U. S. DEPARTMENT OF AGRICULTURE. q k. Gilbert. CONDITIONS IN SOILS OF THE ARID REGION. HY MILTON WHITNEY, Chief of the Division of Agricultural Soils. [Reprinted froen the Yearbook of the U. S. Department of Agriculture for 1894.] WASHINGTON: GOVERNMENT PRINTING OFFICE. 1-895. U. S. DEPARTMENT OF AGRICULTURE. CONDITIONS IN SOILS OF THE ARID REGION. r^ BY MILTON WHITNEY, Chief of the Division of Agricultural Soils. [Reprinted from the Yearbook of the U. S. Department of Agrisulture for 1894.] WASHINGTON: GOVERNMENT PRINTING OFFICE. 1895. 33 — < ,'**•* .-r 32 \" 31 t 1 30 / / 29 y 28 , / ' 27 / 26 * 25 f ' i 24 • 1 \ 23 1 1 \ 22 f 1 I / \ 21 4 i \ 1 \ 20 i f \ / \ 19 I \l \ 18 / y \ 17 I 16 1 15 / 14 ¥ 13 12 1887 1890 1881 1886 1892 1891 1888 1880 1885 1879 1882 1878 1889 1877 1883 1884 Pig. 11. — Average yield, of corn in bushels per acre in Kansas, 16 years. The fact remains, however, that in years of normal rainfall well dis- tributed over the growing season, small though it is, a good crop is obtained throughout the semiarid region, and even on the so-called arid plains, where the land is properly cultivated. Statistics compiled by tbe Kansas board of agriculture show that in the sixteen years from 1877 to 1892, inclusive, the yield of corn per acre in the State of Kansas exceeded 30 bushels in eight seasons and the yield fell below 20 bushels per acre in three seasons. This is shown graphically in the accompany- ing illustration (fig. 11). RELATION OF SOILS TO CROP PRODUCTION. 159 The average yield of wheat during this same period exceeded 15 bushels per acre during seven seasons and was under 11 bushels per acre five seasons. In the arid portion of the State a fairly good season occurs about two years in five, the remaining three out of the five seasons being too dry for a good crop. The fact that they can make a crop at all with an annual rainfall of 20 inches under the conditions which have already been considered is surprising, and indicates that there must be conditions which are not strictly comparable with those in the humid region, and that there are advantages to counteract the apparently unfavorable conditions. DEPTH OF SOIL MOISTURE. A considerable portion of the 2 inches of annual rainfall of the arid region which finds its way into streams and rivers must flow off over the surface and not even enter the soil. The extreme and rapid varia- tion in the volume of the rivers, and the frequent torrential showers, during which the ground is flooded with water, indicate that this con- dition does in fact prevail to a large extent. Some water is retained by local depressions until it sinks, and there are undoubtedly soils of loose, light texture into which a considerable amount descends and finds its way to the rivers and streams by slow percolation; but as a rule there seems to be no connection between the surface moisture and the underlying " water table." The natural prairie sod sheds water like a roof when it is delivered rapidly and in large volume, and it is only with a long continued, gentle rain that the soil and subsoil under the sod will absorb any considerable amount of moisture. During a recent examination of the conditions in the soils of the plains of western Kansas, Nebraska, and eastern Colorado, no trace of moisture was found in a number of borings from just below the surface to a depth of 3 feet under the natural prairie sod, except on the light soils of the sand hills near Garden City and in a few depressions, where water had evidently been caught. The season had been exceptionally dry, but an inch of rain had fallen about a week before the examina- tions were made. Where the sod had been broken and the land had been under cultivation during the season the subsoil was quite moist, and more moist the more thorough the cultivation had been. At Geneva, Kebr., the soil and subsoil immediately under the prairie sod was so dry that it was extremely difficult to take a sample with an auger, both because it was hard to bore into and because the material loosened by the auger was so dry and powdery that it ran off the auger like fine, dry dust or sand. In an oat field, which had been thoroughly prepared by subsoiliug two years before, the subsoil was quite moist, although the ground had not been actually cultivated for a year. In an adjacent field which had been subsoiled the previous year, and dur- ing the present year had been thoroughly cultivated in nursery stock, the subsoil down to a depth of 3 feet was so moist that it could be 160 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. molded in the hand. These three localities were not over a few hun- dred feet apart and had been exposed to precisely the same rainfall, but had been subjected to these different methods of cultivation. It is a common inquiry in the arid region after a rain, how far the moisture has descended, or, generally, how far it is down to dry soil. The evidence of well-diggers is that after passing, through the upper few feet of earth the underlying material is dry until they approach the water-bearing layers of sand and gravel. The fact of the accumu- lation of alkalies shows that the subsoil is not continuously wet down to the "water table," as otherwise these would be leached out and car- ried off through the subsoil as they are formed. Water descends very slowly and to a very limited extent in a per- fectly dry soil, while it will spread out very rapidly in a soil which is already moist, but short of actual saturation. Water may fall for days upon a pile of dry manure and not wet the mass deeper than a few inches. Water may likewise fall upon a dry dust pile and not spread through the mass, but be contained near the surface, unless it continues to fall, in which case the whole mass of the dusty material may become saturated. Water does not readily spread through a previously dry soil, because the tension or contracting power of the surface of the water is greater than the attraction of the soil grains, which tends to cause its diffusion through the mass. One may see, therefore, a nearly saturated layer closely adjacent to a perfectly dry and dusty mass. On the other hand, if there is any appreciable amount of moisture in tbe soil the tension of the water surface will cause it to contract and pull water from above into the subsoil. It would follow, therefore, that the moisture would not descend into the dry subsoil of the upland prairie until the successive depths had become so far saturated that they could no longer hold the water back, and it would pass downward very gradually into the lower depths sat- urating, or nearly saturating, each successive depth as it progressed. Unless the rainfall was so great and so continuous as to saturate the soil to a considerable depth, the water would not pass down to a great extent in the dry material. The whole supply of moisture absorbed by the soil would remain within a short distance of the surface, and when evaporation was started again from the surface or the moisture was used up by plants the water would be pulled up again from the depths to which it had progressed rather than proceed on its downward course. There is less force to pull it down into the dry subsoil than its own con- tracting power, which pulls it up through the moist soil to the plant or to the surface of the ground. It appears probable, therefore, that in the more retentive soils of the arid regions the whole of the 20 inches of rainfall, or as much of this as is absorbed by the soil, will be held within a few feet of the surface, within easy reach of the roots of plants. The problem should be how to conserve the moisture, diminish the evaporation from the RELATION OF SOILS TO CROP PRODUCTION. 161 soil, and maintain as much as possible of the supply for the use of crops. Two things suggest themselves at once: The preparation of the soil must be sufficiently thorough and deep to insure the absorption of the whole amount of the rainfall, and preparation should be so thorough and deep that this water will be carried to a sufficient depth to dimin- ish the chances of surface evaporation and prevent the saturation of the upper soil, which would be prejudicial to plant growth. The water must be absorbed as deeply as possible, so as to check surface evapo- ration, and at the same time be maintained sufficiently near the surface to be available to plants as needed. Where water is of so much value and of such vital importance, not a drop of rainfall should be allowed to waste by flowing off over the surface. It should all be absorbed by the soil. The rains are often so torrential in character that the soil must be in a condition to absorb the water very rapidly to prevent any loss. The conditions actually existing in these soils should be made the subject of careful and thorough investigation. The amount of mois- ture actually maintained by the soils should be ascertained by daily determinations, to give a basis for working out improved methods of cultivation or planting for the conservation of moisture. The rainfall should be followed and its whole history worked out from the time it enters the soil. In the first place, how deep does the rainfall penetrate into the different soils of the plains? This could be ascertained at different depths at intervals of a week or ten days throughout the sea- son by moisture determinations. Is any of the rainfall drawn so low as to be unavailable to plants and lost by percolation into the "water table"? How much of the rainfall evaporates from the different types of soils, how rapid is this evaporation, and how even are the condi- tions which the principal soils maintain? What part of the moisture evaporates from the soil and what part is transpired by the growing crop? How much water does a plant transpire in the arid regions for every pound of dry matter produced as compared with the same class of crops in the humid regions? These are all fundamental questions, which will have to be understood in order to secure any intelligent improvement of the methods of cultivation and cropping. More than half of the annual precipitation in Kansas occurs in the four crop-growing months of April, May, June, and July. During May and June especially the frequent showers induce a very rank and lux- uriant growth, and there is nearly always up to the middle or end of June the prospect of a large corn crop. It is not uncommon, however, for a dry spell in July to reduce the promised yield by 100,000,000 or 150,000,000 bushels. These dry spells last from two to four weeks, frequently resulting in great damage to the corn crop. Wheat is usually harvested before this midsummer drought comes on, and there is less variation in the yield of wheat in the State than in 162 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. the corn crop. Such crops also as turnips, millet, and sorghum do very- well from the August rains. The drought comes frequently at the most critical time of all in the development of the corn plant— just as it is tasseling out. It should be possible to breed new varieties, maturing earlier or later, so as to secure a crop at a different stage of develop- ment during this usual summer drought. HOT WINDS. The very time when the crop is suffering from drought is the time of all others when hot winds are liable to occur. These winds blow at the rate of 20 to 30 miles per hour, the temperature of the air frequently ranging from 100° to 106°, with only 20 to 30 per cent of relative humidity. This vast body of dry, hot air passing over the crop induces such rapid evaporation that the roots can not possibly supply sufficient moisture, and the plants are completely desiccated, or dried out. The cells dry up to such an extent that they die, and the whole leaf struc- ture collapses and hangs limp and lifeless. The effect of hot winds upon the crop is markedly different from the effect of drought alone. In an ordinary drought the fodder dries and is cured much as if it had been cut and exposed to the sun and air, the plants, however, remain- ing erect. The effect of hot winds is much more quickly fatal to the crop; two or three days is often sufficient to destroy the most promis- ing field of corn. The evaporation from the plants under these condi- tions must be enormous. It is so excessive, indeed, that even with the soil quite moist the powers of the plant may be taxed beyond endurance. There are several possible ways to prevent or greatly lessen the injury from hot winds. Wind-breaks diminish the injurious effects of hot winds, for when the air is quiet the evaporation from the leaves increases the humidity of the air immediately around them, and this diminishes the evaporation from the leaf. If this air is removed, however, and quan- tities of dry air are rapidly presented to the plant the excessive evapo- ration is continued. Anything, therefore, which will retard the rate of movement of the wind will tend to diminish evaporation from the plants within the area of its influence. The more moist the soil can be kept through methods of cultivation the less damage there will be to vege- tation, for the roots will have a larger supply of moisture to draw from. The hot winds rarely do much damage over irrigated fields when the water supply can be properly controlled. The most disastrous effect of hot winds, however, frequently follow a rainfall occurring after a long period of drought. During the rain transpiration from the plant is checked and the cells become excessively turgid and possibly weak- ened through distention aud possibly by the presence of organic acids. When the hot winds immediately follow this abnormal condition of the plant, the evaporation is rapidly increased, the cells lose their water and collapse and die, as possibly they would not have done if the conditions preceding the hot winds had been more normal. ADVANTAGE OF SOILS TO CROP PRODUCTION. 163 BENEFIT OF UNDERSTANDING SOIL CONDITIONS. It may be asked what advantage it would be to understand soil con- ditions and what control of them is possible. As regards the first question, this knowledge will make it possible intelligently to classify the soils according to the conditions which they maintain and predict what classes of crops they will prove adapted to grow. It would sug- gest also the way in which the soil conditions should be changed to make them correspond still more closely to the requirements of the class of crops to which they are most nearly adapted. As regards the second question, it is quite possible, through intelligent methods of cultivation, of cropping, and of fertilization, to change the conditions maintained by soils by changing their physical texture. It is likewise possible that we shall be able in time to control the amount of water taken up from a soil and transpired by plants. In a soil containing much water it should be possible to prevent the plant taking an excessive amount, thus checking the too luxuriant growth of vegeta- tion, or in a soil containing a small amount of moisture to induce the plant to take up more water than it otherwise would. This control will come through the effect of fertilizers and chemicals upon the roots which will stimulate or diminish the transpiration powers of the plant. SUBSOILING. Where the amount of rainfall is so small it is obviously important that the soil should absorb all of the rain which falls upon it. It is folly to allow water to flow off the farm, incidentally causing damage by washing, and then spend large sums to put in irrigation ditches to replace it by water which others have allowed to flow off their land. Wherever a drop of water flows off the field it is an indication that the soil is not in a proper physical condition. Where this occurs in a dry soil the main preparation of the land should be as deep as possible, so that the water may be carried down and thus diminish the rapidity of the evaporation and loss from the surface. If deep plowing will not accomplish this object, subsoiling will be found invaluable in open- ing up the close and compact subsoil. A subsoil plow should be as small and light in all its parts as is consistent with the great resistance it has to encounter. The point should be small and narrow, like the point of a pick, somewhat larger at the back than at the front. It is not necessary to have this large, for any implement which could be pulled through the subsoil would break and loosen it sufficiently to change its physical texture. There are some soils where subsoiling would not only be of no advantage, but in which it might be a positive injury to the land. A light, sandy soil having already an open and porous subsoil would not be benefited by having this subsoil made still more open. A farmer should judge whether subsoiling is advisable by the character and condition of the subsoil, and particularly witli a view to the question whether any part of the rainfall flows off the surface. 164 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. The conditions in the arid regions are so different from those in the humid portion of the country that the methods adapted to the former are not necessarily well adapted to the latter. The act of subsoiling, the breaking up and stirring the soil to a depth of 12 or 15 inches, tends to dry it out; and unless a rain follows before a crop is put in the subsoiling may work positive injury to the first crop, although the beneficial effects would be felt in the succeeding crops. To secure benefit the first season the subsoiling must be done a considerable length of time before the crop is put in, in the hope of receiving heavy and long-continued rains. It is obvious that the nature of-the soil itself will largely determine the depth to which the cultivation should be extended, and the character of the season should determine at what time this cultivation should take place. It is very necessary in this deep cultivation of the soils of the arid regions that care be taken not to turn under a heavy sod or a quantity of organic matter, especially when the season or the soil is dry. In these dry soils a heavy sod or a lot of trash or stubble will not readily decay when turned under; indeed, it may remain undecayed for several years. In this condition it will break off capillary connection with the subsoil, so that if the crop is planted on the upturned sod it may actually perish for lack of moisture. It is a very common experience, nevertheless, with farmers on the plains that where the sod is broken very shallow, so shallow that the crop roots below it, the upturned sod acts as a very efficient mulch to prevent evaporation, and so increases the yield of crops. After a soil is once deeply prepared, the after cultivation of the crop should be as shallow as possible in order to maintain a mulch of loose, dry soil over the surface to check evaporation, yet to keep this mulch as thin as possible so as not to dry out more of the soil than is abso- lutely necessary. While cultivation should thus be very superficial, it should be frequent and continued well into the fruiting period of the crop. The old rule of giving one cultivation after each rain is not sufficient. Thorough preparation of the land, with subsoiling where this is nec- essary to break up a compact subsoil, followed by shallow but frequent cultivation of the surface, will undoubtedly make the crop much safer and surer in the arid and semiarid regions of the West. r^