest, WEATHER FORECASTS AND WARNINGS 267 and its center will pass near or to the north of the observer within twelve to twenty-four hours, with winds shifting to the northwest by way of southwest and west. When the wind sets in from points between east and northeast, and the ba- rometer falls steadily, a storm is approaching from the south or southwest, and its center will pass near or to the south or east of the observer within twelve to twenty-four hours, with winds shifting to northwest by way of north. The rapidity of the storm's approach and its intensity will be indicated by the rate and the amount of the fall in the barometer. 694. Clouds. If clouds look like they had been scratched by a hen, Get ready to reef your topsails then. When ye see a cloud rise out of the west, straightway ye say "There cometh a shower"; and so it is. — Luke XII, 5-1. The clouds are the "storm signals of the sky," and by watching them carefully very accurate prognostications can be made for a few hours in advance. 595. High clouds. — The high cirrus and cirri-stratus clouds are particularly valuable in this respect, especially if they are of the thin wispy type sometimes called ''mare's tails." These clouds are composed of ice spicules and are formed by the condensation of moisture in high altitudes, that has been carried up in a storm area that perhaps is west of the observer and is moving toward him. 596. Hales, or large circles around the sun and moon, are formed by the refraction of light through these ice parti- cles and are frequently indicative of stormy weather. If the high clouds are moving rapidly eastward and the sky below is partly covered with denser clouds moving westward, then the storm is approaching rapidly and will probably cause heavy rain and strong wind. 597. Low clouds. — Lower clouds are so closely connected with the rainfall that they are generally of little value in in- dicating the weather for any considerable time in advance. When the lower clouds begin to break up and enough clear sky can be seen 'Ho patch a Dutchman's breeches," fair weather may be expected very soon. 598. Fog or mist. — "When Lookout Mountain has its 268 AGRICULTURAL METEOROLOGY cap on, it will rain in six hours." This is true in general with other mountains, but only "when the fog goes up the moun- tain you may go hunting, but when it comes down the moun- tain you may go fishing." LONG-RANGE FORECASTS Weather forecasts of a quite general nature are made for a week in advance by the Weather Bureau, by enlarging the observational field through daily reports by wireless and cable from different places in the northern heinisi^here. 599. Seasonal forecast not yet possible. — It is not pos- sible at the present time, however, to predict storms for a longer time than a week or ten days in advance, and the gen- eral weather of a month or season in advance cannot 3'et be determined. The officials of the Weather Bureau believe that the time will come when seasonal forecasts can be made, but it cannot be done at the present time with sufficient accuracy to warrant the attempt. Some of the most able scientific men of the century are at work on the problem, and sufficient has become known to be sure that it nnist be solved through a stud}' of the solar energy alone and its effect on the atmos- phere. 600. Planets have no known effect on the weather. — The planets have no effect whatever on the weather, and the effect of the moon is so slight as to be outside of consideration. No forecasts that pretend to predict the movements of storms for weeks in advance should be taken seriously, and all efforts to make predictions of the weather for months in advance, based on the movements of the planets, appear to be utterly unreliable. 601. Animals, birds, and plants. — In connection with the long-range forecasts, it may not be out of place to state also that animals, birds, and plants show by their condition the character of past weather and by their actions the influence of present weather, and possibly the character of weather changes that may occur within a few hours, but never the weather that may be expected during the coming winter or sunnner. Also that the weather of certain days, months, seasons, or years, affords no reliable indications of future weather, but show present abnormal conditions that the fu- ture may adjust. WEATHER FORECASTS AXD WARNINGS 2f39 LABOKATOKY EXERCISES 1. Paragraph 08 1. Practice should be given in making daily weather maps. The necessary data can he obtaincnl from the publishe^l tables or from the nearfist Weather Bureau Office, 2. Paragraph 582. A series of weather maps covering successive four to six day periods can be obtained from the Weather Bureau and from their use in the class the varioas "weather" laws can be demon- strated, and from them forecasts can be attempte<^l. The student will soon see that forecasting the weather is not so easy as it first seems and that there are marked exceptions to general rules. 3. Paragraphs o89 Uj 508. Forecasts should be regularly made from local weather .signs. This will .soon show that it cannot be done for any considerable time in advance. REFERENCES Weather Forecasting in the Unite^I States. U. S. Weather Bureau, 1916. CHAPTER XI FROST AND THE PROTECTION OF CROPS FROM FROST DAMAGE The limiting factor in the successful cultivation of many crops is the usual date of the last killing frost in spring and the first frost in autumn; and in themselves, frosts are likely Fig. 76. — Average dates of last killing frost in the spring. to set the bounds for much of the farm work. The relation of frost to crop-production may now be considered. 602. Average killing frost dates. — The average dates of the last killing frost in the spring and the first in the fall are shown respectively by Figs. 76 and 77 for the different sec- tions of the country. Frost may be expected one year in two, on an average, on the dates indicated, while the dates when frost may be expected only one year in ten will be about two weeks later in the spring and two weeks earlier in the fall. 270 FROST AND FROST DAMAGE 271 603. The growing season. — The potential growing season in any locality is usually considered to be the average number of days between the spring and fall killing frost dates. A map showing these days is given in Fig. 78. For tender crops that are killed by frost, the possible grow- ing season is less than indicated on the chart, because the killing frost dates are for the average when frost occurs one year in two. Killing frosts occur after the spring and before the fall date frequently enough to make the possible length Fig. 77. — Average dates of the first killing frost in the fall. of the growing or frost-free period frequently less than the average. Further, such crops as are not killed by temperatures at or somewhat below freezing, have a longer possible growing sea- son than the frost-free dates. Winter grains and grass, for example, will continue to grow in the fall after a killing frost and will begin growing in the spring and winter long before the average spring killing frost date, if favorable tempera- tures prevail. 604. Vegetative periods. — The temperature at which most field and garden crops will begin to grow is probably close to 6° (C.) or 42.8° F. Hence the growing or ''vegeta- 272 AGRICULTURAL METEOROLOGY tive" period for the crops that are not killed by ordinary frosts may be considered as that between the date in the spring when the average daily temperature rises to 43°, and the date in the fall when the mean daily temperature falls to 43°. 605. Comparison of the vegetative with the frostless period. — The vegetative or potential growing period is longer than the frostless period in all parts of the United Fig. 78. — Average number of days between killing frosts. States, except over a small area along the north Pacific Coast, as shown by Fig. 79. This difference varies from less than twenty days in a few places in the northern part of the country to over 100 days in the northern part of the Gulf states. 606. The true growing season. — The normal growing season, therefore, should be the average vegetative period and not the frost-free period, for the reasons given above. 607. Extending the growing period. — In those regions where the vegetative period usually begins a month or more before the last killing spring frost, and extends as long a time after the first fall frost, it has been profitable to protect ten- der crops from frost damage by artificial means, and thus FROST AND FROST DAMAGE 273 274 AGRICULTURAL METEOROLOGY make their possible growth period agree more nearly with that of the hardy crops. The protection of fruit and truck crops from frost is en- tirely practicable but whether economically profitable de- pends on the value of the crop saved and the expense of pro- tection. 608. When frosts occur. — Areas of high barometric pres- sure spread across the United States from the west toward the Fig. 80. — Daily weather map showing an area of high pressure with a cool wave in the Northwest that may be expected to over- spread Ohio in the next forty-eight hours with general frosts. The solid lines are drawn for equal barometer pressure while the dotted lines are drawn through places with equal temperature. The arrows fly with the wind and show wind direction. east at an average rate of 400 to 600 miles in twenty-four hours. They are usually preceded by strong northwesterly winds which cause a drop in temperature ; if it is in the winter and the fall in temperature is rapid and extreme it is termed a "cold wave," while in the summer the phenomenon is spoken of as a "cool wave." After the windy front of the high pressure area or "anti- cyclone" has passed by and the center of the high overspreads a district, it generally causes clear and comparatively quiet FROST AND FROST DAMAGE 275 air. The air is so clean and clear that it may seem very warm in the sunshine, but continues keen and cool in the shade. At night the surface of the ground and objects upon it cool rap- idly by radiation and in turn cool the lower layer of air by conduction, and, if it is in the spring or autumn, the temper- ature of the plants and of the air in contact with them may fall to the freezing point and frosts occur. Figs. 80, 81, and 82 show the movement of an area of high pressure across the Fig. 81.— The high pressure area shown in Fig. 80 is spreading southeastward and is causing general frosts in Ohio. Light, heavy, and kilUng frosts are shown by appropriate words. Lakes and the Ohio Valley that was accompanied by general and widespread frosts. 609. Local conditions favorable for frost.— The local con- ditions which indicate the central portion of an area of high pressure are clear and nearly still air with the temperature falling quite rapidly in the afternoon and early evening; with clear skies because the radiation of heat from the ground and plants is most rapid in clear weather; with nearly still air be- cause under these conditions the air arranges itself in layers with the colder heavier air at the surface of the ground, es- pecially in low places. This line of temperature variation is 276 AaUICVLTURAL MI'JTmHOLOGY so well inarkod sonuM iiuos (h;it the iVuil on the lower part of a two will 1)(' killed by frost whiles i\\r. upper piirt will escape dainnji;e nnd l)(\'ir ;i <>;()()d v.vup. 610. Principles of frost protection. — To prevent damages from frost, action must be taken to coiuiteract, so far as pos- M^y P, /9/4 Fio. S2. — The same area twenty-four hours later. It overspreads Oiiio and frosts are widespread. The temperature will rise gradually as the area moves eastward. sil)l(^ the conditions favorable for frost. Hcnco the following l)recauti()ns should be (a,k(>n: (1) Dinunish tlu^ radiation of heat at night by covering with wood, })apei-, or cloth, or by building snmdge fires that surroiuid the trees or plants with artificial clouds of smoke. (2) Locate orchards and early gardc^n crops on the hillsides and not in low places, so that the air which has been cooled by conduction to the surface of the ground will slide slowly away into tlu^ valley and be replaced by th(^ warmer horizon- tally moving air wliich ovcm'Hc^s the coldcu- air in the valleys when conditions of inversion prevail. (3) By mixing the air so as to })i'(^v(nit its forming in lay(^rs. (4) Adding lu^at to tlu^ air. Tt has been demonstrated that Plate VIII. — (Upper) The California short-stack oil heaters in place in an orange grove. (Lower) Improved tall-stack down-draft oil heaters burning at night. The lower portions of the stack are red hot and there is verv little smoke. FROST AND FROST DAMAGE 277 by building a large number of small fires in the orchard or throughout the truck fields not only will heat be added, but the lower part of the atmosphere will be kept in circulation so that laj^ers of cold air will not form. 611. Protection from frost damage by building fires. — The adding of dry heat to the air, thus warming up the cold lower layer and mixing the cold lower layer with the warmer Fig. 83. — Lard-pail type of oil heater, and one of the first invented, layer immediately above has come to be the best accepted method for frost protection. 612. Kinds of fuel. — Fires may be made of oil, coal, wood, or any other material that will burn readily. The fuel to be used in any particular orchard will depend on its rela- tive accessibility and the labor available. 613. Oil-heaters. — There are some ten to fifteen different types of oil-heaters on the market, varying from 1 to 6 gallons in capacity and costing from 20 cents to several dollars each. (Fig. 83 and Plates V to VIII.) The oil-heaters should be set at the rate of 80 to 120 to an acre. The temperature must be watched closely and when it has fallen nearly to the 278 AGRICULTURAL METEOROLOGY danger point, every third or fourth heater should be Hghted and then the others as needed. The fires should be thicker on the outside edge, especially on the windward side, and also in low places. 614. Oil consumed. — The round heaters of the lard-pail type with the top about 7 inches in diameter will burn at a rate of about one quart an hour. With fifty pots of the one- gallon capacity burning to the acre, twelve and one-half gal- lons of oil will be consumed an hour for each acre. With heaters constructed so that the burning surface can be con- trolled, the intensity of the fires can be varied as the temper- ature conditions demand. The number of hours that the heaters will be burned will vary with the season, crop, and location. If one stores 400 gallons of oil for each acre, it will allow for burning 100 one- gallon pots to the acre for twelve hours, which is sufficient for most seasons in the deciduous orchards. It is usually nec- essary to provide for longer burning periods and a much longer critical period in the citrus orchards. 615. Kind of oil. — The most desirable oil for fuel is a refinery product of about 20 to 26 degrees Baume. Crude oil is used considerably, but it is likely to contain a small amount of water, and when such does exist the oil is liable to boil over after a short time, just when the fire is needed most. Oil with a parafine base burns much cleaner than that with an asphal- tum base. Light gravity oil burns too readily, while too heavy oil does not burn clean and a large amount of soot is deposited on the trees. 616. Lighting heaters. — Special or home-made torches may be used in lighting the heaters. The time necessary de- pends on the type of heaters, kind of torches, the number of heaters lighted to the acre, and so on. Under very favorable conditions, one man can light over 500 fires in an hour, while 100 an hour would be a good number where the pots are scat- tered or do not light quickly. 617. Cost of equipment. — The initial investment for equipping a ten-acre orchard for oil-heating, including tank, cistern, heaters, and the like, under average conditions will not be far from $500, or $50 an acre. After the first year, the cost of heating including labor and fuel will approximate $3 to $5 an acre for each night. FROST AND FROST DAMAGE 279 618. Coal-heaters (see Fig. 84) cost more than the cheaper oil-heaters, but only about half as many are set to the acre. The best coal-burners hold 25 to 30 pounds of coal and will burn from four to six hours. It is considered that one ton of coal equals 100 gallons of oil in heating value. At one Ohio orchard in 1914, the temperature was kept 9 degrees higher within the orchard than was recorded outside the ^^^^^^IPIggJII^g 7^4'^--.^T 'C5*;^..;C "■■■'^^''''*| Fig. 84. — A type of coal heater that will hold about 18 pounds of soft coal. They will burn seven or eight hours. heated area with thirty-six coal fires to the acre. Oil-soaked waste and kindlings are placed in the bottom of the coal- heaters before they are filled. They are then lighted with a torch fully as fast as the oil-heaters. Coal is often placed in piles about the orchard, thus saving the cost of heaters. It must be remembered that a few large piles of coal to the acre will not furnish adequate protection, but that the more small piles the better. 619. Wood fires. — Fires have been made of old rails, brush, and cord wood. In using cord wood, the sticks are piled with the ends dove-tailed together and as these ends burn off the sticks are pushed together. About six sticks of hardwood 280 AGRICULTURAL METEOROLOGY will burn four or five hours. Wood needs more attention than either coal or oil and the fires must be started earlier. (See Fig. 85.) 620. Great care needed. — Experience has shown that one must go about orchard-heating in a throughly business- like manner. There must be plenty of fuel, men enough to keep the fires going and to make preparation for the next Fig. 85. — Wood piled for orchard heating. night's fight, and constant vigilance until the frost season is over. Care must be taken not to waste the fuel by lighting the fires too early or on nights when not needed. 621. Critical temperature. — Thermometers should be dis- tributed throughout the orchard and watched closely, and when the temperature approaches the danger point the light- ing should be begun in the lowest part of the orchard. If the temperature is falling slowly, the fires need not be started until the temperature is very close to the danger point. This is especially true with oil-heaters as the effect of the burning oil is almost immediately noticed; it takes longer for the coal and wood to get started. If the temperature is falling rapidly, FROST AND FROST DAMAGE 281 however, and the conditions seem to favor a low record, the fires must be lighted while the temperature is still several de- grees above the danger point. (See Table 11 for data show- ing the critical point for many of the fruits.) Tender truck crops need to be protected from freezing temperatures also. 622. The lowest temperature just before sunrise. — Fig. 86 shows a thermograph record from May 11 to 18, 1914. It was quite warm on the 11th, the curve indicating a temper- ature of 80°. A cool wave reached the region of the station before noon of the 12th and there was a sharp drop in tem- perature. There was little variation on the 13th, but from the 14th to 17th typical radiation conditions prevailed. The temperature rose to between 60° and 70° during the daytime Fig. 86. — Record made by a self-recording thermometer May 11 to 18, 1914, at Delaware, Ohio. under bright sunshine, but fell nearly or quite to freezing at night with free radiation. It is under conditions like those of the 14th to 17th that frosts are likely to occur and, as shown by the record, the lowest temperature will be reached just before sunrise. 623. Protection by heating possible. — Experience has conclusively proven that the temperature can be kept above the danger point by orchard-heating when otherwise it would fall low enough to cause damage to fruit and truck. Arrangements can be made to receive frost warnings by writing the nearest Weather Bureau Office if an effort is made to protect fruit or truck from frost damage. LABORATORY EXERCISES 1. Paragraph 603. Obtain daily mean temperature and killing frost data from the local Weather Bureau and compare the frostless and vegetative periods. 282 AGRICULTURAL METEOROLOGY 2. Paragraph 605. If the vegetative period is considerably longer than the frost-free period, what local crops might profitably be pro- tected from early or late frosts? 3. Paragraphs 610 to 619. Carry out some tests of frost protection, particularly to truck or small-fruit Crops, by covering or heating. 4. Paragraph 621. The influence of topography on night tempera- ture should be ascertained by exposing thermometer at different ele- vations. REFERENCES A Study of the Effect of Freezes on Citrus in California. H. J. Webber and others, California Experiment Station Bulletin No. 304. Avoidance and Prevention of Frosts in the Fruit Belts of Nevada. Church and Ferguson, Nevada Agricultural Experiment Station Bulletin No. 79. Freezing of Fruit Buds, The. F. L. West and N. E. Edlefsen, Utah Agricultural College Experiment Station Bulletin No. 151. Forecasting Frost in the North Pacific States. E. A. Beals, U. S. De- partment of Agriculture Bulletin No. 41. Frost and the Growing Season. Atlas of American Agriculture, Office of Farm Management. Frost and the Prevention of Damage by It. Floyd D. Young. Farmers' Bulletin, 1096, April, 1920. Frost and Temperature Conditions in the Cranberry Marshes of Wis- consin. Henry J. Cox, Weather Bureau Bulletin T., 1910. Frost Data of the United States. P. C. Day, Bulletin V of the Weather Bureau, Department of Agriculture. Frost in the United States. Wm. Gardner Reed, Proceedings of the Second Pan American Congress, 1916. Frosts in New York. W. M. Wilson, Cornell University, Agricultural Experiment Station Bulletin No. 316. Hardiness of Fruit Buds and Flowers to Frost. Garcia and Rigney, New Mexico Agricultural Experiment Station Bulletin No. 89. KiUing of Plant Tissue by Low Temperature. W. H. Chandler, Mis- souri Agricultural Experiment Station Research Bulletin No. 8. Papers on Frost and Frost Protection in the United States. Monthly Weather Review, October, 1914. Protection from Damage by Frost. W. G. Reed, Geographical Review, Vol. I, 1916, No. 2. Studies in the Formation of Frost. D. A. Seeley, Monthly Weather Review, August, 1918. Relation of Weather to the Setting of Fruit, The. Hedrick, New York Agricultural Experiment Station Bulletin No. 299. Variation in Minimum Temperatures due to the Topography of a Mountain Valley in Its Relation to Fruit Growing, Batchelor and West, Utah Agricultural Experiment Station Bulletin No. 141. CHAPTER XII VALUE OF LIGHTNING-RODS There was a time when lightning-rods were a fad and the Hghtning-rod agent flourished and waxed fat. But because he insisted on accumulating the good things of the land too rapidly there soon came a second period when shot-guns were kept loaded and standing beside the outside door because the lightning-rod agent became more to be feared than the light- ning. But the lightning-rod that had been put up stayed up and it began to be noticed that those which had been installed in an honest and workmanlike manner furnished protection, while all around buildings without such protection were being destroyed by lightning. This has led fire-protection agencies, appalled by the immense fire loss, to inquire more fully into the possible value of lightning-rods as a protection. 624. Thunder-storms. — All the features of thunder- storms point to their dependence on a convectional overturn- ing of the atmosphere. Thunder-storms usually occur wher- ever there is a rapidly rising current of moisture-laden air. Condensation goes on rapidly in such a rising mass of air as soon as the dew-point temperature is reached and at such times electricity accumulates very rapidly. As clouds form, different clouds or parts of the same cloud may be charged with various kinds of electricity, negative or positive. Great changes in electrical potential are caused which may result in lightning. 625. Where thunder-storms occur. — Thunder-storms oc- cur most frequently in warm regions and are commonest in spells of warm summer weather and in the afternoon shortly after the warmest part of the day. In the United States the greatest number occur in the east Gulf states where the average days with thunder-showers each year will be close to sixty. In Missouri and eastern Kan- sas it will average over fifty, while in the whole central valley country from the Appalachian to the Rocky Mountains and 283 284 AGRICULTURAL METEOROLOGY from South Dakota and southern Minnesota and Wisconsin to the Gulf the average number each year is over thirty. In New England, upper Michigan, and practically all of the region in and west of the. Rocky Mountains, except in New Mexico and Arizona, the average annual number of thunder-storm days is less than twenty. In the Pacific Coast states they are very rare. 626. Nature of lightning. — Lightning is an electric spark on a tremendous scale. It occurs between clouds more fre- quently than between cloud and earth. The length of the flash between the cloud and the earth is usually not more than one mile in length, while within clouds it may be twenty miles in length. Lightning flashes usually consist of a number of successive discharges which follow each other with a very short interval between. In one case of a flash consisting of five successive discharges, the total time from the first to the last was found to be 0.2447 second, while the intervals be- tween the successive discharges were found to be 0.0360, 0.0364, 0.0283, and 0.1440 second, respectively. One photo- graph showed forty distinct discharges in a single flash. 627. Damage by lightning. — Damage by lightning is mechanical as well as thermal. Not only is the damage caused by main discharges, but currents are induced in nearby metal objects and conductors and these often produce ad- ditional damage. It is probable that most of the unusual re- sults in a lightning flash are due to these induction effects. This will be shown by a fire being started in inflammable ma- terial between two nearly parallel wires or rods. One example reported is of a fire in a flour-mill where it was evident a fire started on a separator between the fan- shaft and the drive shaft bearings. In this case the mill had a metal roof and was iron-clad, a protection that is considered to be absolute as far as any damage to the exterior of the building is concerned. This same writer believes that these induction effects between the wires on baled hay are respon- sible for many otherwise unexplainable fires in properly pro- tected barns or warehouses. Another writer, secretary of a company carrying risks in farm propert}^ of fully $42,000,000, states that all of the losses and damages by lightning which they have had on rodded buildings have iDeen traced to some metal parts, which were VALUE OF LIGHTNING-RODS 285 not connected to the lightning-rod. They find that the tele- phone line in houses is the most dangerous thing with which they have to contend. He states that they find lightning will jump ten, twelve, arid fifteen feet from the lightning-rod to the telephone wire and the same from the telephone line to the hghtning-rod. They now advocate placing the ground rod on the house as near as possible to the telephone wire without touching it. 628. Loss by lightning greatest in rural districts. — The property loss by lightning in the entire country averages ap- proximately $8,000,000 each year, the greater part of which occurs in rural districts. In the central part of the country, the loss and damage by lightning is far greater in the country than in the cities. The Indiana Fire Marshal states that 75 per cent of all lightning losses occur in the rural districts which contain but 47 per cent of the population. He states further that in 1913, 92 per cent of all barns damaged by light- ning were in the country and that 69 per cent of all barn losses were total. In the case of dwellings, 52 per cent damaged or burned by lightning were in the country and 48 per cent in the city. It is stated on good authority that about four times as many barns are fired by lightning as houses. 629. Office of the lightning-rod. — There is a nearly con- stant interchange between the electricity in the earth and that in the atmosphere and one of the offices of the lightning- rod is to furnish a path for the quiet discharge or interchange of this electric current. The second office of the rod is to fur- nish a path for the disruptive discharge between the clouds and the earth when the potential reaches the breaking point. 630. Value of lightning-rods. — In 1914 the author sent letters of inquiry to over 1100 Mutual Fire Insurance Com- panies doing business in forty-four different states mostly in the rural districts. They were requested to report in detail the actual records from their books. Replies from 130 different companies doing business in fif- teen states showed that they had kept their records in such detail that full information could be given. These companies had about 350,000 farm buildings insured, valued at close to $300,000,000. These reports were tabulated and are sum- marized in the table following. 286 AGRICULTURAL METEOROLOGY o I ^ i- y^ Ox y^ \-L ^,^ CO O O ?S CO to CO h-' J-* O to CO O) ^^fi. O) J-' C^ CO O O Oi -vj Cn CO Number of insurance com- panies reporting Number of farm buildings in- sured <:^ i^'ll ^tx Nufnber of buildings burned ^^ o^ I^ § Z'"^'^* "^2/ cause O M CO Ci Number of buildings struck by lightning ^ g o 00 Number struck, only damaged h-. t^ l_a -J Oi Oi Oi -^ Or lO (4^ ^ to 4i^ lO o h-' 00 t4^ to H- C5 W o 00 ^ ~o "oo "co ^ to 00 H+^ J-'J^:) CO CO S 2 o o o o o o o o o o m jr' I-' oi CO CJ 00 -4 Ci .50 Oi to JO CO '^5 00 ~0 to Oi rfi. o O CO rfi. CO rfi- ^ S CO 00 ;j ^j-4 to ^rf^ Or g Cn 4^ 00 g ^ to to M Oi s Cn CO CO ^ Cn hfi' H- r^ Number struck and burned Number struck that had light- ning-rods Number with lightning-rods struck and damaged Number with lightning-rods struck and burned Total risks on farm buildings Total claims paid from all fire loss on farm buildings Total claims paid due to lightning Total claims paid due to light- ning on rodded buildings Percentage of buildings rodded I o > o o tr" *-Q q > *j^ ^§ "■^ a VALUE OF LIGHTNING-RODS 287 631. Lightning-rods as a protection to buildings. — This table shows that the total number of buildings struck by lightning in 1912 and 1913 was 1845. Inquiry developed the fact that close to 31 per cent of all of the buildings insured by these companies are equipped with lightning-rods. Hence, if rodded buildings were just as likely to be struck by light- ning as unrodded ones, there would be 31 per cent of the 1845 buildings that were struck by lightning that would have rods on them. As a matter of fact, however, only sixty-seven of the buildings struck had rods of any kind. The number of rodded buildings that were struck, therefore, was only 10 per cent of the expected number, demonstrating the fact that the efficacy of the lightning-rod in actually preventing dam- aging lightning strokes is 90 per cent. In a report covering the past five years, fifty-one different companies having nearly 95,000 buildings insured, had 660 buildings struck by lightning, only twenty-one of which had lightning-rods on them. As fully 34 per cent of their build- ings are rodded, the expectation would be that 34 per cent of 660 or 224 would be rodded. But as only twenty-one were rodded instead of 224, or only 9 per cent, it shows that one may expect that out of every 100 farm buildings struck by lightning nine of them will be equipped with lightning-rods and ninety-one will not have rods. A table made up from sixty-seven different companies in Missouri, Illinois, and Ohio showed practically the same efficiency. Five companies doing business in Illinois, Missouri, and Nebraska with over 18,000 buildings insured, made reports covering a longer period of years, the shortest being thirteen years and the longest twenty-five years. They have had no building burned or even materially damaged by lightning that was equipped with rods, and they report over 50 per cent of their buildings rodded. T'his is an efficiency of 100 per cent. This finding of the efficacy of the lightning-rod in prevent- ing damaging lightning strokes is substantiated by the results of an inquiry by W. H. Day of the Ontario Agricultural Col- lege. His inquiry covered Ontario, Iowa, and Michigan and included several years. He found the efficacy of the light- ning-rod m preventing lightning strokes to be from 92 to 99.9 per cent. 288 AGRICULTURAL METEOROLOGY 632. Damage to rodded buildings. — Occasionally a rodded building is struck by lightning, but the properly in- stalled lightning-rod is of very great value in preventing dam- age. , ^ The table shows that the total claims paid on farm build- ings due to lightning, in 1912 and 1913, was $336,171. Inas- much as 31 per cent of these buildings insured by these com- panies were rodded, a loss would be expected on rodded buildings of 31 per cent of $336,171 or $104,213, but in fact the total claims paid for lightning damage on rodded build- ings during the two years was only $13,053. In other words, the actual loss was only 12 per cent of what would have oc- curred if the lightning-rods did not serve as a protection. The total number of buildings burned by lightning in 1912 and 1913 as reported by these companies was 407, and of these only nine were equipped with lightning-rods, or only 2 per cent. Of those struck that had rods, only 5 per cent were burned and the other 95 per cent simply damaged : thus show- ing that the danger of a building being burned by lightning that is equipped with lightning-rods is exceedingly slight. A further study of the reports shows that when struck and damaged by lightning but not burned down, the average dam- age to a building was less than $10 on those equipped with rods and very nearly $200 when not so equipped. 633. Material for lightning-rods. — Lightning-rods may be of iron, copper, or aluminum and either will be satisfactory as a conductor. As iron is not so good a conductor as copper, it is thought to carry a lightning flash more safely, and be- sides it has the advantage of having a higher fusing point. Iron rods must be heavily galvanized and kept painted fre- quently and for this reason should not be used in locations difficult of access. If single-strand iron rods are used, they should be No. 2, No. 3, or No. 4 (B. and S. gage) depending on the size of the building; No. 2 is 0.257 inch in diameter or about twice the size of an ordinary telegraph wire which is No. 9; No. 3 is 0.244 inch and No. 4 is 0.225 inch in diameter. Star section rods are preferred by man}^ The Michigan Agricultural Experiment Station recom- mends the use of 3/8-inch seven-strand iron cable as being easy to handle, inexpensive, and wholly satisfactory. The VALUE OF LIGHTNING-RODS 289 important thing seems to be to have it heavily galvanized and kept painted. , • -j 634. Copper rods.— The best type of a copper rod is said to consist of bundles of small wires twisted tightly together. A steady electric current flows through every part of a con- ductor, but when the current is variable and exceedingly rapid the flow may be confined to a film very near the surface. To carry a lightning discharge, therefore, the rod should have as large a surface as possible. A twisted rod with thirty wires each 0.0425 inch in diameter has about five and one- half times the surface of a round solid rod with the same amount of material. The National Board of Fire Underwriters recommends that on residences, barns, stables, stores, and similar buildings where the maximum height of any point does not exceed 60 feet, copper cable be used, weighing not less than 3 ounces a foot and no single wire being less than 0.046 inch m diameter. In the case of taller and larger buildings, they recommend the cable to weigh not less than 6 ounces a foot. 635. A continuous conductor necessary.— The all-impor- tant thing seems to be to have a continuous conductor from the highest points on the building to permanently moist earth beneath. The kind of material and the size of the rod does not seem to be so important as frequent inspection, good groundings, and constant care to see that there are no poor or broken joints or rusted and broken connections. 636. Points above all projections. — Points should extend above all chimneys or other roof projections and should be placed at each gable end and at intervals of 25 to 30 feet along the ridge. There should be two grounds to all rod systems and if the buildings are 100 feet or more in length, three or more down rods. All cables should be connected in one s^^s- tem. Insulators should not be used but the rod fastened di- rectly to the sides of the building. All heavy masses of metal in the building should be connected to the rod, but the rods should be kept as far away as possible from gas-pipes or lead water-pipes. . 637. Grounding the rods.— The earth connection may be a square sheet of copper 1/16 inch in thickness and not less than 3 feet square. This must be buried in moist earth even if one has to go down 10 or 12 feet. Probably the most eco- 290 AGRICULTURAL METEOROLOGY nomical and at the same time satisfactory grounding is made with cast iron or copper rods extending into the earth from 6 to 10 or more feet, or to a point well below the foundation walls of the building to be protected. Farmers' Bulletin 842 illustrates satisfactory methods for grounding wires, connecting exterior and interior metal work, ■^ Fig. 87. — Lightning-rod on a small general barn, erection of roof points, and the like, in a very complete man- ner. (Figs. 87, 88.) 638. How spliced. — When splices are necessary, the ends must be fastened solidly together and if possible riveted and soldered. When there is an imperfect connection, the elec- trical resistance will be so great that the electricity is likely to leave the rod and damage the building. Metal-covered roofs should be connected with ground wires from at least two corners by riveting and soldering and then run to moist earth. VALUE OF LIGHTNING-RODS 291 639. Care in installing. — While lightning-rods must be put up in a workmanlike manner, their installation involves no more wonderful or mysterious processes than building a fence or digging a well. The statement by some lightning-rod agents that no one but special scientists versed in all of the laws of electricity should do the work of putting up lightning conductors is Fig. 88. — Method of placing points and connecting rods on a farm- house to protect from hghtning. about as sensible as to say that no one but a professor of ge- ometry should be allowed to lay brick. And not only that but any professional in the lightning-rod business who advo- cates that his system is the only one scientifically correct and reliable, while all others are worthless and dangerous, invites the suspicion that he is himself a fakir. The installation of a proper rod is not and need not be ex- cessively expensive. By the exercise of ordinary common sense and with the knowledge that electricity demands a con- tinuous path to the moist earth, a satisfactory rod can be put up without serious trouble. 292 AGRICULTURAL METEOROLOGY 640. Loss of live-stock. — The loss of live-stock near wire fences is very great. It may be reduced by grounding wire fences by means of galvanized iron pipes or posts at intervals of about 100 yards or by attaching wires to the posts at about the same distances and letting them extend well into the ground. Care must be taken to see that these ground wires are in contact with each fence wire, and that they go into moist ground. The electrical continuity of the fence should be broken at intervals also by inserting sections of non-con- ducting wood in place of the fence wire. LABORATORY EXERCISES 1. Paragraph 630. An inquiry of the local Mutual Fire Insurance Companies regarding losses on rodded and unrodded buildings would give some valuable data. 2. Paragraph 637. Copies of Farmers' Bulletin 842 should be ob- tained for detailed instruction in instalhng lightning-rods. 3. Paragraph 640. An inquiry of local stock-growers would develop some interesting and valuable data regarding loss of stock near un- grounded wire fences. REFERENCES EfRciencj' of Rods in Preventing Lightning Damage, The. W. H. Day, Ontario Agricultural College Bulletin 220. Lightning and Lightning Conductors. J. Warren Smith, Annual Report Mutual Fire Insurance Association, 1915. Modern Methods of Protection against Lightning. R. N. Covert, Farmers' Bulletin S42. Protection of Life and Property against Lightning, Bureau of Stand- ards, Technologic Paper No. 56. INDEX The numbers refer to the page Absolute humidity, 9. Agricultural climatology, 28. meteorology, 23. Agriculture, 63. Alfalfa, 92, 239-241, 251, 252. seed and frost, 240, 241. water requirements, 92. Aliquot, 77, 78. Almonds, 125, 126, 139. American Indian and corn, 149. Anticyclone (high pressure area), 262-264, 274. Aphis, 256. Apples, 96, 126-129, 139, 253, 260. Apricots, 129, 130, 139. Asparagus, 219. Atmosphere, 1, 2, 4, 8, 15, 226. composition, 1, 2. circulation, 15. how cooled, 4. how warmed, 4. Avocado (alligator pears), 130. Bacteria of the soil, 79, 84. Barley, 64, 91, 93, 142, 143. critical period, 143. temperature limits, 64. water requirements, 91, 93. Barometer, 3. Beans, 96, 97, 217. in California, 97, 217. Beets, 92, 96, 217. Bioclimatic law, 29. an aid in farm management, 30. Bitter-rot, 253. Boll-woovil, 122, 123. Broom-corn, 181. Buckwheat, 91, 93, 143, 144. water requirements, 91, 93. Cabbage, 217. Cantaloupes, 215. Carbon-dioxide, 1, 76, 95. Carbon dioxide, liberation from plants by daylight, 95. by temperature, 76. Carnations, 67. Carrots, 217. Cassava, 215. Castor beans, 215. Cattle-tick, 256. Cauliflower, 217, 218. Celery, 218. Chard, 218. Cherries, 130, 139. critical temperature, 139. Chinch-bugs, 255, 256. Chinooks, 19, 97. Citrus fruits, 136-139. lemons, 96, 137, 139. hmes, 137. oranges, 136, 137, 139. pomelos (grape-fruit), 138. Climate, and crops, 61. and farm operations, 101. and man, 28. and number of crops, 103. continental, 61, 62. depends on, 61. important factors: moisture, 93. sunshine, 93. temperature, 64. wind, 97. limited by temperature, 63. main factors in, 64. marine, 61, 62. mathematical, 61. mountain, 61, 62. natural, 61. physical, 61. solar, 61. three classes, 61. zones, 63. 293 294 INDEX Climatic limits of crops, barley, 142. buckwheat, 143. clover, 241. corn, 144-146. cotton, 101, 108. cowpeas, 243. flax, 123, 124. fruit, 126, 129-131, 133.. millet, 242. oats, 64. potatoes, 222, 223. rice, 179 rye, 180, 181. sugar-beets, 245, 246. sugar-cane, 243. timothy, 242. tobacco, 248. vegetables, 215-221. wheat, 63, 64, 101, 181, 183. Climatic zones, 63. Clouds, 11. local weather signs, 267. versus sunshine, 93. Clover, 241, 242. Coal-heaters, 279. Collards, 218. Condensation, 11, 283. Conduction, 4. Continental climate, 61, 62. Convection, 4, 5. Cool-season crops, 106, 215. barley, 142. buckwheat, 143. potatoes, 222, 223. vegetables, 216-219. Copper lightning rods, 289. Corn, an American crop, 145. belt, 101. climatic factors, 144-147. correlation coefficients, 158-160, 164-168. four great corn States, 153-155. frost, 170, 171. germination and temperature, 149. injury to seed corn, 171. in south temperate zone, 172, 173. pollination and drought, 171. rainfall, 37, 38, 40, 41, 54, 144- 146, 150-170. Corn — Continued critical period, 151, 153, 158- 166. near blossoming, 165. for short periods, 158-160, 164, 165. in July, 151-157. most effective, 166-168. the most important factor, 151. rainfall and temperature com- bined, 155-157. raised by American Indians, 149. rate of growth of seedling shoots, 69-71, 149. rate of seeding, 172. sunshine-hour, degree, 94. temperature limits, 64. thermal and rainfall constants and yield, 161, 164, 165. transpiration from, 85, 150. relating to drought, 172. two seasons compared, 169, 170. water requirements, 90, 91, 93, 150, 151. weather during different periods of growth, 160-166. when planted, 146, 147. best dates for, 150. in relation to frosts, 147. in relation to temperature, 147. where grown, 144, 145. yield in Ohio, 54, 56. affected by July rain, 57, 155- 158. zero of vital temperature, 68. Correlation, 34. coefficient, 53. curve fitting, 41, 46. dot chart, 37. least squares, 41, 46, 47. normal equations, 46, 49. partial or net, 5S. proper method, 36. star point method, 47, 48. usual method, 34. when mathematical correlation should be made, 41. Correlation coefficient, definition of, 53. how calculated, 54. INDEX 295 Correlation coefRcient — Continued in showing relation between weather and crop yield, 53. probable error, 57. symbol used for (r), 57. theory of, 53. value of, 57. weather and apples, 126, 128. barley, 143. clover, 241, 242. corn, 158-160, 164-168. cut-worms, 256. hay, 238, 239. hessian fly, 256. maple products, 247. oats, 175, 178. potatoes, 224, 227, 228, 231- 233. rye, 180. sugar-beets, 247. tobacco, 250. wheat, 196, 197, 199, 200, 202, 208, 211. Cost of oil heating, 278. Cotton, belt, 101. ' climatic limits, 101, 108. temperature principal factor, 108, 109. effect on maturity, 111. dates of planting and harvesting, 109, 110. effect of two different seasons, 120-122. general weather effects, 1 1 5. seasonal weather, 116, 117. ginning and temperature, 111, 112. insect pests, 122, 123. rainfall influence, 111-121. in July and August, 117-119. in winter, 118, 120. sunshine. 111. temperature, 108-121. water requirements, 92, 93. weather-cotton equation, 113-115. where grown in the United States, 108, 109. zero of vital temperature, 68. Cowpeas, 243. Cranberries, 130, 131. critical temperature, 139. Critical periods of growth, 24. barley, 143. corn, 151, 153, 158-166. for definite climatic districts, 106. fruit, 138-140, 280, 281. hemp, 125. potatoes, 228-233. wheat, 191. Crop zones, 101, 102. Cucumbers, 215. Currants, 130. Curve fitting, 41, 45-47, 49. Cutworms, 249, 255, 256. Cyclone (low pressure area), 262- 264. Dates, 67, 131. Dates of seeding and temperature, 68. corn, 147. oats, 68. potatoes, 222. Daylight, effect of, 95. on rate of liberation of carbon dioxide, 95. on sugar content of beets, 96. pigments, 95. hours at different latitudes, 94, 95. Dew, 14. Dew-point, 10, 283. depression of the, 10, 42, 43. in connection with predicting mininmm temperatures, 47. Diseases of crops as affected by weather, apples, 128, 129, 253, 260. cucurbits, 253. flax-wilt, 254. grapes, 132. peaches, 134. potatoes, 233-236. late blight, 234, 236, 253. spread bj'' wind, 254. strawberries, 136. smuts, 254, 255. tobacco, 250, 251. weather terms relative, 253. wheat, 185. rust, 185, 191, 254. 296 INDEX Dot charts, 36, 37, 40. Drought, defined, 84. pollination of corn, 171. transpiration of corn, 172. Dry farming, 104. Effective temperatures, 67, 68. three summation processes, 68-73. Eggplants, 215. Equations, 41, 46, 47, 49, 51. partial correlation, 58. weather-cotton, 113. Evaporation, 5, 9. amoimt of, 85-87. compared with transpiration, 85. determines efficiency of rainfall, 87. from the soil, 88. important factor in dry rcgif)ns, 85. Exponential system, 68, 69, 72, 74. Farm operations, and climate, 101. bioclimatic law, 30. butter and cheese making in Wis- consin, 102, 1C3. change in, 102. climate and number of crops, 103. distribution of rain, 103. dry-farming, 104. length of growing season impor- tant, 103. woatlier risk, 104. Fiber crops, cotton, 108-123. (See cotton.) flax, 123-125. (See flax.) hemp, 125. (See hemp.) Figs, 131. Flax, fiber versus seed, 124. in North Dakota, 124, 125. relation to weather, 123, 124. water requirements of, 92, 93. where grown in North America, 124. wilt, 254, 255. Fog, 97, 217, 267, 268. Forage crops, alfalfa, 239-241. Forage crops — Continued clover, 241, 242. cowpeas, 243. hay, 102, 236-239. millet, 242. rape, 242. sorgo, 242. timothy, 242. weather and yield, 236-243. Forecasting the weather. (See weather forecasts.) Frost, alfalfa seed, 240, 241. average killing dates, 270, 271. conditions for, 274-276. corn, 170, 171. critical temperatures for fruit, 138-140, 280, 281. flax, 124. fruit, 126, 131, 133, 134, 140. growing season, 271, 272. hemp, 125. killing of plant tissue, 140. limits growing season of cotton, 109. most damaging when fruit is wet, 140. not expected in cloudy weather, 5. oats, 178. protection from, 276. by fires, 277. coal heaters, 279. oil h'eaters, 277, 278. wood fires, 279, 280. risk of in farm operations, 104. spring dates agree with corn planting, 147. vegetative periods, 271-273. with temperature inversion, 5. Fruit, 125-141. critical temperatures, 138, 139, 141. leaf buds versus fruit buds, 127, 128. sunshine, 96. Germination and temperature, buckwheat, 144. corn, 149. oats, 68. Gherkins, 216. INDEX 297 Glaze, 14. Gooseberries, 130. Grains, water requirements of, 89-93. weather and yield, 14.'. winter killing, 208, 209. Grain sorghums, 181. Grapes, 131-133. critical temperatures, 132, 139. Grasshoppers, 255. Growing season, barley, 142. buckwheat, 143. corn, 145-149. cotton, 109. (See cotton.) flax, 124, 125. hemp, 125. in relation to frost, 271, 272. oats, 175. vegetables, 215, 216. Hail, 14. shooting hailstorms, 15. Halos, 267. Harvesting dates, corn, 148. cotton, 110. flax, 125. oats, 173, 174. strawberries, 135. wheat, 185-190. Hay and forage crops, alfalfa, 239-241. belt, 101, 102, 236. clover, 241, 242. cowpeas, 243. millet, 242. rainfall and yield, 238, 239. rape, 243. sorgo, 242. timothy, 242. water reqmrements, 237, 238. weather and jdeld, 236-243. Hemp, 125. Height of the atmosphere, 2. Hessian fly, 186, 189, 211, 256. Honey, 247, 248. Hops, 219. Humidity, 9. absolute, 9. varies with the temperature, 9. Humidity — Continued local weather signs, 265, 266. relative, 10. use in predicting minimum temperatures, 47. varies inversely with the tem- perature, 10. Hurricanes, 17, 18. Hygrometric equations, 51. Hyperbola, 53. Insect pests, cattle-tick, 256. chinch-bugs, 255. codling moth, 129. cotton, 122, 123. boll weevil and weather, 122, 123. red spider, 122. cutworms, 249, 255, 256. grasshoppers, 255. hessian fly, 186, 189, 211, 256. oat aphis, 256. parasites, 256. white grub, 256. Insolation, 4, 5. Installing lightning rods, 289- 291. Instruments, meteorological, anemometer, 19. barograph, 3. mercurial barometer, 3. psychrometer, 10. rain gage, 7, 12, 13. records valuable, 31. thermometers, 7. thermometer shelter, 7. thermograph, 8. Iron lightning rods, 288. Irrigation, in humid regions, 93. potatoes, 224. sugar-beets, 246. rice, 180. wheat, 191. Kafir, 181. Kale, 218. KilHng frost dates, 270, 271. Kohlrabi, 218. 298 INDEX Laws of the weather, 261, 262. Least squares, 41, 46, 47. calculation of straight line equa- tion, 41, 45, 46. Lemons, 137, 139. effect of sunshine, 96. Lettuce, 218. Light, or sunshine, important meteorological factor, 93. Lightning, 283, 284. damage by, 284. loss greatest in rural districts, 285. loss of live stock, 292. to rodded buildings, 288. rods, 283. continuous conductor neces- sary, 289. grounding, 289, 290. installation, 291. material for, 288, 289. office of, 283. points, 289. splicing, 290. value of, 285-287. Limes, 137. Lissner's law, 77. Lissner's Aliquot, 77, 78. Local weather signs, 265-267. Maple sugar and sirup, 247. Marine climate, 61, 62. Mathematical correlation, 41. Mathematical equations, 61. Melons, effect of sunshine, 96. Meteorology, 1. Minimum temperature predictions, 41, 47, 48. Millet, 89, 93, 242. Milo, 181. Moisture (see Rain), in the atmosphere, 28. condensation of, 11. depends upon the temperature, 9. essential to life, 8. measuring the amount, 10. in the soil, 84. value of, 80. Moon, 268. Mountain climate, 61, 62. Muskmelons, 216. Mustard, 218. Native vegetation a key to field crops, 29. Natural vegetation and farm oper- ations, 30. Nitrogen, 1. Normal equations, 46, 49. Oats, critical period, 177, 178. harvesting, 175. rainfall, 175-179. range in United States, 173, 174. seeding, 173, 175. temperature at, 173. temperature, 175-179. temperature limits, 64. water requirements, 91, 92. winter, 175. zero of vital temperature, 68. Oil heaters, 277, 278. oil consumed, 278. torches for lighting, 278. Okra, 216. Olives, 133. Onions, 218. Optimum temperature for growth of maize seedlings, 70-72, 149. Oranges, 136, 137, 139. effect of sunshine, 96. Oxygen, 1. Parabola, 46. calculation of, 49. equation for, 47. practical application of, 52. in predicting minimum tempera- tures, 50, 51. must fit the data, 52. Parsley, 218. Parsnips, 218. Partial correlation, 58. Pasture belt, 102. Peaches, 133, 134. critical temperatures, 133, 134, 139, 140. temperature and trees, 134. INDEX 299 Peanuts, 216. Pears, 134, 139. Peas, 218. effect of sunshine, 96. Peppers, 216. Phenological records, 31, 162, 229. Physical cUmate, 61. Physiological summation indices, 68-72, 75. Phytopthora infestans (late blight of potatoes), 234-236. affected by moisture, 234. affected by temperature, 234-236. Planets, 268. Plants and weather, aliquot, 77, 78. bioclimatic law, 29. conditions for growth, 23. result of complex factors, 106. critical periods, 24. how determined, 24, 25. value of, 25. development depends on a con- stant aliquot, 77, 78. factors must be in right propor- tion, 23. growth a function of weather and other factors, 107. importance of temperature, 29, 64. liberation of carbon dioxide, 76, 95. light, 95. moisture-temperature efficiency index, 72, 73. optimum conditions, 78. periods of growth and tempera- ture, 64. periods of rest, 64, 65. rainfall, 84. requirements vary, 23. seasonal development, 29. sunshine, 95. temperature and distribution, 64. water requirements, 88. Planting dates, corn, 146, 147. cotton, 109. flax, 124, 125. hemp, 125. oats, 173, 174. potatoes, 222. Planting dates — Continued tobacco, 248. vegetables, 219, 220. wheat, 185, 186, 188, 190. to escape hessian fly, 186, 189. Plant temperature, 74. affected by sunshine, 95. as affected by pigments in plants, 76. as compared with air tempera- tures, 74, 75. difficulty of comparing, 76. fluctuations rapid, 77. Plums, 134, 135, 139. rate of blossoming, 77, 78. Polar belt, 63. Pollen, effect of sunshine, 96. Pollination, corn, 171. clover, 243. Pomelos (grapefruit), 138. Potatoes, critical period of growth, 228-233. near blossoming, 231. diseases, 233-236. late blight, 234, 236. harvesting dates, 223. planting dates, 222. relation to temperature, 222. range in the United States, 221, 222. relation of weather to yield, 34- 36, 224-228. seed, 252. temperature and yield, 40, 223, 225. cool favorable, 40, 223, 225- 228, 231-233. temperature, limits of, 64. temperature requirements, 222, 223. thermal constants, 230, 231. water requirements of, 92, 223, 224. Precipitation, dew, 14. frost, 14. glaze, 14. hail, 14. rain, 11, 12, 14. (See also rain.) 300 INDEX Precipitation — Continued sleet, 13. snow, 13. Pressure varies with altitude, 2. Probable error, 57. Proso, water requirements of, 89, 93. Protection from frost, 276. (See frost.) by fire, 277. coal, 279. oil, 277. wood, 279, 280. Prunes, 135, 139. Psychrometer, 10. Pumpkins, 216. Radiation, 4, 5, 275, 276, 281. from the soil, 79. Radishes, 218. Rainfall, cause of, 11. determines the productiveness of a region, 80. how measured, 12. increases with altitude on wind- ward side of mountain, 12. intensity of as affecting crops, 14. in the United States, 81-83. percentage during the growing season, 82, 83. rain making, 14. tabulation, 12. value of, 80. Rain in relation to, alfalfa, 239, 240. almonds, 126. amount per acre, 82. and temperature combined, 155- 157. apples, 126-128. apple diseases, 128, 129. apricots, 129. barley, 143. boll weevil, 122, 123. buckwheat, 143, 144. clover, 241, 242. codling moth, 129. cotton. 111. (Soe cotton.) corn, 37, 144. (See corn.) Rain in relation to — Continued correlation with yield, 158. (See correlation coefficients.) dates, 131. drought, 84. efficiency affected by evaporation, 87. farm management, 103, 104. flax, 124. (See flax.) grain sorghums, 181. grapes, 132. hay, 238, 239. hemp, 125. honey, 247. insect damage, 255, 256. millet, 242. most important factor, 151. oats, 175. (See oats.) olives, 133. oranges, 137. peaches, 133, 134. plant diseases, 253, 254. plant growth, 84. potatoes, 223. (See potatoes.) rice, 179, 180. rye, 180, 181. seeds, 251, 252. strawberries, 135. sugar-beets, 244, 246, 247. sugar-cane, 243, 244. timothy, 242. tobacco, 249-251. vegetables, 215-219. wheat, 183. (See wheat.) yield of corn, 37, 38, 40, 41, 54. (See corn.) Raisins, 131, 260. Rape, 243. Relative humidity, 10. use in predicting minimum tem- peratures, 47, 49. varies inversely to the tempera- ture, 10. Remainder process, 68, 69, 72, 73. Rhubarb, 219. Rice, temperature limits of, 64, 179. water requirements of, 92, 93, 179, 180. where grown, 179. Root rot of tobacco, 251. INDEX 301 Rose, American Beauty, affected by sunshine, 97. Rye, 180, 181. water requirements of, 92, 93. Salsify, 219. Saturation, 10. Seedling shoots of maize, 69-71, 149. Seeds, 251, 252. alfalfa, 240-242, 251, 252. effect of weather on, beans, 251. peas, 218, 251. from dry regions best, 251. germination of, buckwheat, 144. corn, 149. onion, 252. potato, 252. wheat, 252. Seeding corn, rate of, 172. Semi-arid regions, farming in, 93. Sheep shearing and lambing, 260. Shooting hailstorms, 15. Simultaneous equations, 46. Sleet, 13. Smuts, 254, 255. Snow, 13. and wheat, 202, 203. Soil moisture, 84. affects activity of soil bacteria, 84. affects plant growth, 84. direct source of water supply of plants, 84. evaporation, rate of, 88. makes food available for plants, 84. Soil temperatures, 78. affected by sunshine, 95. annual ranges, 80. as affected by soil cover, 80. snow cover, 80. desirability of temperature rec- ords, 80. diurnal changes in, 79. lag proportional to depth, 79. effect on tobacco root-rot, 251. flax-wilt, 2.54, 255. grain smut, 254. loss of heat, 79. most favorable temperature, 79. Soil temperatures — Continued snow-cover, 80. source of heat, 79. Solar climate, 61. Solar energy, 94. Sorghums, 181. water requirements of, 89, 90, 93. Sorgo, 243. Soybeans, 219. Spinach, 219. Spraying forecasts, 260. Spring wheat, belt, 102, 184. growing period, 191. in the United States, 183, 184. as affected by temperature, 183. as affected by moisture, 183. rain, 192-199. seed, 252. seeding and harvesting, 185-187. temperature, 194, 190, 199. zero of vital temperature, 68. Squashes, 216. Strawberries, 135, 136. adaptation to climate, 135. critical temperatures, 139. effect of sunshine, 96. when harvested, 135. Sugar-beets, 244-247. sugar content affected by tem- perature, 244-246. Sugar-cane, 243, 244. water requirements of, 243. Sugar products, 243-248. honey, 247, 248. maple sugar and sirup, 247. sugar-beets, 244-247. sugar-cane, 243, 244. Sun scald, 96, 133, 134, 234. Summation processes, 68 73. Sunshine, alfalfa, 240. apples, 96. beans on California coast, 96, 97, 217. corn, 173. cotton. 111. (See cotton.) effect on plants, 95. effect on temperature of plants, 74, 75, 95. grapes, 132. 302 INDEX Sunshine — Continued -hour degree, 94. variation with latitude, 94. important meteorological factor, 93, 94. intensity of, varies with latitude, 94. sometimes unfavorable, 95, 96. sugar-beets, 246. vegetables, 215, 216, 219. Sweet potatoes, 216. Temperate belts, 63. Temperate zones, 63. Temperature, adiabatic change in, 6. annual range, 6. greatest over land, 6, 61. at which growth begins, 67. cold waves, 16, 274. diurnal range, 5. greatest over land, 5, 61. slight in cloudy weather, 5. effective temperatures, 67. for growth, maximum, optimum, minimum, 70. highest in early afternoon, 5, 281. inversion of, 4, 276. limits agriculture, 63. limits crop areas, 64. lowest just before sunrise, 5, 281. maximum and minimum, 8, 281. most important in climate, 64. of climatic zones, 63. plants, 74-77, 95. soil, 78. (See soil temperatures.) sun the source of heat, 4. three summation processes, 68, 69. vertical gradient, 7. warm waves, 18. Temperature, in relation to, alfalfa, 239, 240. almonds, 126, 139. apples, 126, 139. apricots, 129, 139. barley, 64, 142. bitter-rot of apples, 128, 129. blooming of timothy, 242. boll weevil, 122, 123. buckwheat, 143, 144. germination of, 144. Temperature, in relation to — Cont. cattle-tick, 256. cherries, 139. chinch-bugs, 255. clover, 241, 242. codling moth, 129. corn, 145. (See corn.) cotton, 109. (See cotton.) cranberries, 130, 139. critical for fruit, 138-140. cutworms, 255. dates, 131. flax, 124. (See flax.) germination, buckwheat, 144. corn, 149. spring wheat, 194, 196, 199. ginning cotton. 111, 112. grain sorghums, 181. grapes, 131, 132, 139. grasshoppers, 255. hay, 238, 239. hemp, 125. hessian fly, 256. honey, 247, 248. insect damage, 255, 256. parasites of, 256. liberation of carbon dioxide, 76. maple products, 247. millet, 242. oats, 64, 173, 175. (See oats.) olives, 133. oranges, 137, 139. peaches, 134, 139, 140. plant diseases, 233, 236, 253, 255. plant distribution, 64. planting dates, 67, 68, 147, 173, 222. pollination of fruit, 140. potatoes, 222. (See potatoes.) rice, 179. rye, 180, 181. seeds, 251, 252. strawberries, 135, 139. sugar-beets, 244-247. sugar-cane, 243, 244. timothy, 242. tobacco, 248-251. vegetables, 215-219. vegetation, 4, 8, 64. wheat, 183. (See wheat.) white-grub, 256. INDEX 303 Thermal belts, 62. Thermal constants, 67-69, 161, 162, 164, 165. Thermometers, 7. Thunder-storms, 283. nature of lightning, 284. Timothy, 242. Tobacco, 248-251. bed-rot, 250. in the United States, 248. root-rot, 251. under shade, 249. Tomatoes, 96, 97, 216. Torches, 278. Tornadoes, 16, 17. shooting tornadoes, 15. tornado tubes, 17. where they occur, 17. Torrid zone, 63. Total effective temperatures, 68. summation process, 68. Lissner's law, 77. plant development depends on a constant aliquot, 77, 78. plant temperature should be considered, 74. solution possible, 77. three methods, 68-72. varies with other conditions, 78. value of, 77. weakness of, 73. Transpiration, and drought, 172. compared with evaporation, 85. defined, 85. from corn, 85, 150, 172. influenced by weather, 85. maximum, 85. promoted by sunshine, 96. Tropical belt, 63. Turnips, 219. Unknown coefficients, 46, 50. van't Hoff law, 69, 7'?. Vegetables, 215-221. planting dates, 219, 220. Vegetation (native) a key to farm operations and field crops, 28-30. Vegetative periods, 271-273. Velvet beans, 219. Verdant zones, 62. Vital temperature, zero of, 67, 68. Warm-season crops, 106, 107, 215, 216. Warnings, special, cold wave, 265. flood, 264, 265. frost, 265. snow, 265. stock, 265. storm, 264. Water content of soils, 85. Water requirements of plants, 88, 89-93, 150, 151, 237, 238. amounts for different plants, 89- 93, 183. Watermelons, 216. Waterspouts, 16. Water-vapor, 2, 8, 9, 10, 266. Weather, defined, 1. Weather and crops, 106. factors must be in proper propor- tion, 23. Weather and seed, 252. Weather-cotton equation, 113-115. Weather forecasts, 259. frost, 270, 274, 275. laws, 261, 262. local, 260, 261. local weather signs, 265-267. long-range, 268. observations for, 261. pressure variations principal fac- tor, 264. shippers of perishable products, 259, 260. special, 260. alfalfa cutting, 240, 260. alfalfa seed, 240. raisin-drying, 260. sheep shearing and lambing, 26C. spraying, 260. special warnings, 264, 265. weather maps, 261. Weather maps, 261, 274, 275. Weather risk, 104. 304 INDEX Wheat, 181-212. Australia, in, 211, 212. belt, 101, 181, 182. critical period, 191, 212. composition of, 185. distribution and rainfall, 183. England, in, 212, 213. fruiting period, 188. growth period, 186, 188, 191. harvesting, 185-189. hessian fly, 186, 189, 211. Italy, in, 212. northern limit, 63, ISl. rainfall, and, 191-212. rust, 185, 211. seeding, 185, 186, 189. soil temperatures, 183. to escape hessian fly, 186, 189. United States, in the, 182-184. White-grub, 256. Wilting coefficient, defined, 85. varies in different soils, 85. Wind, 15. an important climatic factor, 97. bacteria, 254. beneficial or damaging, 97, 98. blizzards, 18. chinooks, 19. cold waves, 16. depends upon the pressure, 262, 266, 267. doldrums, 15. estimating the velocity, 20. flax, 124. Foehn, 19. hot winds, 19. how measured, 19. insect damage, 255. land and sea breezes, 16. Wind — Continued monsoon winds, 16. mountain and valley winds, 16. pressure exerted by, 20. spread of boll weevil, 123. surface currents, 15. interruption of, 15. trade winds, 15. tornadoes, 16, 17. warm waves, 18. what makes it blow, 15. Winter wheat, belt, 101, 182. growing period, 188, 191. hessian fly, 186, 189, 211. in the United States, 181, 183. as affected by moisture, 183. as affected by temperature, 183. rainfall, 199, 200, 203-207. rust, 185, 191. seed, 252. seeding and harvesting, 185, 188, 189. to escape damage by hessian fly, 189. snow-cover, 202. snowfall, 202, 203. temperature, 199-207. winter-killing, 208, 209. zero of vital temperature, 68. Winter-kilHng of wheat, 208, 209. Winter oats, 175. Wood fires, 279, 280. Zero of effective temperature, 67, 68. Zero of vital temperature, 67, 68. a new zero suggested, 67, 68. for most crops, 68. Zones, climatic, 63. I*rinted in the United States of America