THE CARBON DIOXIDE OF THE SOIL AIR A THESIS PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF CORNELL UNIVERSITY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY BY HAROLD WORTHINGTON TURPIN SEPTEMBER, 1918 Reprinted from Memoir 32, AprU, 1920, of Cornell University Agricultural Experi- ment Station. THE CARBON DIOXIDE OF THE SOIL AIR A THESIS PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF CORNELL UNIVERSITY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY BY HAROLD WORTHINGTON TURPIN SEPTEMBER, 1918 Reprinted from Memoir 32. April, 1 920. of Cornell University Agricultural Experi- ment Station. LIBRARY Or CONGRESS MAR 261921 DOCUMENTiJ uiV.siON CONTENTS PAGE Historical review 319 Importance of tlie carbon dioxide in the soil 319 Factors aiifecting the amount of carbon dioxide in the soil air ... . 321 Soil organisms 321 Soil conditions 321 Seasonal conditions ! 321 The crop 322 Chemical factors 323 Simimary 323 Experimental work 324 Experiment 1 324 Results 328 Effect of crop 328 Carbon-dioxide and water relationships 331 Effect of temperature and atmospheric pressure ....... 335 Summary of experiment 1 337 Experiment 2 337 Results ; 339 Summary of experiment 2 344 Experunent 3 344 Results 345 Simimary of experiment 3 347 General summary 347 Bibliography 349 Appendix (containing tables) 353 315 Digitized by the Internet Archive in 2010 with funding from The Library of Congress http://www.archive.org/details/carbondioxideofsOOturp THE CARBON DIOXIDE OF THE SOIL AIR THE CARBON DIOXIDE OF THE SOIL AIR H. W. TURPIN Carbonic acid has long been recognized as an important soil solvent. On this point, at least, authorities are well agreed, but from the data available it is not yet clear what factors are most important in controlling the production of carbon dioxide in the soil. It is generally conceded, however, that a large proportion of the carbon dioxide found is due to soil microorganisms. The significance of plant roots in this connection has been recognized by some investigators, while others appear to be not quite decided as to how important plant-root excretions are. HISTORICAL REVIEW IMPORTANCE OF THE CARBON DIOXIDE IN THE SOIL That carbon dioxide in solution is an important soil solvent has been shown by Stoklasa and Ernest (1909).^ These workers point out that when ground gneiss and basalt are mixed with nutrient solutions, the amount of phosphorus and potassium absorbed by the plants grown is directly proportional to the carbon dioxide produced per gram of dry matter of the roots. Aberson (1910) concluded, as a result of studies with young plants, that, while the excretions from plant roots may not be sufficiently concentrated (in carbon dioxide) to have a marked effect in dissolving insoluble materials, still the mucilaginous covering of the root hairs, containing a saturated solution of carbon dioxide, is entirely sufficient to bring into solution the insoluble soil constituents with which it comes in contact, especially the phosphates. The limited usefulness, as a solvent, of the carbon dioxide secreted by plant roots is pointed out by Pfeiffer and Blanck (1912), who show that in soils treated with phosphates the carbon dioxide given off by plant roots is not a sufficient solvent to account for all the mineral nutrients obtained by the plant from the soil. 1 Data in parenthesis refer to Bibliography, page 349. 319 320 PI. W. TuEpm Bssides its importance as a direct solvent in the soil, carbon dioxide has considerable significance as an indicator of certain soil activities Hutchinson (1912) observed a relationship between the biological activi- ties and the amount of carbon dioxide in the soil. Russell (1915, a and b) noticed a close parallehsm between the carbon-dioxide and the nitrate production in the soil, there being more of these constituents in spring and fall than in midsummer and winter. It was pointed out later by Russell and Appleyard (1915) that the curves for the bacterial numbers the nitrate production, and the carbon-dioxide content in the soil thru- out the season, show marked simHarity, indicating that the carbon dioxide may serve to some extent as an indicator of other soil activities. NeUer (1918), however, could find in his experiments no correlation between the ammonia production and the carbon dioxide formed, except in cases in which he used pure cultures of bacteria. The lack of correlation he attributed to the predominating influence of fungi in the soil. _ In addition to its importance as a direct solvent in the soil and as an indicator of certain soil activities, carbonic acid may possibly be significant as an inhibitor of the activity of soil organisms and perhaps even of plant growth. Large quantities of carbon dioxide in the air have been found by numerous investigators to be detrimental to the growth of the higher plants. E. Wollny (1897) observed an increased production of carbon dioxide with an increase in the organic matter in the soil, but the increase to the umt of organic matter was less with the larger appHcation. This Wolhiy attributed to the inhibiting effect of carbon dioxide on the bacterial activities. The work of Plummer (191G), however, showed that exceed- ingly large amounts of carbon dioxide do not interfere with the activities of the ammonifying and nitrifying organisms, provided, in the latter case that the oxygen supply is not reduced below a certain minimmn The same investigator showed that the maximum carbon-dioxide production m the soil corresponds with the point of maximum nitrification In studies on the carbon dioxide produced in lysimeter tanks, Bizzell and Lyon (1918) noted a marked decrease in the production of this gas after the blooming period of an oat crop on Dunkirk clay loam. This decrease they say, "was apparently due to the depressing effect of the crop on production by bacterial action." Such a decrease was not found to take place on a Volusia silt loam. The Carbon Dioxide of the Soil Air 321 FACTORS affecting THE AMOUNT OF CARBON DIOXIDE IN THE SOIL AIK Soil organisms Most investigators consider that soil organisms play a large part in the production of carbon dioxide in the soil. Pettenkofer (1858, 1871, 1873, 1875) concluded, as a result of his investigations, that most of the carbon dioxide in the soil is due to living organisms. Later, E. Wollny (1880b) found that there is only a small production of carbon dioxide in an atmosphere of hydrogen gas, while cliloroform ahnost completely stops the power of the soil to form carbon dioxide. He concluded that carbon dioxide is produced largely by bacteria. Further confirmation of this is to be found in the studies of Deh^rain and Demoussy (1896), which showed that sterile soil at a temperature of 22° C. produces only insignificant amounts of carbon dioxide. Stoklasa and Ernest (1905), after working with beets, clover, oats, and other plants, noted that a bare soil produced, in one hundred and fifty days, more than twice the carbon dioxide produced by a crop of wheat on the same area in sixty days. They observed also a correlation between the numbers of bacteria and the carbon dioxide produced at different depths in the soil. Hutchinson (1912) concluded that carbon-dioxide production is a reliable measure of bacterial activity. Soil conditions Where soil conditions are favorable to the action of bacteria, the carbon- dioxide content is usually high. For example, Stoklasa (1911) obtained the greatest production of this gas in a soil that was well aerated, sHghtly alkaUne, and well suppKed with readily available plant nutrients. This was found by E. Wollny (1897), Russell and Appleyard (1915), and others, to be especially true in the case of soils having readily available organic matter. Very small amounts of carbon dioxide were found in the swamp rice lands of India by Harrison and Aiyer (1913), showing that unfavorable soil conditions are associated with a low content of carbon dioxide. Seasonal conditions Russell and Appleyard (1915, 1917) emphasized the importance of seasonal conditions on the carbon-dioxide content of the soil. In their investigations they observed that a rise of temperature is accompanied 322 H. W. TuEPiN by an increase in carbon dioxide. Tlie same fact had been previously noted by MoUer (quoted by E. WoUny, 1880 a), by Deherain and Demoussy (1896), by Stoklasa and Ernest (1905), and by Leather (1915), and was later mentioned by Potter and Snyder (1916). Carbon-dioxide production was found by the Rothamsted investigators (Russell and Appleyard, 1917) to be correlated ^^dth moisture and rain- fall. Previously E. Wollny (1880a) had observed that increasing amounts of water up to 9 per cent, in a quartz sand mixed with peat, resuhed in an mcrease in the carbon dioxide. Deheram and Demoussy (1896) found that there was an optimum water content for carbon-dioxide production in a garden soil. Van Suchtelen (1910) found the greatest amount of carbon dioxide when the soil with which he worked was 75 per cent saturated with water. The relationship observed by RusseU and Appleyard (1917) between the ramfaU of the preceding week and the carbon-dioxide content of the soil, was believed by them to be due largely to the oxygen dissolved in the ram water. That this may be true is shown by the earher work of E. WoUny (1897), and also by that of Fodor (1875), who showed that there is a relationship between the- carbon-dioxide content and the oxygen of the soil, mdicatmg that the carbon dioxide is probably produced by oxidation processes. ■ The crop The evidence available thus seems to point to bacteria as the chief source of soil carbon-dioxide. There are some data, however, which show that plants may play a considerable part m the production of this gas in the soil. Stoklasa and Ernest (1909) and Aberson (1910) noted that the roots of plants excrete large amounts of carbon dioxide. That the gas so formed IS not msignificant is proved by the fact that field studies conducted at Rothamsted by Russell and Appleyard (1917) showed a considerably higher content of carbon dioxide in cropped soil than appeared in the bare soil, this being especially marked in May, at the trnie of the most active growth of the plant, and at the time of ripening. The same condi- tion was observed by Bizzell and Lyon (1918) in the case of an oat crop on Uunlark clay loam, where the greatest production of carbon dioxide took place at about the time of blooming. Potter and Snyder (1916) observed The Cahbon Dioxide of the Soil Air 323 similar results with timothy, but they were unable to decide whether or not this increase of carbon dioxide was due to the plant-root excretions or to the decay of root particles that had died during the growth of the crop. The work of Stoklasa and Ernest (1905) showed that the younger the plant is, the greater is the amount of carbon dioxide formed. Kosso- witch (1904) noted that mustard grown in quartz sand and nutrient solutions produced an increased amount of carbon dioxide up to the time of blooming. This was observed also by Barakov (1910) in the case of plants growing in lysimeters. That different lands of plants produce different amounts of carbon dioxide has been shown by Lau (1906), who found that potatoes and legumes give off more carbon dioxide than do other crops. Red clover, beets {Beta vulgaris), and oats were found by Stoklasa and Ernest (1905) to produce more carbon dioxide than other plants, and in the order named. Russell and Appleyard (1915), however, could find no difference in the carbon-dioxide content of soils on which different species of plants were growing. Chemical factors From the brief survey given, it would seem correct to say that most of the carbon dioxide found in the soil is the result of biological activity. There is some evidence, however, showing that chemical action may play a small part. E. Wollny (1880 b) noted a very slight production of carbon dioxide in soil treated with chloroform. The same investigator demon- strated later (E. Wollny, 1897) that organic matter in the absence of oxygen reduces manganese and iron oxides and forms carbon dioxide. Very little carbon-dioxide production in sterihzed soil kept at a temperature of 22° C. was observed by Deh^rain and Demoussy (1896). They found, however, a very considerable production of carbon dioxide in soil heated to 90° C. and above. An oxidizing enzyme in the excretions of the root hairs was considered by MoUsch (1888) to be capable of producing carbon dioxide from organic substances. It is probable that carbon dioxide produced by chemical means forms an extremely small part of the total carbon dioxide found in the soil. Summary In this review of the literature of the subject, certain facts stand out. Authorities are agreed that bacteria play an unportant part, probably 324 H. W. TuRPiN the most important part of all the factors concerned, in the production of carbon dioxide in the soil. Climatic factors, such as temperature, rainfall, and air supply, have a marked effect on the carbon-dioxide content of the soil. Crops increase the amount of carbon dioxide in the soil, either by direct excretions from the roots or thru the decay of root particles from the growing crop. Finally, the nature of the soil itseK causes marked differences in the production of carbon dioxide. The results reported in this paper confirm some of the above con- clusions, but they also show that the influence of the crop has been under- emphasized. EXPERIMENTAL WORK In the author's first experiment, a study was made for two seasons (1917 and 1918) in the greenhouse, with soil cropped to oats and with uncropped soil. The object was to try to establish some definite relation- ship between the carbon dioxide in a cropped soil and that in an uncropped' soil, where the crop itself introduced the only variable. Such a relationship having been established, it was decided to determine in the second experiment whether or not it would hold for a different crop. The third experiment was designed to analyze the factors concerned in the production of carbon dioxide, and, if possible, to assign to each its respective part. EXPERIMENT 1 The cylinders illustrated in figure 44 were used in the first experiment. These cyUnders, eight in number, were made of galvanized iron, coated inside with a layer of paint to insure their being air-tight at the joints and to prevent rusting. They were 3 feet high by 1 foot in diameter, and each had a cone-shaped bottom leading to the cocks on the outside as indicated in figure 45. The cone-shaped bottom was filled with gravel, above which was placed a 12-inch layer of soil from the second foot of the field soil. Above this was placed a foot of surface soil. The soil used was Dunkirk clay loam. The moisture in the soil was maintained thruout the course of the experiment at 30 per cent on the oven-dry basis. The soil was covered with a half-inch layer of quartz sand in order to reduce the evaporation, the sand being added to the cropped soil immediately after seeding. The dry weight of the soil in each of the cans was 94.3 pounds. The Carbon Dioxide of the Soil Air 325 -' ■ .# Fig. 44. c.^ns used ix first experiment The four cans at the left contain an oat crop, which is shown at the period of its growth a montii before the maximum amount.,of carbon dioxide was found in the air of the cropped soil Fig. 45. arrangement of cylinder, sampling flasks , and aspirator 323 H. W. TuRPiN Before seeding, some preliminary studies were made in order to ascertain the best method of obtaining the sample of soil air for analysis. It seemed impracticable to use any method other than one that could be carried out rapidly, since it was planned to run the test for two seasons and to take the samples twice each week thruout the year. As a result of the preliminary studies, it was found that by aspirating four Hters of air thru the soil cans in five minutes, and passing the air thru two graduated 500-cubic-centimeter Erlenmeyer flasks, samples could be obtained in the two flasks which checked with each other, indicating that the air originally present in the flasks had been replaced by a representative sample of the air in the soil. If more or less than four liters was aspirated thru the soil, the amounts of carbon dioxide in the two flasks did not check, indi- cating, in the first case, that the original air in the soil had been replaced by air from the atmosphere and that some of the latter was passing into the flasks, and in the second case that the original air in the flasks had not been completely replaced in the flask nearer the aspirator. The method of sampUng is shown in figure 45. After the aspiration was completed, the cocks on the flasks were closed and the flasks were removed to the headhouse, where they were allowed to reach room temperature. The excess pressure in the flasks was reUeved by opening one of the cocks for a moment. The temperature was noted at this point, as all calculations were reduced to per cent by volume of carbon dioxide at standard atmospheric conditions, that is, 760 milhmeters pressure and 0° C. Excess of standard barium hydroxide was next run into the flasks. The volume of the barimn hydroxide added was noted, and .was sub- tracted from the total volume of the flask. The cocks were then closed, and the flasks were allowed to stand, with occasional vigorous shaking, for about thirty minutes, after which the excess barium hydroxide was determined by titrating with standard oxalic acid whose equivalent in terms of carbon dioxide had been previously determined by titrating with standard potassium permanganate solution. The method of aspirating air thru the soil has been criticized by Pot- ter and Snyder (1916) in a paper describing experiments in which they determined the carbon dioxide evolved by drawing, a current of air continuously over the soil surface. They maintain that the occasional drawing of air thru the soil will result in a temporary decrease in the content of carbon dioxide, which, however, will soon be restored by the The Carbon Dioxide op the Soil Am 327 activities of the soil, and tliis accumulation of carbon dioxide will, by the mass action law, finally result in a retardation of further production of the gas. On the other hand, they maintain that by drawing a current of air continuously over the surface of the soil, conditions more nearly similar to those obtaining in the field will result. This may be true for experiments conducted in a quiet room; but in the greenhouse, where there is a circulation of air, there is ample opportunity for diffusion to take place from the soil, especially where, as in these experiments, one of the lower cocks of the soil can was always left open, so that a sample taken at any particular tune should be truly representative of the carbon dioxide actually present under normal conditions. It has been pointed out by Leather (1915) that usually only about 25 per cent of the carbon dioxide in the soil is in the gaseous state, the remainder being dissolved in water. It is reasonable to suppose that, once the soil water is saturated with this gas, any further production of carbon dioxide will tend to increase the content in the soil air. Considering these facts, then, it will be seen that the method used in these tests will not give, and was not intendedto give, absolute amounts of carbon dioxide; but it nevertheless should yield reliable relative values. On April 2, 1917, the soil, which is a heavy clay loam rich in silt and having a lime requirement of about 3000 pounds to the acre (Veitch), was brought up to 30 per cent moisture content on the oven-dry basis. Four of the cans were seeded to White Russian oats. A half-inch layer of quartz sand was then spread over the surface of the soil in the eight cans. From April 12 to September 28 the samples were taken twice a week. From September 29 the sampHng was done approxunately once in two weeks imtil February 7, 1918, after which date the samples were again taken twice a week. The second crop of oats was planted on January 9. Some fifty seeds were usually sown, and the plants were thinned out in the course of two weeks to fifteen in each can. In the season of 1917, one plant became infected with smut, and on June 13 this plant was removed, together with one plant from each of the other cans. To maintain the moisture content of the cropped cans at 30 per cent (oven-dry basis) frequent waterings were necessary, especially at the time of most vigorous growth. At that period the cropped cans were irrigated once a day. The amount of water added was recorded in order to see whether or not there was any relationship between the transpiration and the carbon- 328 H. W. TuBPiN dioxide production in the cropped soil. Since only about a quarter of a pound of water was lost in a week from the uncropped soil, tap water was used m all cases, as the small loss by evaporation could not possibly mtroduce a disturbing element in the form of an accumulation of soluble salts in the soil. Results On each date of sampling, the samples were taken in duplicate from each of the eight cans. Thus eight samples were obtained from the cropped soil and eight from the bare soil. Smce all of the four cropped cans were treated in identically the same manner, the data for the duphcate samples from the cropped cans were averaged. This was done also in the case of the bare soil. It seemed fair to average the data obtained from the cans in each set because m all cases the differences were small. This is shown by the very small probable error. The data for the oat crops of 1917 and 1918 are given m tables 1 and 2 (appcmdix, pages 353 to 356), each figure for carbon dioxide m these two tables being the average of eight determinations. Ihese summarized results are represented diagrammatically in figures 45 and 47. Effect of crop The content of carbon dioxide at the beginning of the experiment was U..b per cent by volmne for both cropped and uncropped soil. From that oime on, as may be seen from figiures 46 and 47, the amount of carbon dioxide in the uncropped soil in no case reached that in the cropped soil — not even after the removal of the crop. The latter point may perhaps be explained by the fact that since the roots of the crop were not removed trom the soU at harvesting, they somewhat increased the available supply of organic matter. The results reported here are directly opposite to those of Bizzell and Lyon (1918), who worked with the same Dunkii-k clay loam under field conditions and found that subsequent to the removal ot the oat crop a marked decrease in carbon dioxide below that in the uncropped soil took place. This was not found to be the case, however with the Volusia silt loam used by these investigators A study of figure 46 shows that in the season of 1917 there was a marked mci-ease m the carbon dioxide in the cropped soil from the beginning of May, amonth after seeding, until the maximimi, 2 per cent, was reached The" Carbon Dioxide of the Soil Aih 329 April May Juuo July AfS- Sept. Oct. I Fig. 46. caebon dioxide in air from Dunkirk clay loam cropped to from the same soil left bare, w17 Fer cent of CO2 ov. Dee. OATS AND Oaf crop - A/o crop ■ y9/3 Fig. Feb. March April May June July 47. aARBON DIOXIDE IN AIR FROM DUNKIRK CLAY LOAM CROPPED TO FROM THE SAME SOIL LEFT BARE, 1918 Aug. OATS AND 330 H. W. TuEPiN in the first week of June, at the time when the plants were starting to head. Thereafter the general tendency of the curve for the cropped soil was toward a decrease, altho it was not until the middle of July, two weeks previous to harvesting, that this decrease was very marked. It was pointed out by Russell and Appleyard (1917) that in their experiments a large increase in carbon dioxide was observed in the cropped soil at the time of ripening; but, as can be seen from figures 46 and 47, in neither 1917 nor 1918 was any such increase noted in this work. If anything, the ripening was accompanied by a marked decrease in carbon dioxide' as is shown especially for the season of 1918 (fig. 47). Subsequent to the removal of the crop, the carbon dioxide in the cropped soil con- tinued to decrease, but never to a point below or equal to that in the uncropped soil. It is interesting to note that in 1917, fluctuations in the content of carbon dioxide in the uncropped soil were accompanied by similar variations in the cropped soil during the early part of the season and subsequent to harvestmg. This was not true during the period of active growth of the plant, which would seem to indicate that at that time the life activity of the crop itself, rather than that of the soil organisms, is playing the dominant part in controUing the production of carbon dioxide. What has been said for the season of 1917 holds for 1918 also. During the latter season, however, there was a much more marked increase in the carbon dioxide of the cropped soil. By the 1 1th of April, three months after seeding, more than 3 per cent of carbon dioxide was found, as com- pared with a Httle less than 0.2 per cent in the uncropped soU This occurred four weeks previous to heading. Thereafter the content of carbon dioxide in the cropped soil increased to the maximum of 3 34 per cent, which occurred a week before heading and coincident with the tune of rapid elongation of the cuhns. Following the maximum there was a steady dechne. The decrease was especiaUy marked dming early June, when the upper glumes were beginning to turn yellow and the plants were starting to mature. In figure 44 (page 325) the plants are shown a month before the period of maximum carbon-dioxide production. Since the maximum of 3.34 per cent of carbon dioxide found in the soil was about the same as that noted by BizzeU and Lyon (1918) in 'their studies with Dunkirk clay loam cropped to oats, it is evident that the decrease m the production of carbon dioxide in the cropped soil below The Carbon Dioxide of the Soil Air 331 that in the uncropped soil after the removal of the crop, reported by these investigators, may not be due to interference with bacterial activities, since in the work reported in the present paper no such action on the soil organisms, as evidenced by a decrease in carbon-dioxide production, was observed. It may be possible that the decrease noted by BizzeU and Lyon was due to some other eifect of the crop, such as, for example, the reduction of the soil moisture. It has been pointed out in the review of the literature of the subject that some investigators have noted a decrease in carbon dioxide where the moisture was reduced below a certain optimiun amount. On referring to figure 46 it will be seen that early in July, 1917, the carbon dioxide in the cropped soil showed a marked decrease. Tliis was due to the drying-out of the soil when, thru an over- sight, it was not watered for two days. It has been pointed out that the carbon dioxide in the cropped soil was somewhat higher (about 30 per cent) in 1918 than it was in 1917. The results for the two seasons are not strictly comparable, because in 1917 the crop was sown in April whereas in 1918 the seeding was made in January. Also, in 1917 the number of plants was reduced to fourteen in each pot, while in 1918 there were fifteen. However, the total dry weight of the mature crop from the four cans in 1917 was 494.5 grams, as against 416 grams in 1918. Carbon-dioxide and water relationships As has already been stated, a record was kept of the amount of water added to the cropped cans in order to maintain them at a moisture content of 30 per cent (oven-dry basis). The sand mulch on the soil, as has been pointed out also, was so effective that the loss ia moisture on the cropped cans could be regarded as due entirely to transpnation. The total amount of water lost on the cropped cans each week was determined in 1917 and 1918 for a period of ten weeks during which the crop was making the most active growth. These amounts, together with the average weekly content of carbon dioxide in the cropped and the uncropped soil, are indicated in tables 3 and 4 (appendix, pages 357 to 358) , coliunns A, C, and E. The difference between the carbon dioxide in the cropped and that in the uncropped soil is given in column F of the same tables. The carbon dioxide produced to each poimd of water used is shown in colunms G and H. The figiires in colimm G were obtained 332 H. W. TtmpiN by dividing the weekly carbon-dioxide percentage in the cropped soil after the carbon dioxide in the bare soil had been subtracted, by the weeldy loss of water in pounds. The figures in column H, however, were obtained by dividing the weekly carbon-dioxide percentage in the cropped soil by the weekly loss of water without first subtracting the carbon dioxide in the bare soil from that in the cropped soil. The relationship between the carbon dioxide produced in the cropped soil (from which has been subtracted the carbon dioxide in the bare soil), and the water transpired by the crop, is shown graphically in figures 48 and 49. There seems to be a relationship between the amount of water transpired and the carbon dioxide produced by plants, as is indicated Per cent ofCOj Pounds of water 2.6- y\^ 2.5- / \ 2.4- / N. 2.3l / N. 2.2- / ^^ 2.1- / ■ \^ 2.0- ^,^.-^ \ 1.9- y^'""^ \ 1.8- y^ \ 1.7- / 1.6- J^ 1.5- ^^ 1.4- ^^ 1.3- 1.2- /^ ..... 1.1- 1.0- r~~~-~^ y"' ■•.. .,•••■■■' 0.9- / -■ '■-.•■' 0.8- / 0.7- /••''"' 0.6- / .•''' 0.5- 0.4- 0.3- 0.2- 0.1- 40 30 May June .)uiy Fig. 48. relation between watek tkanspibed and carbon dioxide produced BY AN oat crop FOR THE TEN WEEKS DURING WHICH ITS GROWTH WAS MOST VIG- OROUS, 1917 by tables 3 and 4 and by figures 48 and 49. The illustrations show that the curves for the water transpired each week, and for the carbon dioxide obtained by subtracting the carbon dioxide in the bare soil from that in the cropped soil, follow each other closely. The data given in the The Carbon Dioxide of the Soil Air 333 tables and plotted in the curves are for the period of ten weeks during which the plants were growing most actively. Before and after this period no relationship was found to exist between the amount of water transpired and the carbon dioxide produced by the plants. Ter cent ofCOj of v.iur Fig. 49. relation between water transpired and carbon dioxide produced BT AN oat crop FOR THE TEN WEEKS DURING WHICH ITS GROWTH WAS MOST VIG- OROUS, 191S It is seen in columns G and H of tables 3 and 4 that the percentage of carbon dioxide produced to each pound of water transpired, approaches a constant much more nearly when the carbon dioxide in the uncropped soil is subtracted from that in the cropped soil. The smaller coefficients of variability of 22.5 d= 3.74 as compared with 37.4 ± 5.65 in 1917, and 15.1 ± 2.32 as against 19.17 ± 3.12 m 1918, bring out this fact fairly clearly. If it is assumed that the amount of carbon dioxide produced and the amount of water transpu-ed are indications of hfe activity, then the relationships found between the carbon dioxide in the soil, and the water transpired, would hold only when the carbon dioxide is produced 334 H- W. TuRPiN by the crop alone. When the carbon dioxide in the uncropped soil was subtracted from the carbon dioxide found in the cropped soil, and this figure was divided by the amount of water transpired, there resulted approximately a constant of 0.024 ± .0012 (column G) with a coefficient of variability of 22.5 ± 3.74 for 1917, and a constant of 0.043 ± .0014 with a coefficient of variability of 15.1 ± 2.32 for 1918. When the carbon dioxide in the uncropped soil, which may be attributed to bacterial activity, was not subtracted (column H), there resulted a constant of 0.042 ± .0031 with a coefficient of variabihty of 37.4 ± 5.65 for 1917, and a constant of 0.053 ± .0022 with a coefficient of variabihty of 19.17 ± 3.12 for 1918. This shows that the constants in the latter cases are not nearly so dependable as those in the former, indicating that the carbon dioxide produced by the crop is probably the difference between the carbon dioxide in the cropped soil and that in the bare soil. That the values obtained are not perfect constants can hardly be wondered at when it is recalled that the carbon dioxide as determined was not absolute, but relative. In this connection it may be pointed out that there seems to be some groimd for concluding that there is a relationship between the water transpired by the plant and the carbon-dioxide content of the soil. While it is not disputed that the mechanism by which the water is actually lost from the leaves of the plant is purely physical and not at all associated with vital plant activity, yet the process by which the water is brought into the leaves and into a condition to be transpired may weU be considered as being associated with the life activities of the plant. Many investigators have maintained that there is a distinct relationship between the life activities of plants and the water transpired. For example, as early as 1849 Lawes (1850) considered that the comparative rate of transpiration of water to some extent indicated the relative activity of the processes of the plant. He drew these conclusions from studies with wheat, barley, beans, peas, and clover, in which he compared the amount of ash and dry matter obtained from the plants with the water given off by them. He found that the larger the amoxmt of dry matter, the greater was the quantity of water transpired. These views are supported by the investigations of Sorauer (1878, 1880), but the work of Walter Wollnjr (1898) leads to an opposite conclusion. In 1905 Livingston (1905) worked with wheat seedlings and concluded that total transpiration is as good a criterion for comparing the relative growth of plants in The Carbon Dioxide of the Soil Am 335 different media as is the weight of the plant itself. Hasselbring (1914), however, after growing plants under cheesecloth and in the open, stated that the mere passage of water thru the plant had no influence on the assimilatory activity of the plant, provided the water supply did not fall below a certain minimum required to maintain turgor of the cells. Stoklasa and Ernest (1909) determined the carbon dioxide given off by different plants grown in various nutrient solutions, and obtained the results presented in table 5 (appendix, page 358). These figures show that there is a definite relationship between the total dry weight of different crops and the carbon dioxide produced. The average of 0.037 milligram of carbon dioxide to each milhgram of dry matter seems to be independent of the kind of plant used in the test. From the short review given, it would seem that the evidence is in favor of the assumption that transpiration is related to life activity of plants as indicated by a relationship between the dry matter and the water transpired. The work of Stoklasa and Ernest (1909) would point to a correlation between the carbon dioxide produced and the dry matter in the plant. Effect of temperature and atmospheric pressure The relationship between the temperature and the atmospheric pressure at the time of samphng, and the carbon dioxide in the air of the uncropped soil, is shown graphically in figures 50 and 51 for the seasons of 1917 and 1918, respectively. The temperature at each time of sampling was found to be approximately representative of the temperature for the preceding twelve-hours period. The pressure also would probably represent the average of several hours preceding the samphng. On the whole the figures bring out only a few striking facts. High temperatures were usually accompanied by a high percentage of carbon dioxide, while high atmospheric pressures were usually associated with a low carbon-dioxide content. High pressures along with high tem- peratures gave fairly high contents of carbon dioxide, indicating that temperature has a more marked effect than pressure. When the temper- ature and the pressure were medium there appeared to be no relationship with the carbon-dioxide content. Very low temperatures were always accompanied by a low content of carbon dioxide; but, while a very low pressure did not necessarily mean a high carbon-dioxide content, it was usually associated with such a condition. 336 li. W. TuRPiw Per cent of 00= 2 2 2,0 LS 1 6 1.4 1.2 1.0 0-8 0.6 OAi 0.2 ^f/r7c?s/^/yffr/c /:?rff^:y Si/re — 1 ;i I J ^ I April May June .Tu!y j_i_y_ Temp. fC.) Mm. pr. (inches) 36° •34° 29.6 •32° •30° 29.4 • 28° ■26° 29.2 24° 22° 23.0 20° 18° 28.8 16° 14° 28.6 Fig. 50. relation between the tempekatukb of tse soil at ths time of "sampling, the atmospheric pressure, and the carbon dioxide in the air op the uncropped SOIL, 1917 Per cent" ofCC: 1.1 1.0 0.9- 0,8- 0.7- 0.6 0,5 0.4 0.3 0.2 0.1 _ Temp Atm. pr. "(C.) (inches) C'P/-£'C3^ cf/ox/o'tr 7jvT?/:>e/r^/t//yT Fig. 51. relation between the temperature of the soil at the time of sampling, the atmospheric pbessube, and the carbon dioxide in the aib of the uncbopped SOIL, 1918 The Carbon Dioxide of the Soil Air 337 Summary oj experiment 1 The results of the first experiment may be siimmarized as follows: 1. Soils cropped to oats always contained a greater amount of carbon dioxide than did the corresponding bare soils. 2. The crop had a residual effect, increasing the carbon-dioxide content above that in the uncropped soil. 3. The difference between the amount of carbon dioxide in the cropped soil and that in the uncropped soil at the period of most active crop growth, divided by the amount of water transpired by the crop, gave an apparent constant which varied with the season. 4. The fact just stated may indicate that the difference between the amount of carbon dioxide produced in the cropped soil and that in the uncropped soil represented the amount produced by the crop. 5. It is thus evident that the carbon dioxide from plants and from soil organisms accumulated independently. 6. Fluctuations in the amount of carbon dioxide in the uncropped soil were due largely to temperature and pressure variations. High pressures produced low contents of carbon dioxide, while high temperatures caused high production of carbon dioxide, and vice versa. EXPERIMENT 2 The object of the second experiment was to determine the influence of some crop other than oats on the production of carbon dioxide. The crop used in this case was common millet {Setaria italica). Immediately after the harvesting of the 1918 oat crop, millet was planted on the same soil and in the same cyHnders as were used in experiment 1. For experiment 2 the sm-face layer of Sand was entirely removed from the soil, which was then thoroly stirred to a depth of about three inches. The millet was seeded on four of the soils, of which two had previously been in oats and two had been bare. The object in using these two different sets was to try to produce some differences in the two crops of millet. It was thought that possibly the millet growing on the soil which had been previously cropped twice to oats, might not grow well, and in such a case a comparison could be made between a good and a poor crop of millet. 338 H. W. TURPIN Fig. 52. millet crops six weeks after seeding, on the two soils having high and LOW initial contents of carbon dioxide, respectively Close view, showing details The crop was planted on July 1. Within three weeks after planting, the crop on each can had been thinned out until forty plants remained. The number of plants to a pot was reduced in the next week to thirty. At first the samples were taken twice a week, as in the case of experi- ment 1 ; but later — from the middle of August — when the crop was making very rapid growth, samples were taken every day. Toward the end of August the samples were taken every other day. As in experi- ment 1, the moisture in the soil was maintained at 30 per cent (oven- dry basis). At the time when the experiment was discontinued, the plants were completely headed. In the case of series 1 (soil previously cropped to oats) the plants were beginning to show signs of maturing; in series 2 (soil previously bare), however, the grain was still between the milk stage and the dough stage. The crops on series 1 and 2 were identical in all details until a few days after heading. This may be seen in figures 52 to 55. Thereafter the plants in series 2 maintained their dark green color, while those in The Cakbon Dioxide of the Soil Air 339 Fig. 53. millet chops six weeks after seeding, on the two soils having high and LOW initial contents of carbon dioxide, respectively Same as figure 52, but showing cylinders series 1 gradually became light green, until finally, when the experiment was stopped in September, the latter were beginning to mature while those in series 2 had not yet begun to show signs of ripening. Results The results of experiment 2 are summarized in table 6 (appendix, page 359), in which each figure represents the average of two duplicate samplings from each of two pots, an average of four samplings in all. 340 H. W. TUEPIN ■Fig. 54. Millet crops seven and one-half v>fEEK3 aftjsr seeding, on the two soils HAVING HIGH AND LOW INITIAL CONTENTS OF CARBON DIOXIDE, RESPECTIVELY Close view, showing details These data arc presented diagrammatically in figures 50, 57, and 58, the first two representing the data for series 1 and 2, respectively, and the third giving these two sets of curves on one sheet. It will be noticed that the carbon dioxide in the cropped soils and that in the uncropped soils remained the same for the first four weeks after seeding. Thereafter the curves, for the cropped soils separated fairly rapidly from those for the bare soils. In this respect there is no difference between the oats and the millet. It will be observed, however, that whereas the two oat crops attained their point of maximum carbon- dioxide production shortly before heading, the miUet crops both gave the most carbon dioxide just ten days after heading. In order to bring out this point more clearly, curves showing the relationship between the amount of carbon dioxide in the oaf soil (1917) and that. in the millet soil (series 2) have been plotted together in figui-e 59, in such a manner that the carbon dioxide produced at the period of heading of each of the two crops is on the same ordinate, with the data for a few weeks The Cabbon Dioxide of the Soil Aih 241 Fig. 55. millet crops seven and one-half weeks after seeding, on the two soils having high and low initial contents of carbon dioxide, respectively Same as figure 6i. but showing cylinders before and a few weeks after the heading period plotted to the left and to the right of this point, respectively. Since the experiment was discontinued before the millet crops matured, it is not possible to say whether or not the curve for the later period of 342 H. W. TuKPm Per cent ofCOs 4.S 4 fi- /////£•/ 4.4- A/oCro/^ o^ /h/hfy CO -so// 4.2- - ^ 4.0- 3.8- |- a.fi- &s 3.4- 3.2- 1 ^ 3.0- t f X 2.8- 2.6- 2.4- §- "1 > / \ 2.2- 2.0- ^ /-^ \J V 1 S- ^ ^ ^ 1.6- I /■■•• ' ' "' \ / 1.4- ^ / •V / / '" 1.2- ^ / ' ^"*'*'v/ * 1.0- 0.8- L/ '•. / ••.._ .-■■■••••. 0.6 • 0.4- 0.2- July August tiept. ElG. 56. CARBON DIOXIDE IN AIR FROM DUNKIRK CLAY LOAM PHE-V10USLT CROPPED TWICE TO OATS, CROPPED TO MILLET, AND FROM THE SAME SOIL LEFT BARE, 1918 Per cent of CO2 4.6n 4.4-1 -( '' Af/'/M/nrp 4.0- A/a cz-o/? o/y /cjf^CO so/V 3.8- 3.6- 1 3.4- 3.2^ zM 2.8- $ 2.6- > /\ 2.4- ^^ /\ 2.2- ^ 1 \ 1 / ^---^ 2.0- 1.8- 1 1.6- 1.4- -r A^ i y 1.2- ^ / ^ 1.0- 8 0,8- ^ ^iT^'*''*'^" ^'^ — -J 0.6- *., •-. 0.4- *'-..•• '• •••..•• 0.2- )\. -^ n July August Sept. Fig. 57. CARBON DIOXIDE IN AIK FROM DUNKIRK CLAY LOAM NOT PBE-VIOUSLT CROPPED, CEOPPED TO MILLET, AND FROM THE SAME SOIL LEFT BABE, 1918 The Carbon Dioxide of the Soil Air 343 Per cent of CO3 h/^/7 CO ^o// /o^ CO so// A/oprqp or? /7/hr/7 CO^^o// -./ zr July zxz '^r . August Fig. 58. relation between the amounts of carbon dioxide in air from cropped and from uncropped dunkirk clat loam having high and low initial contents of carbon dioxide, respectively Oaf crop, /9/r ■ 4321 1234 Weeks before heading Weeks after heading Fig. 59. relation between the amounts of carbon dioxide in air from dun- kirk CLAY loam cropped TO OATS AND MILLET, RESPECTIVELY, BEFORE AND AFTER THE CROPS HEADED 344 H. W. TxjBPiN growth of the millet would resemble in genera] that for the oat crops. The general tendency of the cm-ve after August 25 was to fall as the plants advanced toward maturity, as in the case of the oat crops. It will be noticed from figure 59 that the actual amount of carbon dioxide produced on the soil cropped to mUlet was much the same as that produced on the oat son. The maxima for the two pat crops of 1917 and 1918 were, respectively, 2.031 per cent and 3.343 per cent, while the corresponding figures for the millet crops in series 1 and 2 were 3.345 per cent and 2.715 per cent. It must be remembered, however, that there were but fifteen oat plants as compared with thirty millet plants; so that it may be con- cluded that an individual oat plant causes the production of about twice as much carbon dioxide as is produced by a miUet plant. Summary of experiment 2 From the results of the second experiment it may be concluded that a soil cropped to millet causes about the same fluctuations in carbon- dioxide production as are found in a soil growing an oat crop. In general, however, the oat crop gives the greatest production of carbon dioxide previous to headmg, while the millet has its most marked effect a week or two after heading. It would seem also that an individual millet plant causes the production of approximately haK as much carbon dioxide as an mdividual oat plant. From the close agreement between the two curves shown in figures 56, 57, and 58, for series 1 and 2, it may be assumed that in spite of shght differences in the previous treatment of the soil the excess carbon dioxide due to the crop was fairly shnilar where the crops growing showed no apparent differences m vigor. This is indicated also m figures 62 to 55, which show the two crops at an early and at a later stage of growth, the crop on the soil previously cropped twice to oats being designated as a high-carbon-dioxide crop and that on the soil that was previously bare being called a low-carbon-dioxide crop. EXPERIMENT 3 As is pointed out in the review of Uterature, it is not clear whether or not the increased amount of carbon dioxide observed in a cropped soil is due to the excretion of carbon dioxide by plant roots (plant activity) or to the decay of root particles from the growing crop (bacterial activity). Data obtained in experiment 3 seem to throwa httle fight on tins question. In this experiment, cans 1, 2, 3, and 4, which had previously grown two The Caebon Dioxide of the Soil Air 345 crops of oats, had a considerably higher content of carbon dioxide, even after the removal of the crop and especially for about two months after harvest, than did cans 5, 6, 7, and 8, which remained imcropped for the two seasons. After the oat crop from cans 1, 2, 3, and 4 was harvested, on July 1, 1918, cans 2 and 3, and the uncropped cans 6 and 8, were seeded to millet. Cans 1, 2, 3, and 4 are here designated as the high-carbon-dioxide series, while cans 5, 6, 7, and 8 are called the low-carbon-dioxide series. Thus, in the high-carbon-dioxide series, cans 1 and 4 were bare and cans 2 and 3 were cropped to millet; in the low-carbon-dioxide series, cans 5 and 7 were bare and cans 6 and 8 were cropped. All these cans were sampled in the usual way for carbon dioxide, and the data obtained are given in table 7 (appendix, page 360). The samples were taken twice a week at first, and later they were taken daily. The moisture in the soil was maintained at or near 30 per cent (oven-dry basis). Within a month of seeding, the crop was thinned to thirty plants to a can; so that at the time when the effect of the plants on the carbon dioxide became noticeable (a month after seeding), the number of plants was the same for all cans. Results In table 7 it is shown that the differences between the percentages of car- bon dioxide in the cropped soil and those in the uncropped soil in the high- carbon-dioxide series, were approximately the same as the corresponding differences in the low-carbon-dioxide series. .In table 8 (appendix, page 361) it is seen that the majority of the differences in carbon-dioxide production by the crop in the two series (as determined by the difference between the amount of carbon dioxide produced by the cropped soil and that produced by the uncropped soil) was well witliin the hmits of the experimental error. It seems, therefore, that the crops produced carbon dioxide quite independ- ently, and that this production was not affected by the amount of carbon dioxide in the soil, at least not within the limits set by this experiment. How closely the difference between the curves for the cropped soUs cor- responded with those for the bare soils is shown in figure 58 (page 343). The relationship between the temperature of the soil at the time of sampling, and the carbon dioxide in the bare soil and also that due to the crop on the Tow-carbon-dioxide series (determined by the difference as 346 H. W. TURPIN explained above), is shown in table 9 (appendix, page 362) and in figure 60. It will be noticed that increases in temperature were more frequently accompanied by rises in carbon dioxide in the bare soil (indicating a relationship between bacterial activity and carbon-dioxide production), than by rises in the carbon dioxide produced by the crop. In the latter Cc7rhc!rr c/zox/C^S /"/-c/r? rr?///^/- crop — Temp. fC.) 36° 35° 34° 33° 32° 31° 30° -29° -28° -27° 26° 25° 24° 23° 22° 21° 20° 1 12 15 19 26 August Fig. 60. eelation between the carbon dioxide produced bt a millet crop, the carbon dioxide in a bare soil, and the temperature op the soil at the time of sampling, 191s case no such close relationship appeared, but the carbon dioxide increased gradually as the age of the plant advanced until the point of maximum carbon-dioxide production, after which there was a decline. This increase in carbon dioxide seems to have kept pace with the rate of growth of the plants. At the time when the plants ceased to grow actively (some time after heading), the carbon-dioxide production also fell off. If the excess The Carbon Dioxide op the Soil Air 347 carbon dioxide in the cropped soil is due to the decomposition by bac- teria of root particles tin-own off from the growmg crop, then one would expect to find that those factors which produce fluctuations in the carbon dioxide in the bare soil would produce corresponding, but more magni- fied, fluctuations in the cropped soil. But, as is pointed out above, a factor such as temperature did not produce corresponding changes in the two soils. Again, if the decomposition of root particles from the growing crop gave rise to the increase of carbon dioxide in the cropped soil, it is reason- able to suppose that there would be a much larger increase in carbon dioxide at a time when the roots were beginning to die off rapidly, that is, toward the ripening period. Such, however, was not the case. Summary of experiment S It is probable, therefore, that the larger part of the excess carbon dioxide produced in a cropped soil is due to respu-atory activities of the plant roots, and that the amount resulting from the decay of root particles from the growing crop is small — altho after the crop has matured, any excess of carbon dioxide found is undoubtedly due to the decay of the mass of roots left in the soil. This excess, however, is very small when compared with the very large amounts of carbon dioxide found in the cropped soil at the time of heading, for example. In support of the conclusion that the larger production of carbon dioxide in the cropped soil is due to respiratory activities of the plant roots, the data presented in experiment 1 show that there seems to be a correlation between the. water requirements of the plant, and the amount of carbon dioxide produced. GENERAL SOIIV'IAEY The results of the work reported in tliis paper with regard to the effect of crop and other factors on the production of carbon dioxide in a Dunkirk clay loam maintained at a constant moisture content of 30 per cent (oven- dry basis), may be sununed up as follows: 1. An oat crop increased the production of carbon dioxide in the soil. This increase became marked after the first month from the time of seeding, and increased to a maximum just previous to or after the plants headed, after which there was a gradual decline. 348 H. W. TuRPiN 2. Millet produced about the same increase in carbon dioxide as did oats, but the production of carbon dioxide by each millet plant was approximately half as much as the production by each oat plant. The most marked rise in the carbon-dioxide content of the soil occiured at a later period of growth in the case of the millet than in the ease of the oats. 3. The cropped soil, after the crop was harvested, maintained a higher carbon-dioxide content than was found in the bare soil. This was due probably to the decomposition of plant roots left in the soil. 4. It would seem that increased plant activity (growth) is accompanied by increased carbon-dioxide production. This theory is supported by the fact that a relationship was shown between the carbon dioxide pro- duced presumably by the crop, and the water transpired. 5. Fluctuations in the content of carbon dioxide in the bare soil were accompanied by sLmUar fluctuations in the cropped soil only after the removal of the crop and before the crop had made much growth. 6. There appeared to be httle relationship between the temperature of the soil at the time of samphng, and the carbon dioxide in the cropped soil or that assumed to be produced by the crop (determined by sub- tracting the carbon dioxide in the bare soil from that in the cropped soil). 7. In the bare soil the carbon dioxide was usually high dm-ing warm weather and low when the temperature decreased. 8. Very low atmospheric pressures were usually accompanied by an increase in the content of carbon dioxide in the bare soil. 9. The carbon dioxide produced presumably by the plant was about the same in soils having a high initial carbon-dioxide content as in those low in carbon dioxide, indicating the probabihty that plants and soil organisms act independently in producing carbon dioxide. 10. It is concluded from this work that the plant itself, and soil organisms, produce most of the carbon dioxide in the soil; that the plant often produces at the period of its most active growth many times as much- carbon dioxide as is produced by soil organisms; and that the excess carbon dioxide in the soil growing a crop is due to respiratory activity of the plants rather than to the decay of root particles from the crop growing on the soil at the time of analysis. 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Methoden zur Bestimmimg der Atinimgsintensitat der Bakterien im Boden. Ztschr. landw. Versuchsw. Oesterreich 14: 124.3-1279. 1911. Stoklasa, Julius, and Ernest, Adolf. Ueber den Ursprimg, die Menge, und die Bedeutung des Kohlendioxyds im Boden. Centbl. Bakt. 2:14:723-736. 1905. The Carbon Dioxide of the Soil Air 351 Beitrage zur Losuns; der Frage der chemischen Natur des Wurzelsekretes. Jahrb. wiss. Bot. [Pringsheim] 46:55-l'02. 1909. Suchtelen, F. H. Hesselink van. tJber die Messung der Leben- statigkeit der aerobiotischeii Bakterien im Boden durch die Kohlensau- reproduktioii. Centbl. Bakt. 2:28:45-89. 1910. WoLLNY, E. Untersuchungen iibsr den Einfiuss der Pflanzendecke und - der Beschattung auf den Kohlensauregehalt der Bodenluft. Forsch. Geb. Agr.-Physik 3 : 1-14. 1880 a. Untersuchungen uber den Kohlensauregehalt der Bodenluft. Landw. Vers. Stat. 25:373-391. 1880 b. Die Zersetzung der organischen Stoffe und die Humus- bildungen, p. 1-179. 1897. WoLLNY, Walter. Untersuchungen iiber den Einfiuss der Luftfeuchtig- keit auf das Wachsthum der Pflanzen, p. 1-44. Inaug. Diss., Halle. 1898. The Caebojst Dioxide of the Soil Air 353 APPENDIX Carbon Dioxide (Per Cent by Volume) in Cropped and in XJncropped Soil (Oats, 1917) Temper- Atmos- ature pheric (centi- pres- grade) sure (inches) 22 0° 29. OG 23.0° 28.78 23.0° 28.98 30.0° 29.22 21.0° 29.12 22.0° 29.06 23.0° 29.02 17.0° 29.15 21.5° 29.16 22.0° 28.82 30.0° 28.88 16.0° 29.00 21.0° 29.05 16.0° 28.78 17.0° 28.77 20.0° 29.07 29.0° 29.27 21.0° 28.88 22 0° 29.10 13.0° 29.07 22.0° 29.17 20.5° 29.15 30.0° 29.55 20.0° 28.91 28.0° 28.92 16.0° 29.16 24.0° 28.95 19.0° 28.92 30.0° 29.14 20.0° 29.24 35.0° 29.05 23.0° 28.99 35.0° 28.93 21.0° 29.07 25.0° 29.22 19.5° 29.05 26.0° 29.21 20.5° 29.00 32.0° 28.97 22.0° 28.71 Water added to maintain moisture content at 30 per cent (grams) Carbon dioxide produced in Cropped soil (A) XJncropped soil (B) Difference (A-B) 1.75 2.75 3.00 4.50 3.75 2.50 5.75 7.25 11.00 16.75 14.00 11.25 14.50 20.25 15.75 23.75 20.75 27.00 20.50 31.25 27.00 39.50 24.00 '25'00 20.00 16.00 7.50 8.00 6.00 3.50 6.00 3.50 1.50 2.75 1.25 0.2S5±;009 0.909±.017 0.526±.007 0.741±.019 0.698±.017 0.813±.013 0.737±.014 0.640±.013 0.943±.027 0.931±.037 1.422±.048 1.16G±.047 1.034±.037 1.307±.040 1.297±.034 2.031±.102 1.708±.0e0 1.982±.101 1.365±.042 1.292±.024 1.315±.025 1.809±.030 1.412±.033 1.846±.028 1.778±.032 0.799 1.614d=.014 1.699±.018 1.7S1±.052 1.111±.016 1.595±.030 1.261±.044 1.475±.029 1.040±.032 1.028±.02S 0.706±.012 0.876±.012 0.781±.019 0.909±.012 0.765±.013 0.281±.006 0.777±.014 0.498±.009 0.736±.003 0.653±.004 0.714±.008 O.6.53±.007 0.559±.007 0.776±.009 0.632±.006 0.87S±.015 0.475±.003 0.452±.003 0.415±.004 0.477±.002 0.648±.007 0.698±.011 O.530±.0O2 0.452±.005 0.416±.002 0.419±.007 0.4SO±.009 0.466±.007 0.496±.003 0.620±.008 0.393±.002 0.449±.008 0.394±.001 0.633±.007 0-.491±.005 0.954±.015 0.686±.007 0.959±.007 O.643±.O07 0.629 ±007 0.425±.003 0.581±.005 0,478±,003 0.704±.002 0.526±.007 0.004±.011 0.132±.022 02S±.011 0.005±.019 0.045±.017 0.099±.015 O.OS4±.016 0.081±.015 0.167d=.028 0.299±.037 0.544±.050 0.691±.047 0.5S2±.037 0.S92±.040 0.820d=.034 1.3S3±.102 1.010±.060 1.452±.101 0.913±.043 0.876±.024 0.896±.02e 1.329±.032 0.946±.034 1.350±.02S 1.15S±.033 'i'.165±'6i6 1.305±.018 1.148±.052 0.620±.O17 0.641±.033 0.575±.044 0.516± 030 0.397±.032 0.399=t,029 0.281±-012 0.295±.O13 0,303± 019 0,205±.012 0.239±.015 354 H. W. TUEPIN TABLE 1 (concluded) Temper- ature (centi- grade) Atmos- pheric pres- sxu-e (inches) Water added to maintain moistm-e content at 30 per cent (grams) Carbon dioxide produced in Date of sampHng Cropped soli (A) Uncropped soil (B) Difference (A-B) August 27 August 31 Sept. 3 Sept. 7 Sept. 10 Sept. 14 Sept. 17 Sept. 21 Sept. 24 Sept. 28 Oct. 5 Oct. 19 Nov. 2 Nov. 16 Nov. 30 Dec. 14 • 29.5° 14.0° 25.0° 14.0° 14.5° 15.5° 25.0° 18.0° 24.0° 18.0° 16.0° 24.0° 17.0° 19.0° 17.0° 17.5° 29.20 .29.37 29.21 29.23 29.34 29.41 29.31 29.06 29.40 28.93 28.89 28.92 29.40 29.08 29.15 28.69 0.729±.009 0.345±.007 0.659±.015 0.376±.007 O.2S9±.O04 0.3S5±.010 0.544±.008 0.554±.010 0.415±.003 0.495±.012 0.309±.010 0.404±.010 0.382±.008 0.424±.013 0.280±.008 0.356±.020 0.538±.005 0.244±.001 0.488±.001 O.256±.O03 0.195±.003 0.255±.007- 0.378±.004 0.348±.005 0.266±.003 0.328±.003 0.211dz.004 0.288±.006 0.259±.004 0.301±.016 0.192±.005 0.216±.007 0.191±.010 0.101±.O08 0.171±.015 0.120±.008 0.094±.005 O.1.30±.O13 0.166±.009 0.206±.011 0.149±.004 0.167±.013 0.098±.011 0.116±.011 0.123±.009 0.123±.021 0.0S8±.010 0.140±.021 The Carbon Dioxide of the Soil Air 355 Carbon Dioxide (Per Cent by Volume) in Cropped and in Uncropped Soil (Oats, 1918) Water added to Carbon dioxide produced in Temper- ature Atmos- pheric maintain moisture Date • Difference of (centi- pres- content Cropped Uncropped (A-B) sampling grade) sure at 30 soil soil (inches) per cent (grams) (A) (B) Jan. 3 18.0° 29.24 0.373±.020 0.229±.005 0.144±.021 Jan. 16 18.5° 28.84 0.348±.014 0.162±.002 0.184±.014 Jan. 31 18.0° 29.32 0.315±.009 O.223±.006 0.092±.011 Feb. 7 20.0° 29.20 0.318±.010 0.225±.002 0.092±.010 Feb. 11 20.0° 28.98 0.340±.010 0.249±.009 0.091±.013 Feb. 14 22 5° 28.97 0.401±.010 O.255±.009 0.146±.013 Feb. 18 18.0° 29.68 0.370±.010 ' 0.221±.006 0.149±.012 Feb. 21 20.0° 28.75 "".5!00 0.509±.014 0.258±.008 0.251±.016 Feb. 25 20.5° 28.83 3.75 0.445±.009 0.195±.008 0.250±.011 Feb. 28 20.0° 29.25 5.00 0.595±.010 0.240±.008 0.355±.012 March 4 16.0° 29.34 5.75 0.695±.016 0.236±.008 0.459±.018 March 7 20.0° 28.96 3.25 0.639±.017 O.295±.O07 0.344±.018 March 11 16.0° 29.54 9.75 0.834±.010 0.236d=.008 0.598±.020 March 14 20.0° 28.48 9.75 0.989±.029 0.223±.006 0.743±.029 March 18 18.0° 29.15 14.25 1.688±.027 0.285±.006 1.403±.028 March 21 25.0° 28.88 19.75 2.290±.030 0.471±.012 1.819±.032 March 25 18.0° 28.84 24.00 2.103±.030 0.259±.009 1.844±.031 March 28 21.0° 29.39 17.. 50 2.224rh.055 0.319±.010 1.905±.056 April 1 21.0° 28.81 30.75 2.514±.039 0.331±.010 2.183±.041 April 4 20.0° 29.08 27.00 2.314±.033 0.318±.003 1.996±.034 April 8 19.0° 29.39 33.25 1.855±.025 O.17O±.O09 1.695±.026 April 11 20.5° 29.26 14.00 3.129±.033 0.188±.004 2.941±.034 April 15 20.5° 29.22 22.25 2.704±.072 0.320±.006 2. 384 ±.072 AprU IS 24.0° 28.83 29.75 2.580±.OS5 0.311±.004 2.239±.0S5 April 22 21.0° 28.68 24.25 2.129±.089 0.211±.005 1.918±.0S9 April 25 '23.5° 29.28 15.00 2.678±.056 0.303±.006 2.375±.057 AprU 29 22.5° 28.97 38.50 2.418±.040 0.238±.005 2.182±.041 May 2 23.5° 29.20 21.00 2.0o9±.046 0.211±.003 1.858±.046 May 6 23.0° 29.07 31.00 3.343±.029 0.3S9±.003 2.954±.029 May 9 27.0° 28.93 30.25 2.741±.041 0..345±.004 2.398±.041 May 13 23.0° 28.92 24.25 2. 643 ±.045 0.296d=.004 2.347±.045 May 16 ■ 27.5° 29.41 21.00 2.753±.071 0.283±.004 2.487±.071 May 20 22.0° 29.12 23.00 2.600±.O81 O.276±.O04 2.324±.081 May 23 24.0° 29.30 17.75 2.934±.044 0.295±.008 2.639±.044 May 27 21.5° 29.05 17.25 2.153±.065 0.259±.008 1.894±.065 May .30 23.5° 29.17 16.75 1.51S±.018 0.234±.005 1.254±.018 June 3 20.5° 29.19 27.00 2.045±.011 0.344±.005 1.701±.O12 June 6 22.5° 29.10 18.25 1.331±.015 0.299±.095 1.062±.015 June 10 17.5° 29.11 17.75 1.120±.017 O.199±.003 0.921±.017 June 13 21.5° 28.77 10.75 1.070±.017 0.220±.004 0.850±.018 June 17 19.5° 29.03 15.59 1.170±.007 0,271±.095 O.899±.O09 June 20 24.0° 29.21 11.75 1.001±.OD9 0.249±.002 0.755±.009 June 24 14.0° 29.00 5.50 0.519±,007 0.140d=.002 0.379±.007 356 H. W. TUHPIN TABLE 2 {concluded) Temper- ature (centi- grade) Atmos- pheric pres- sure (inches) Water added to maintain moisture content at 30 per cent (gram.s) Carbon dio.xide produced in Date of sampling Cropped soil (A) Uncropped soil (B) Difference (A-B) June 27 July 1 July 4 July 8 July 11 July 15 July 18 July 22 July 25 July 29 August 1 August 5 August 8 August 12 August 14 August 15 August 16 August 17 August 19 August 21 August 22 August 23 August 24 August 26 August 27 28.0° 20.5° 28.5° 17.0° 21.5° 19.0° 30.0° 23.0° 30.0° 24,0° 30.0° 21.0° 35.0° 23.5° 28.0° 31.0° 32.0° 29.5° 26.5° 33.0° 33.0° 33.0° 34.0° 30.5° 30.0° 29.06 28.84 29.33 28.99 29.12 29.12 28.94 29.31 29.22 29.14 29.07 28.92 29.03 29.16 29.07 29.21 29.16 29.50 29.53 29.21 29.17 29.10 29.02 28.96 29.28 6.00 5.25 1.169±.019 1.500±.041 1.026±.014 0.763±.040 0.745±.024 1.028±.01S 1.430±.040 1.778±.004 1.648d=.035 1.788±.001 1.020±.O38 O.653±.O08 1.563±.013 1.0S8±.02S 1.315±.007 0.S85±.024 0.835±.016 0.760±.021 0.688±.006 0.715±.026 0.8SS±.013 0.988±.004 1.145±.005 0.7SS±.016 O.6SS±.006 0.396±.003 0.369±.006 0.336±.005 0.215±.002 0.295±.007 0.333±.004 0.578±.011 0.750±.021 0.895±.017 0.92Q±.021 0.580±.029 0.375±.017 0.920±.036 0.635±.012 0.790±.026 0.525±.021 0.505±.021 0.478±.023 0.400±.014 0.430±.010 0.588±.018 0.633±.014 0.695±.007 0.468±.006 0.448±.020 0.773±.019 1.131±,041 0.690±.015 0.548±.040 0.450±.025 0.695±.019 0,852±.042 1.028±.021 0.753±.039 0.868±.021 0.440±.048 0.278±.018 0.643±.038 0.423±.030 0.525±.027 0.360±.032 0.330±.028 0.282±.031 0.268±.015 0.285±.028 0.300±.022 0.355±.015 0.450±.009 0.320±.018 0.240±.021 The Carbon Dioxide of the Soil Air 357 TABLE 3. Relation between the Carbon Dioxide in the Cropped Soil during THE Period of Most Active Plant Growth, and the Water Transpired Each Week (Oats, 1917) Date Water trans- pired (grams) Total water trans- pired each week (grams) (A) Cropped soil Carbon dioxide (per cent) (B) Average carbon dioxide for the week (per cent) (C) Uncropped soil Carbon dioxide (per cent) (D) Average carbon dioxide for the week (per cent) (E) Difference in carbon, dioxide C-E Per cent of carbon dioxide to each pound of water _F A _ (G) C A (H) May 7. . May 11. May 14. May IS . May 21 . May 25 . May 28. June 1 . . .Tune 4 . . June 8 . . June 11. June 15 . June 18 . June 22 . June 25 . June 29 . July 2 . . July 6 . . July 9 . . July 13. 5.75 1 7.25 11.00 1 16.75 I 14.00 1 11.25 I 14.50 1 20.25 I 15.75 1 23.75 20.75 1 27.00 I 20.50 1 31.25 I 27.00 1 39.50 24.00 1 25!66 1 20 . 00 ] 13.00 27.75 25.25 34.75 39.50 47.75 51.75 66.30 0.943 1 0.931 ■ 1.422 1.166 1.034 1.314 297 031 J 7081 982 J 365 1 292 I 315 I 809 I 412 1 846] 778 1 1.614 1.699 0.937 1.294 1.174 1.664 1.845 1.329 1.562 1.629 1.657 0.7761 . 632 J 0.878 1 0.475 J 0.452 1 0.415 J 0.4771 0.648 0.698 0.530, 0.452 0.410, 0.419 0.480, 0.466' 0.496 , 0.620 1 0.393 I 0.449 1 0.394 0.704 0.677 0.434 0.563 0.614 0.434 0.450 0.481 0.507 0.422 0.233 0.617 0.740 1.101 1.231 0.895 1.112 1.148 1.235 0.018 0.022 0.029 0,032 0.031 0.019 0.021 0.017 0.027 0.072 0.047 0.046 0.048 0.047 0.028 0.030 0.024 0.037 Mean Standard deviation Coef&cient of variability. 0.024 t.0012 0.0054 ±.0009 22.5 ±3.74 0.042 ±.0031 0.0136 ± . 0022 37.40 ±5.65 358 H. W. Ttirpin TABLE 4 Reiation between the Cabeon Dioxide in the Ckopped Soil during THE Pekiod of Most Active Plant Growth, and the Water Tkanspieed Each Week (Oats, 1918) Date March 4 March 7 March 11 March 14 March IS March 21 March 25 March 28 April 1 April 4 April 8 April 11 April 15 AprU 18 AprU 22 April 25 April 29 May 2 May 6 May 9 Water trans- pired (grams) 5.75 3.25 9.75 9.75 14.25' 19.75 24.00 17.50 30.75' 27.00 33.25' 14.00 22.25' 29.75 24.25 15.00 38.50' 21.00 31.00' 30.25 Total water trans- pired each week (grams) (A) 9.00 19.50 34.00 41.50 57.75 47.25 52.00 39.25 59.50 61.25 Cropped soil Carbon dioxide (per cent) (B) 0.695' 0.639 . 834 ' 0.969 1.688' 2.290 2.103 2.224 2.514' 2.314 1.865' 3.129 2.704' 2.. 580 2.129' 2.678 2.418' 2.069 3.343' 2.741 Average carbon dioxide for the weelc (per cent) (C) 0.667 0.902 1.989 2.164 2.414 2.497 2.642 2.404 2.244 3.042 TJncropped soil Carbon dioxide (per cent) (D) 0.236 0.205 0.236 0.226 0.285' 0.471 0.259' 0.319 0.331 0.318 0.170' 0.1S8 0.320 0.311 0.211 . 303 0.230' 0.211 0.389' 0.345; Average carbon dioxide for the week (per cent) (E) 0.266 0.231 0.378 0.289 0..325 0.179 0.316 0.257 0.224 0.3G7 Difference in carbon dioxide C-E (F) 0.401 0.671 1.611 1.875 2.089 2.318 2.326 2.147 2.020 2.675 Per cent of carbon dioxide to each pound of water F A (G) Mean Standard deviation Coefficient of variability 0.045 0.034 0.047 0.045 0.036 0.049 0.045 0.055 0.034 0.044 C A (H) 0.043 d=.0014 0.0065 ±.0010 15.1 ±2.32 0.074 0.046 0.059 0.052 0.042 0.053 0.051 0.C61 0.038 0.050 0.053 ±.0022 0.0102 ±.0015 19.17 ±3.12 TABLE 5. Relation between the Drt Weight of the Crop and the Carbon Dioxide Given Off by Pl.u^t Roots (From Stoklasa and Ernest, 1909) Cro-i Barley Rye Oats Wheat Average Total dry matter produced in 84 days (milligrams) 34,493 27,046 28,215 18,375 26,532 Total carbon dioxide produced in S4 days (milligrams) 1,267 1,053 ■793 784 974 Milligrams of carbon dioxide produced to each milligrcm of dry matter 0.037 0.039 0.030 0.043 0.037 The Caebon Dioxide of the Soil Air 359 TABLE 6. Caebon Dioxide (Pee Cent by Volume) in Cropped and in Unceopped Soil (Millet, 191S) Date of sampling Carbon dioade produced in Series 1 (high CO2 soil) Cropped (per cent) Bare (per cent) Series 2 (low CO2 soil) Cropped (per cent) Bare (per cent) JulvS July 11 July 15 July 18 July 22 July 25 July 29 August 1. . . . August 5. . . . August 8. . . . August 12. . . August 14 . . . August 15. . . August 16. . . August 17. . . August 19... August 21. . . August 22. . . August 23. . . August 24. . . August 26. . . August 27. . . August 2S. . . August 29. . . August 31. . . September 3 0.713±.016 0.763±.006 1.045±.031 1.455±.O50 1.803±.032 2.015±.079 1.923±.101 1.305±.055 1.133±.008 2.115±.017 2.025±.021 2.448±.02S 1.864±.016 1.950±.010 2.108±.018 2.040=h.048 2.288±.016 3.098d=.023 3.095±.OGO 3.345±.0.35 2.465±.O05 2.198±.009 2.245±.031 2.093±.039 1.9S3±.011 1.770±.021 0.763±.040 0.745±.024 1.02S±.018 1.430±.040 i.77S±.004 1.648±.035 1.788±.001 1.020±.038 O.653±.O06 1.563±.013 1.088±.028 1.315±.007 0.885±.024 O.S35±.C16 0.760±.021 O.638±.005 0.715±.026 0.88S±.013 0.9S8±.004 1.145±.005 0.7SS±.016 0.6SS±.003 0.690±.036 0.613±.004 0.590±.007 0.533±.011 0.210±.002 O.283±.O01 0.358±.001 0.578±.001 0.79o±.014 0.908±.059 1.008±.054 0.798±.039 0.750±.052 1.62S±.161 1.223±.018 1.710±.043 1.405±.012 1.480±.033 1.683±.049 1.683±.()42 1.948±.016 2.655±.055 2.715±.074 2.690±.060 2.27o±.064 2.133±.075 1.958±.056 2.120±.088 2.245±.114 2.143±.068 0.215±.002 O.295±.O07 0.333±.004 O.578±.O01 O.750±.O21 0.895±.017 0.920±.021 0.580±.029 0.375±.017 0.920±.036 0.665±.012 0.790d=:.026 0.525±.021 0.505±.021 0.478±.023 0-400±.014 0.430±.010 0.5S8±.018 0.633±.014 0.695±.007 0.468±.006 0.448±.020 0.348±.004 O.358±.O06 0.370±.010 0.310±.005 360 H. W. TUBPIN n < D ►J w fcoo ocn « ^ Z E-- p w (.ri "^ ^ 1- la ^ ^ a O "« Q fc z o n a < n .7 e3 o - 1 ooooo>-i^oo^ooooooooooooo -H4i-H-H-H-H-H-ti-H-«-H+l-H-H-H-H-H-H-ii-H-H-H-H OOOOOC0OO'-''-iC0'M^T-HTHOO'-^OfMr-tr-(O ooooooooooooooooooooooo I + 1 + 1 ++++ 1 ++++++++++ 1 1 1 OOO-— KNOiOrfint^tNiOIMCOiOTtii— (lOt^OCCir—LO OOOOOOOOOi-HOOOOOOOOOOOOO ■ti-H-H-H-ti-H-ti-H-H-H-H-H-H-H-H-H-H-H-H-ti-H-W-H ioiMiooioirccocoiocooooo»o»occciot>oi"m--»-':tc 0'-i(NO"*i-'cO'-Hi>.0'f:i'MoCir-oco--ioooaiOcC'-' OOOOOOOC-" 1— I c-i CM o CO cc c/i "O CO ^: t^ "— t -+ c— r— --H o o t~- ^^ "^ OOOOOCO-— "C5'OOOOr*GO-^'N'^'*'-'3CCCO'M(NC^lCOCOTfCO£MCO dooO'T'Opppppoooooooooooo OC5r-f'-«iOCl"^t~-— IQC-Di.OCOCl^-HOlrtOtNl-OCOCOtOCDfMOC^OOt^O OOOOOO'-'OOi-iOOOOOOOOOOOOO •ti-ti-H-H-H-ti-H-H-H-H-li-H-H-H+l-H-H-H-H-H-H-H-H C0Ot^t^00t-t0r-C0£xM00C5Oi-0r>.OC0O-o OOOOOOOOOfHOOOOOOOOOOOOO -K-H-H-H-H-li-H-H-li-H-H-H-H-H-W-H-li-H-H-H-H-H-H OCOCOOOiOOOOOCOOOCCOOiOOCOCOXiOiOOifJCOtyD .-H CO "O h- O O O C: lO iM CI --I O CO CO GO -+* to •-' CI r- CO LO (M(NcolO^-c:o^'^~'■■Ol^^t— -^-^cDOCJOt--«3(M'-to OOOOOO'-iOO'- ■< Ol !M W W M >- o-to--ODiOCOOOO OTffMCOt^-fCOfNiOOCO'-'OOCOOO'— 'COCO-rfCOGOCl t^t^O'^i>ot-ooioococooot-'Or-coai'-->'-''-'ooooooO'-'ooo OOi-<0C^10'— "OOt— ■— icOOOOOOOOCO O-iO »o o •-< ^OCOiOCOh-0>0 0— '■MCl.-iw.-H-tHi-KMOCQOOCO OOOOOO'-'OOOOOOOOOOOOOOOO ■H-W-H-H-H-H-H-ti-H-H-ti-H-H-H-H-H-H-fl-H-H-H-H-W eOMicioooiQcoiOcoi.o>noo-?t1— O'^00OC:c0f-OtNOOC0"tJ<'H(N OO'-''-''-i(N'-i>-it-i(NC^(M>-i'-HtNNeiC0C0C0iMWN (N-^iCtOf-O'-'fNCO'rftDr-a? i-iiO00T-«'-irHi-'Wi-i(MCN(M(NiNtN(M >) >) >3 >)_>) >) >i MtCtDtrsrtCtCtDtCbCtOtEfcCMW'bO The Cakbon Dioxide of the Soil Air 361 TABLE 8. Cakbon Dioxide (Per Cent by Volume) Produced Appaeentlt by the Millet Crop, 191S. Determined by Subtracting the Amount op Carbon Dioxide IN the Bare Soil from That in the Cropped Soil Date of sampling July 8 July 11... July 15... July 18... July 22... July 25. . . July 29..., August 1. . August 5. . August 8. . August 12. August 14. August 15. August 16. August 17. August 19. August 21. August 22. August 23. August 24. August 26. August 27. August 28. Carbon dio.xide apparently pro- duced by millet crop in High CO2 soil (I) — +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +1 +0 +1 +1 +1 +1 +2 +2 +2 + 1 + 1 +1 .050±.O43 .018±.025 .017±.O36 .025±.064 .025±.032 .367±.0S6 .135±.101 .285±.067 .480±.O0S .552±.021 .937±.035 .133±.029 .979±.041 .115±.019 .348±.028 .372±.048 .573±.031 .210±.026 .107±.062 .200±.01S .677±-01S .510±.011 .555±.048 Low CO2 soil (11) — 0.005±.003 — 0.012±.007 +0.02o±.004 0.000±.015 +0.04o±.025 +0.013±.061 +0.0S8±.058 +0.218±.049 +0.375±.055 -|-0.708±.170 +0.558 ±.022 +0.920±.050 +0.S80±.024 +0.975±.O39 +1.205±.054 + 1.283±.044 + 1.518±.019 +2.067±.0oS +2.082±.O75 + 1.995±.O60 + 1.S07±.064 + 1.6S5±.077 + 1.610±.056 Difference (I-II) — 0.045±.043 +0.030±-028 —0. COS ±.036 4-0.025±.066 — 0.020±.041 +0.354±.106 +0.047±.116 +0.067±.0S2 +0.105 ±.0.55 ^0.156±.167 +0.379±.041 +0.213±.058 +0.103±.048 +0.140±.047 +0.143±.0G1 +0.0S9±.066 +0.055±.03o +0.143±.064 +0.025±.096 +0.205±.063 — 0.130±.067 — 0.175±.078 — 0.055±.074 362 H. W. TURPIN TABLE 9. Cakbon Dioxide (Per Cent by Volume) in Chopped and in TJnceopped Soil of Low Initial Carbon-Dioxide Content (Millet, 1918) Date of sampling July S . . . . July 11... July 15. . . July 18... July 22. . . July 25... July 29... August 1. . August 5. . August 8. . August 12. August 14. August 15. August 16. August 17. August 19. August 21. August 22. August 23. August 24. August 26. Tem- perature (centi- grade) 17.0° 21.5° 19.0° 30.0° 23.0° 30.0° 24.0° 30.0° 21.0° 35.0° 23.5° 28.0° 31.0° 32.0° 29.5° 26.5° 33.0° 33.0° 33.0° 34.0° 30.5° Atmos- pheric pressure (inches) 28.99 29.12 29.12 28.94 29.31 29.22 29.14 29.07 28.92 29.03 29.16 29.07 29.21 29.16 29.50 29.53 29.21 29.17 29.10 29.02 28.96 Carbon dioxide produced in Cropped soil (I) 0.210±.002 0.283±.001 0.358±.001 0.57S±.001 0.795±.014 0.908±.059 1.008±.054 0.798±.039 0.750±.052 1.62S±.161 1.223±.018 1.710±.O43 1.405±.012 1.480 ±.033 1.683±.049 1.683±.042 1.94S±.016 2.655±.055 2.715±.074 2.690±.060 2.275±.064 Uncropped soil (11) 0.215±.002 .007 .004 0.295± 0.333± 0.578±.001 0.750±.021 0.895±.017 0.920±.021 0.5S0±.029 0.375±.017 0.920±.036 0.665±.012 0.790±.026 0.525±.021 0.505±.021 0.478±.023 0.400±.014 0.430±.010 0.588±.018 0.633±.014 0.695±.007 0.468±.006 Difference (I-II) — 0.005±.003 — 0.012±.007 -|-0.025±.004 0.000±.016 4-0.045±.025 -|-0.013±.061 +0.088±.058 -1-0,218±.049 -|-0.375±.055 -|-0.7O8±.17O -|-0.558±.022 -f-0.920±.050 -|-0.880±.024 +0.975±.039 -H.205±.054 -M.2S3±.004 -|-1.518±.019 -|-2.067±.058 -|-2.0S2±.075 -|-1.995±.060 -|-1.807±.064 Memoir 29, The Lecithin Content of Butter and Its Possible Relationship to the Fishy Flavor, the third pre- ceding aumber in ttiis series of publications, was mailed on December 23, 1919. I LIBRARY OF CONGRESS e 002 683 250