STUDIES IN THE DRYING OF SOILS i 594 K56 opy 1 A THESIS Presented to the Faculty of the Graduate School OF Cornell University for the degree of DOCTOR OF PHILOSOPHY BY MILLARD ALSCHULER KLEIN Reprinted from Journal of the American Society of Agronomy, Vol. 7, No. 2, March-April, 1915. In exchange JUK ^8 '^^ Jv^^ f o ^1 ti^^Reprinted from Journal of the American Society of Agronomy, Vol. 7, No. 2, 1915 i STUDIES IN THE DRYING OF SOILS.^ Millard A. Klein, Cornell University, Ithaca, N. Y. (Contribution from the Department of Soil Technology, Cornell University.) CONTEXTS. Page Introduction 50 Reviev\^ of Literature .■« 50 Experiment i, the Effect of Previous Drying of the Soil to Different Moisture Contents on Plant Food in the Soil and Plant Growth 54 Soils Used 54 Method of Experimentation 55 Effect of Previous Moisture Content on Plant Growth . . . . 56 Eft'ect of the Previous Moisture Content on the Morphological Char- acters of Wheat ; 56 Effect of Previous Moisture Content on Crop Yield 5'"^ Eff'ect of Previous Moisture Content on Total Nitrogen in the Crop ... 60 Eft'ect of Previous Moisture Content on Certain Constituents in the Water Soluble Matter in the Soil 61 Total Solids 61 Nitrates 62 Potassium, Calcium, and Phosphorus 64 Lime Requirements 66 Summary 66 Experiment 2, the Effect of Drying a Soil on its Physiological Con- dition as Measured by the Carbon Dioxid Production and Nitri- fication 67 Carbon Dioxid Produced on Drying and Wetting a Soil 67 The Effect of Drying and Wetting a Soil on the Nitrates and Nitri- fying Power 69 Summary 7 ' Discussion and Conclusions 72 Bibliography 75 1 A thesis submitted to the faculty of the Graduate School of Cornell Univer- sity in partial fulfillment of the requirements for the degree of Doctor of Phi- losophy by Millard Alschuler Klein, B.Sc. Ithaca, N. Y-., February, 1915. Re- ceived for publication March 2, 191 5. 49 50 jourxat. of the american sociktv of agronomy. Introduction. The drying of tlic soil by exposure to intense sunlight fc^ some timt has been made use of in certain arid regions of India to increase its productiveness. Since the drying of the soil in an arid region has a stimulating effect on crop growth, it is to be expected that the lower- ing of the moisture content in soils of the more humid regions, during seasonable changes, will influence their ])roductiveness. The drying of tlie soil is a process that depends entirely on the climatic conditions, the degree and duration depending on the amomit and distribution of the rainfall in the region concerned. In a study of the increased pro- ductiveness due to drying it will be necessary to consider the changes in the physical, chemical, and biological conditions of the soil. The change in the ])lnsical condition of the soil due to drying may be^easily olxserved in the field. A better tilth is obtained as shown by an increased granulation. This increased granulation is to a great ex- tent due to the Hocculation of the colloidal material. The changes in the chemical composition due to drying have been studied by many investigators in relation to the amount of plant food recox'erable when a sample has lieen previously dried, untler various conditions and temperatures. Great differences in the amount of plant food recovered have been observed when a samj^le has been previously dried, which would show that the dr_\ing of the soil in the field may greatly influence the chemical com])osition. In the last decade much attention has Ijcen given to the biological changes which are taking place in the soil. Jn this C(jnnection drving has been considered as a l)artial sterilization, as the result:- liave lieen similar to those obtained from a ])artial sterilization witli steam or antiseptics. The great impo>rtance of the biological factors cannot be ignored in the stud)' of the ture content depend ui)on the amount and variation of the rainfall in the region concerned. In a humid region the period of drying is short and the moisture content to which the soil is dried is usually not \"er\- low. In an arid region the soil is sometimes air-dry or nearly so and remains dry for some length of time. AVith this in view tb.e plan of the experiment was to determine under controlletl condition^ tlie elTect of dr_\-uig the soil to dilTerent moisture conients on ])lant food in the soil and on plant growth. Soils Used. Two soils were used in the experiment, differing onl_\- iii organic matter. Soil No. i i-w a heavy clay loam known as Dunkirk clay loam. It contains comparatively little organic matter, but the fertility is good. Soil No. 2 is the samq type of soil, l)ut the organic matter had been greatly increased b}- ];)i!ing v.p timothy sod and allowing- it to KLEIN: STUDIES IN THE DRYING OF SOILS. 55 decompose. Some of the organic matter liad not entirely decomposed. This caused some difficulty in preparing the soil for the pots, as the uftdecomposed organic matter would tend to mass together. MctJwd of Ex pcvimcntation. The two soils were hrought in from the field December 9, 1911, thor- oughly mixed and put in 3-gallon pots. Each pot contained 1 1 kilo' grams of wet soil. A moisture determination was made at this time and the pots were brought to complete saturation (40 per cent). All pots were removed to the field-house January 11, 19 12. On Febru-ary 28, 1912, the pots were brought in from the field-house. While the pots- were in the field-house the soil was frozen and a number of them were broken. The remaining pots were then allowed to dry in the greenhouse until they reached their permanent moisture content, as shown in Table i. T.-^BCE I.— The Moisture Content of Pots Used in the Experiment. Soil No. I. Series i, Unplanted. Pot No. Si-ries 2, Planted at 21; Percent. Conierrt. Soil No. Series i, Uiiplanted, j .Moisture Pot No. Content. Series 2, Planted at 25 Percent. Mcjisture ot No. Content. Percent. Pcrccnl. Percent. 42 T 422 424 4^5 426 427 428 429 30 30 40T 403 408 411 412 430 415 416 417 41 8 419 420 30 30 30 447 448 449 450 4.St 4.S2 4. S3 454 45. S 45f) 457 458 459 460 40 40 Per cant 431 15 432 TS 433 I3 434 20 435 20 436 20 437 25 438 ■?5 439 25- 440 ,^0 44 T 30 442 30 443 40 444 40 44.5 ^ The pots of the highest water content were at saturation. In soil No. I the highest water content was at 35 percent, but ajter a few months the water stood on the surface of the soil and it becajiie neces- sary to drop this water content to 30 percent. Just the opposite con- dition was found in soil Xo. 2, and the highest water content of 35 percent was raised to 40 percent. The moisture content as showm tn Table i gives this corrected percentage for the pots kept at saturation. The pots were kept at the difl'erent moisture contents as shown in 56 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. Tabfe i until December 19, 1912. They were then divided in two series. One series was prepared for planting by bringing all pots to 25 percent moisture content, while the second series was kept bare at the ditterent moisture contents. The division of the pots in two series is shown in Tal)le i. On January 14, 1913, all pots of series i were planted to Galgalos wheat. Fort}' seeds were jdanted in each pot. A good germination was secm"ed and the seedlings were thinned to 12 plants. .,'Effcct of Previous Moisture Coufenf on Plant GroictJi. At all early stage soil No. i allowed a Ix'tter growth. On April 29, 1913, the pots that had been previously held at a high moisture con- tent showed a ])Oorer growth than tliose held at a low moisture con- tent.' At th.e lime of heading the plants in pots 440, 441, and 442 were 'much smaller than others of the same series. Un June 4, the plants in pots 437. 43S, and 439 were making the best growth. On Ala}- 22, it could l)e seen that the drying out of a soil to a low moisture content ])revious to planting was having a Ijeneficial eiTect on plant growth. In soil Xo. 2 the pots which had been held at 30 percent moisture content previous to planting showed a poorer growth than the ones ])reviously held at 40 percent. A more luxuriant growth was ol:)tained <.)n soil 2, the great dif- ference evidently being due to the greater amount of organic matter in soil No. 2 or to some factor depending upon the organic content. On June 17, the plants were fully headed but were not entirely ripe. It was necessary to harvest on this date, however, owing to attacks made upon the plants !))■ rodents in the greenhouse. The plants on soil No. I were somewhat nearer maturit\- than those on Soil No. 2. The plants from all pots were hung in the greenhouse and allowed to ripen completelw Alillet was immediately planted, but a very poor growth of the seedlings was obtained. It was therefore replaced by buckwheat. The pots containing soil No. i had become so compact that it was necessary to lower the water content from 25 percent to 22 percent. During the growth of the buckwheat little difference could be ob- served. It was evident that the' pots had reached a point where the previous moisture content had little eiTect. or that buckwheat was not appreciably affected by changes in the moisture coiitent. Effect of Pre7'ious Moisture Content on tJie Morp]ioJo(i\ of'JJlieat. A study of the eff'ect of drying a soil to different moisture contents on the morphology of wheat is shown in Table 2. The results with KLEIN : STUDIES IN THE DRYING OF SOILS. 57 soil No. I do not show a' great ditTerence in the first three water contents (15. -20, and 25 percent). A great decrease will be noted in pots 418, 419, and 420 in the nunil)er of culms per pot, but only a slight difference in the other characters. These pots were held at saturation before planting and a poor physical condition of the soil was notic&able. Table 2. — Effect of Previous Moisture Content on the Morphological Characters of -Wheat, 1 P''^" 1: vious Pot No. I Moist- jUre Con- tent. Culms per pot (12 Prants). Length of Culm. Length of Head. per Head. Empty |,^P')^.t Spike "*" "" lets with one Grain. Spike- lets with Spike- I Nodes lets per t\^'° (Total.) Culm. Grains Soil No. I P. Cl. Inches Inches 401 15 25 34-7 3-08 16.8 2 8 7.2 4.8 — 4.0 403 15. 25 34 7 3.00 13-4 3 4 7.0 4 — 3-7 408 15 25 37 3 3-30 16.5 2 7 6.0 5 2 — 2,-?, Ave. 15 25 35 6 3-12 16.0 3 6.7 4 7 14.4 3-7 -411 20 26 33 5, . 3.20 15-4 2 3 7-1 4 2 — 3-9 412 20 20 42 5 3.20 1.7-0 2 4 6.5 5 I — 4.0 430 20 26 36 6 3.20 16.3 3 I 7.0 4 8 — 3-9 Ave. 20 24 3-7 5 .3-20 16.0 2 6 6.8 4 7 14.1 3-9 415 25 25 34 8 2. So 14-7 2 5 7.0 4 I — 4.0 ■ 416 25 22 35 3 3.00 13-8 3 7-r 3 3 — 3.0 417 25 19 34 0- 2.80 . 13-0 3 7.0 3 2 3.6 Ave. 25 22 34 7 . 2.95 14.0 2 8 7.0 3 5 13-3 3-7 418 30- 12 31 3 2.40 I0-.5 3 3 6.3 2 — 4.0 419 30 13 34 5 2,50 12.0 2 Q 6.1 3 — 3-7 420 30. ^ 13 31 6 2.45 10.3 I 6 6.3 2 2 — 3-5 Ave. 30' ^ 13 35 8 - ■ 2.45_ • II. 2 5 6.2 2 4 II. I 3.7 Soil Nor 2 431 15 36, 30.5 • 3.36 19.0 2.6 5-4 ,6.4 — 34 432 15 34 30.3 3-56 18.3 2.4 6 6.3 — 3 5 433 IS 44 34-4 ■ 3-40 17.0 2.5 5 3 • 5-8 — 3 5 Ave. 15 38 . - 31-7 3-40 18. 1 2-5 5 6 6.2 14-3 3 5 434 20 30 28.5 3-20 14.1 2:2 5 2 6.0 — 3 7 435 20 34 29.(1 ■ 3-20 16.8 2.2 5 5 5-5 ■ — 3 5 4J6 •20 34 30.0 3.60 16.9 2.0 5 7.3^ — 3 5 Ave. 20 33 29.4 3-30 ' . 15-9 2.1 5 2 6.3 13.6 3 6 437 25 33 32.4 3.60 . 18.6 2.0 5 2 6.6 — 3 7 438. 25 35 30.6 3-40 18.5 2.0 6 6.3 ■ — 3 6 439 25 27 34-3 ■ 3-40 - 16.6 1-7 5 2 0.5 • — 3 9 Ave. 25 . 32" 32.4 , 3--50 i7;-9 1.9 5 5 6.5 13-9 • 3 7 440 30 17 34,2 . 5-40 17-7 2.1 4 6.7- — . 3 6 441 , 30 17 23.2 2.50 13.0 2.3 4 4 ■ 4.4 — 3 2 - 442 k30 13 S2.^ .2:30 • 9.0 _3-5 5 2.0 — 3 Ave. 30 16 26.7 2.70 , 13-2 2.6 4 5 4-4 II-5 3 3 • 443 40 34 27.7 3.00 14-5 •2.4 6 5 4.0 — 3 3 .444 40 41 ■ 30.0 • ■ 3-10 i8.-f ?-7' 6 2 • 6.0 — 3 7 445 40 41 30.3 3-40 16.8 3-2 6 2 5-2 — 3 5 Ave. 40 ' 38 29-3' 3-20 16.8" 2.8 6 3 5-1 14.2 3 5 1 Also 5 three-grained spikelets. ■ - Also 7 three-grained spikelets. 58 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. Ill soil No. 2, gTcater (iitferences in the nioi'phological cliaractcrs due to tlie eflecl: oi the previous uioisture content could be noted. Here, as in the plant growth, tlie soil that had been held at 30 per- cent moisture content shows the poorest results. There is a similarity between the ])()ts which had been held at 15 percent and those at 40 percent, the average numl)ei" of culms per pot being as great in the 40 percent as in the 15 i)ercent pots. Comparing the two soils, we iiixt a greater number of culms per pot in soil No. 2, Init the length of culms is sonienvhat less in this soil. '^Jdie greater nunil)er of spikelets with one grain were found on the plants in soil No. i, and the greater number with two grains were found on the plants in soil No. 2. It will be seen that in soil No. i there was a decrease in the number of grains per head as the moisture content was increased, whila in soil No. 2 there was little diti'erence as aFfectetl by the ditTerent moisture contents. Rffcct' of J'l-crioiis Mcnshirc Cuiitciit o)i Crof^ Yield. A large nunil)er of investigators have studied the effect of ditTerent moisture contents on croj) yieUL '.riiey do uo[, however, consider the possil.)le iniluence of the moisture condition of the soil before planting. ]n this in\-estigation the soil A\'as kept at the different moisture con- tents for ten months l)efore ])Ianting. At the time of i)lanting all pots were brought to an optimum water conttnit and the weights recorded. During plant growth the ])ots were kept at tlvis content by adding dis- tilled water e\ery day and bringing the pots to standard weight, Lnder this jjlan an)- ditlercnces in the ajnount of dry matter produced in the crop nuist l)e due to the. effect of the previous moisture con- tent and not to differences during the gTowth of the plants. As the two soils differ only in organic content, a comiiarison'of the results should show the inliuence of organic matter on the factors eflecting tlie previous drying out o-f a soil io various moistrtre contents. The ehcct ot the previous condition* of soil moislui'e on tire produc- tiim 01 iuy matter is shown in Table 3. In soil No. I, the greatest weig-ht of dry matter in the first c.rojD, botii grain and straw", is foiuKl in the -'^oil that bad l)ecn pre.viou,s!y dried to 15 ])ercen!., a somewhat: snialler yiekl at 20 percent and at 2^, ])ercent. an<.l a decided decrease at 30 pcrcejit. The sail that w'as held at 30 percent was reduced to 25 percinifat the time of jdantrng". The same order of dilTereiices was fomid in soil No. 2, cxce]5t that when 40 percent is re^ached there is a decided iticr.ease over the 30 ])crcent. In this series the .soil that was held' at 40 percent was re- duced io J5 pci-ccnt at the time of drying. KLEIN: STUDIES IX THE DRYINC OF SOILS. 59 111 soil No. 2, a moisture content of 40 percent must be compared to the content of 30 percent in soil No. i, as in both cases we have complete saturation for each soil. In the clay loani pots which had been previously held at saturation the yield of dry matter is smallest, but in the organic clay loam pais which had been held at saturation the yield is as large as those with the lowest moisture content. If we consider that the lowering ot the moisture content in the pots at 40 percent moisture content is an effective drying out previous to planting, there is decided increase due to drying just before planting. T.\BLE s.—EjJccl of Previous Moisture Cotitcni on Weight of Dry Matter of Wheat and Buekn'Iieat Frodueed. SoR-No. I. Previ- ous Soil No. : Wh eyt. Previ- ous Wheat. Pot No. Mois ture ]!ucl:- uheat. Pot No. Mois- ture wheat. CoB- ttnt. Grain. Straw. ("on- tem. ( Irainr. Straw. P. a. Grams drains Grams P. a. Grams Grants Grams 401 15 IS. 2 30.3 5-9 431 15 20.5 42.3 _ 8.8 403 ^ 15 17-4 2S.7 4.5 432 15 17.0 39.0 9.0 408 15 ig.i 31.8 4-7 433 15 23.2 45-7 9.4 Ave. 15 18.2 30-3 4-7 Ave. 15 20.2 42.3 9.1 411 - 20 18.5 29 -.1 4-5 434 20 15-8 30.6 9.0 412 20 15-8 26.6 4.9 435 2a 16.3 34-5 9.6 430 20 20.0 33-2 4.0 436 20 21.7 42.5 9-5 Ave. 20 18 I 29. 8 4-5 Ave. 20 17.8 '35-9 9-3 41S 25 16.6 27.0 4.0 437 25 15.8 41-9 9.9 416 25 1 3 25.1 4.0 438 25 x6.S 40.1 10.8 417 25 11.4 20.6 5-.S 439 25 14-4 33-9 9.2 Ave. 25 14.0 24-3 4-5 Ave. 25 15-5 38.6 9-9 4-1 8 30 4.9 1 0.0 — . 440' 30 8.8 22.1 8.0 419 30 5.2 12.5 (X.2 441 ->" S-~ 11-3 7-4 4 2 a. 30 6-3 " r2.7 0.3 442 30 2.4 1-1 7.2 Ave. 30 .>-5 II. 7 ^i-3 Ave. 30 5-5 13-7 7-5 443 40 14.6 28.6 9.0 4-44 40 22.9 46-5 10. 445 40 20.2 41.0 10.8 Ave. 4Q 19.3 38.6 9-9 This, however, is not the case in the 30 percent moisture content pots which have alscr been lowered to 25 percent before planting. The eiTect of drying to lower moisture contents previous to planting has been to increase the crop yield, as is conclusively shou-n in soil No. I and also in sorl No. 2, if the lowering of the 40 percent moisture content l^efofe planting \yc so considered. With the second crop, Inickwheat, there has been little effect. There 6o TOI'RX-\L OF THE AMERICAX SOCIETY OF AGRONOMY. h, however, a greater increase in the yield of soil No. 2 over soil No. I than in the first crop. Effect of l^rcz'ioiis Moisture Content on tJic Total Nitrogen in the Crop. The results ol)tainecl in the determination of the total nitrogen in the dry matter of the grain and straw are shown in Table 4. It has been repeatedly shown that plants grown under different moisture condi- tions show a variation in the amotmt of plant constituents found in the dry matter. A greater crop growth usually causes a smaller percent- age of nitrogen in tlie i)lant. (hi the other hand, if the available nitrogen in the soil is increased l)y an increase in the moisture con- tent, an increase may be found in the percentage ()f nitrogen in the crop. The chemical constituti(3n of the soil niust be a factor, more 'especially in the soluble organic matter. Table 4. — Effect of Previous Moisture Coutcut 011 Total Nitrogen in the Crop. Soil No. I. Soil No. 2. w^ Total Nitrogen. .2 „• Total Nitrogen. y. -1 Wheat. Buckwheat. y. 3* ^ e5 il Wheat. Buckwheat. ~ 5 1' i ^ i Total. Ratio. - f 'J > 'J c Raiio. Straw. Rati,>. j • - 1 .5 Per- Pa- Per- Per- Per- Per- Per-\ Per- cent. cent, cent. cent. cent. cent. cent: cent. 401 15 1.40 — .27 — 1.63 — 431 15 3.26 — 1.02 — • 2.07. — 403 15 1.68 — .26 — 1.62 — 432 15 3-30 • — 1 . 1 3 ■ — ■ 2.25 — 408 15 1.60 — .25 — — — 433 15 3.26 — I . I S — 1.84 — Ave. IS 1. 59 100 .26 100 1.63 100 Ave. 15 3-27 100 I. II 100 2.05 100 411 20 1.73 — .26 — 1.74 — 434 20 3-24 — 1. 17 ' — 2.:50" 412 20 1.60 — .26 — 1.82 — 435 20 3.25 — 1. 16 — 2.10 — 430 20 1.48 — .29 — 1. 81 — 436 20 3.26 — .95 — 2.04 — Ave. 20 1.60 100 .27 103 1.79 109 Ave. 20 3-25 99 1.09 98 1 2. 15 104 41S 25 1.6^ — .26 — — — . 437 25 ,3-32 — ;i.i5 — 2.09 416 25 1.67 — .25 ^- 1-45 — 438 25 .? • 2 7 — 1.18' — 2.15 — 417 25 1.72 — .27 — 1.62 — 439 25 3-43 — 1. 12 — 2.18 Ave. 25 1.67 104 .26 100 1-53 94 Ave. 25 3-34 102 I. IS 103 2.14 104 418 .30 1.88 — .30 — 1.66 ■ — 440 30 3.06 — Leo — . 2.35 — 419 30 I-7I — -39 — — — 441 30 2.88 — ■1.60 — 2.40 420 30 t.53 — .28 — 1. 7 1 — 442 30 3.26 — 1.60 ;— 2.42 — Ave. 30 1. 71, 107 .32 107 1. 68 103 Ave. ■ 30 3-07 93 .1.60 '' 145 ; 2.39 116 443 40 3.36 — 1.25 ! — I 2.22 — 1 ■ ■ 444 40 3.3 1 1 — .88, — •i.5fi. — ^ 445 40 3.34 ■— .92 J, — 1.4') — 1 Ave. 4'J 3.34 102 1. 01 91 t.4() 71 KLEIN: STUDIES IN THE DRYING OF SOILS. 6 1 The results presented in Table 4 showthat there has been no effect on the nitrogen of the crop resulting from a dift'erence of the previous moisture content. A comparison of the two soils shows on the aver- age twice as much nitrogen in tlie plants grown in the soil high in organic matter as in the same soil low in organic content. As these soils differ only in organic content and the results sliow practically no difference due to water content, the dift'erence in the percentage of nitrogen in the dry matter must be caused through some factor due to the organic matter. Effect of Previous Moisture Content on U'ater Soluble Matter. It has been shown by a numljer of investigators that the complete drying of the soil causes an increase in the soluble salts recoverable from a water extract. However, in this investigation the soil has in no case been dried to an air-dry condition. The results presented in Table 3 show that a lowering of the mois- ture content previous to planting has caused an increase in the plant growth. In order to determine whether this increase was related to an increased amount of plant food, determinations were made on the total solids, nitrates, potassium, and calcium in the water extract and phosphorus in a fifth-normal acid extract. It might be expected that the greater plant growth in the soil high in organic matter would result from the large amount of plant food carried in the organic material. Water extracts were made from soils from all the pots immediately after the second crop was har- vested, by adding 500 c.c. of distilled water to 100 grams of the soil and filtering through a Pasteur-Chamberlain water filter. Total Solids.- — Tal)le 5 shows the results obtained in the determina- tion of the total solids frOm a water extraction of the soil sample. It will be seen from this table that low water content reduces the total solids in the unplanted clay loam, while in the planted series of this soil there is little dift'erence in the results. The results with the soil high in organic matter show an increase in the total solids in both the planted and unplanted series with an increased moisture content. Considering the effect upon the clay loam, it is evident that drying the soil to a lower moisture content has increased the water-soluble matter. The planted series of this soil shows this same increase, although at the time of planting all pots were brought to the same moisture content. The opposite eft'ect in the organic clay loam must be attributed to the greater amount of organic matter. It is evident that the lowering of the moisture content has had no effect on the total solids recovered, as the amounts increase with ' the increased water content. 62 TOfRNAL OF THE AMERICAN S0CT1<:TV OF AC.RONOMY. Table 5. — Rffcct of Prcrious Moisture Content on Solulilr Salts in the Soil (Total Solids in Water Extract Expressed in Parts per Million). Soil No. I. Series i. I'lantcd. Series 2, Fnplanted. o'-" Serii-s I, Planted. Series 2. Unplanted 401 i.S 390 ■ — 403 i.S 305 — 421 1.5 408 I.S 402 — 422 15 Ave. 15 ^3b 100 Ave. 15 411 20 408 — 412 20 37-' — 424 20 4.-?o 20 440 — 425 20 Ave. 20 406 120 Ave. 20 41. T 2.S 329 -- 410 2$ 344 — 426 25 417 ~5 — — 427 25 Ave. 25 3.1^^ 91 Ave. 25 418 30 366 419 30 362 428 30 420 30 320 ■ — 429 30 Ave. 30 350 95 Ave. 30 94 874 800 837 890 690 790 666 464 5f'5 523 — S26 — 525 6: 43 T 432 433 Ave. 434 435 436 Ave. 437 438 439 Ave. J . c J^ -ii 3 XI << i •- z .« 2i " =•3 ■s. ■= Z y f: ■5 ■> V « P-, > ^ '~ Oh " 15 517 — 447 15 1226 — 15 704 — 44S 15 747 — 15 43« — 449 IS 1510 — 15 553 100 Ave. IS 1198 100 20 915 _ 20 687 — 451 20 882 — ■ 20 473 — 452 20 2222 — 20 691 124 Ave. 20 155" 13 1 7O0 — 453 25 1613 — 870 — 454 25 1584' — 746 — 455 25 13231 — 792 j 143 Ave. 25 15071 127 440 , 30 941 — 456 I 30 1456 441 30 960 I — 457 ' 30 I3<''4 j^.\2 30 605 — 458 I 30 12352 A\-e. 30 835 151 Ave. 30 1724: 146 443 4» 741 ; — 459 ' 40 24501 — 445 40 938 ! — 460 40 1467' — Ave. 40 863 \ 156 Av. 40 '180S 153 It would seem lliat ihe loweriiit,^ of the water eontent as affecting the \vater-soliil)le jna.tter depends entirel}' u])(>n tlie t_\i)es of soil used. X It rates. — In order to ascertain what effect the lowei'ing of the nioi-ture content may ha\e upon the nitrification in the soil, the nitrates were determined on sami)les from all the pots after the second crop had heen har\-ested. The sami)!es were brought to the laboratory and the moisture and nitrate determinations were made within sixteen hours after sam])ling. The nitrates were determined colorimetrically by the phenol disnlphouic-acid method. The results are presented in 'J"able 6. If a com])arison of series i and 2 of both .soils is made it will be seen that a reduction of the nitrates was caused by ])lant growth. The ana.ly^es also show that the nitrate^ are le>s in the planted series of soil No. I than in the same series cif soil Xo. 2. d his may be due to the greater amount of nitrates present in the organic clay loam he- fore planting, there being more tlian necessary to satis f\' the require- KLEIN: STUDIF.S IN THE DRVINC, OF SOILS. •63 ments of the plants. From Tallies 3 and 4 it will be seen that a grealer growth and a greater amount of total nitrogen in the crop were obtained in the organic clay loam. A decrease -is found in the nitrates of the planted series due to the i)revi()us lowering of the moisture content, this decrease being more decisive in the clay loam. Under the unplanted series of both soils the results would tend to show that there has been little effect on the nitrates duo to a lowering of the moisture content. A reduction may be expected in the planted scries, as pots at the previous low moisture contents gave much greater growth. Table 6. — Effect of Previous Moisture Content on Nitrates in the Soil. 5oiI X >. I. ted. Soil No. 2. Series i. P anted Series 2. L nplan Se ries I, Planted. i s 'J y< " Ser es 2, L nplanted. Z i ^ ? 2 . Z p.p. 1 S: .2 2 § •h iA Previous Mni.sture Coiuent. Z ~ P.p.\ p.p. p.p. P.cl. m. p.cl. m. P.cl. m. P.ct. m. 401 15 14.0 — 421 ; 15 421 1 — 431 IS 1 204 , — 447 15 864I — 403 IS 22.0 — 422 15 183 1 - 432 IS 1 140 1 — 448 15 6881 — 408 15 21.3 — 433 IS ' no ; ^ 449 IS 502 — Ave. 15 19.0 100 Ave. 15 302 100 Ave. 15 151 100 Ave. 15 685 100 411 20 16.8 424 20 341 — 434 20 159 — 450 20 1647' — 412 20 26.4 • — 425 20 183 — 435 20 222 — 451 20 242 — 430 2D 54-9 — 436 20 186 — 452 20 801; — Ave. 20 32.7 173 Ave. 20 262 87 Ave. 20 182 132 Ave. 20 896 131 415 25 74-4 — 426 25 496 — 437 25 522 — 453 25 697 — 416 25 26.8 — 427 25 130 — 438 25 164 — 454 25 485 — 417 25 37-2 • — • 439 25 244 455 25 454 — Ave. 25 46.1 242 Ave. 25 313 103 Ave. 25 310 205 Ave. ^5 545, 80 418 30 78.0 — 428 : 30 767 — 440 30 405 — 456 30 560 — 419 30 61. 5 — 429 30 83 441 30 j 193 1 457 30 752! — 420 30 26.4 — 442 30 339 — 458 30 432; — Ave. 30 55-3 290 Ave. 30 429 134 Ave. 443 444 445 30 312 1 205 40 372 , — 40 - — 40 185 — Ave. 459 460 30 40 40 5811 85 760 — 752 — Ave. 40 278 184 Ave. 40 756 no Why the lowering of the moisture content in the unplanted series had no effect is hard to explain, as an aeration of the soil under the low water content would be expected to increase the nitrates, yet it is evident that the results are influenced by other factors which tend to equalize this eff'ect. It was thought that a study of the nitrate-producing power of the 64 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY, soil mig'ht throw some light on the effect of drying soil on the nitrify- ing organisms of the soil. At the time the nitrates were determined in the soil, another loo-gram sample was taken, placed in a bottle, plugged with cotton, and incubated for seven days at 30° C. Nitrate determinations were then made as shown in Table 7. A com])arison of the nitrates in the soil as shown in Table 6 with the nitrates after incubation as shown in Talile 7 will show that in nearly all cases denitritication has taken place. It can be seen from the tables that the variation in the samples from pots under the same treatment are too great to warrant any conclusions on the eft'ect of lowering the moisture content on the power of the nitrifying organisms of the soil. Table 7. — llffrcl of Prczioiis Moisture Coiitciif on Xitnitcs Produced by Incu- bation for Sci'cn Days at 5"° C. s .il No. I. g oil Nc . 2. Series i, Planted. Series 2. I nplanted. Series i, Planted. Series 2, Unplanted. 2 5 (^ A '> 1; ^ 6 CL, a Z a X 2, |'-3 c £ - " " Ch " — 1 P. P- P- P. p. p. p. p. p. p. P- P- Cl. m. cl. in. Ct. m. cl. in. 401 T5 30 — 421 15 240 — 431 15 124 — 447 15 433 — 403 15 04 — 422 15 — — • 432 15 144 — 448 15 (172 — 408 15 56 — 433 15 88 • — 449 15 672 — Ave. 15 53 1 00 Ave. 15 240 100 Ave. 15 118 100 Ave. 15 593 100 411 20 59 — 424 20 222 — ■ 434 20 264 — 450 20 1 152 — 412 20 48 — 425 20 184 — 435 20 170 — 451 20 370 — 430 20 34 — • 436 20 96 — • 452 20 704 — Ave. 20 47 89 Ave. 20 203 84 Ave. 20 178 153 Ave. 20 778 131 415 25 3 7 — 426 25 200 — 437 25 200 — 453 25 60S — 416 25 34 — 427 25 160 — 438 25 144 — 454 25 576 — 417 2S 40 — 439 25 168 — 455 25 336 — Ave. 25 3 7 70 Ave. 25 iSo 75 Ave. 25 171 145 Ave. 25 507 85 418 30 50 — 42S ' 30 21 — 440 30 352 — 456 30 480 — 419 30 34 — 429 30 84 — 441 30 7-^6 ; — 457 30 572 — 420 30 50 — 442 30 360 — 458 30 448 — Ave. 30 44 83 Ave. 30 52 20 Ave. 30 329 278 Ave. 30 500 84 443 40 144 — 459 40 528 — 444 40 — — 400 40 526 — i 445 40 152 — Ave. 40 148 125 Ave. 40 527 89 Pofassiiiiii, Cah'iitiii, and fliosfiJionis. — Determinations were made of the potassium and calcium in the water e.xtracts and of the phos- KLEIN : STUDIES IN THE DRYING OF SOILS. 65 Table 8. — Effect of Previous Moisiure Conient on the Fotassium, Calcium and Phosphorus in the Soil. Series i. Planted. Series 2, Unplanted. Pot Nc Previous ] Moisture Content. Ca. Pot. No. Previous Moisture Content. K. Ca. Lime P2O5. R.(Squired (CaO). Soil No. i • -. p. p.m. p. p.m. p. p.m. p. p.m. p. p.m. p. p.m. 401 15 42.2 9.0 421 IS 12.0 18.5 — 403 •IS 21.3 12.2 422 15 43-1 21.4 13.7 408 IS 12.6 10. 1 Ave. 15 23-3 10.4 Ave. 15 27-5 20.0 411 20 30.4 7-3 424 20 14.7 21. S — 412 20 21. 1 13.6 42s 20 41.8 25-4 I3-I * 430 20 II. 7 II. 8 Ave. 20 21. 1 10.9 Ave. 20 27.6 23-4 — 0) 415 25 21.3 9-7 ' 426 25 16.4 20.3 — 416 25 ■ II. 6 12. 1 427 ' 25 20.3 18.8 14.6 417 25 26.4 8.6 . , Ave. 25 19.8 10. 1 Ave. 25 18.3 19.6 — 418 30 24.4 — 428 1 30 12.7 22.0 — 419 30 21.4 14.6 429 30 32.3 12.6 15.0 420 30 22.2 8.4 Ave. 30 23-7 II. 4 Ave. 30 22.5 17-3 — Soil No. 2 431 15 28.3 I3-I 447 IS 74-4 23.2 14-3 1,400 432 15 19.2 17.6 448 15 84.2 27.1 — 433 15 62.2 9.9 449 15 60.0 29.6 — Ave. 15 36.6 13-5 Ave. 15 72.6 26.6 — — 434 20 38.4 19.0 450 20 144-3 32.7 13-4 1,100' 435 20 29.6 I5-I 451 20 84.4 18.6 — ■ — 436 20 34-3 14.6 452 20 55-8 32.3 — ■ — Ave. 20 34-1 16.2 Ave. 20 91-5 27.9 — — 437 25 14.6 17-3 ■453 25 104.0 27-5 18. 1 1.275 438 25 29.0 13-4 454 • 25 41.6 19.8 — ■ — 439 25 38.1 20.3 . 455 25 111.3 25.0 — — Ave. 25 27.2 17.0 Ave. 25 85.6 24.0 ■ — ■ — 440 30 45-2 21.0 456 30 112. 22.8 II. 8 1,200 441 30 61.0 17.2 457 30 61.8 25-9 — — 442 30 41.4 22.8 458 30 24.9 — — ■• Ave. 30 49.2 20.0 Ave. 30 86.9 24-5 — — ■ 443 40 22.9 19.4 459 40 96.6 24.8 15.2 1. 075 444 40 105.2 13-4 460 40 79.0 27.0 — • • -^ 445 40 9.2 12.3 Ave. 40 46.4 15.0 Ave. 40 87.8 25-9 phorus in a fifth-normal nitric acid extraction of the soils. The cal- cium was determined by the turbidity method and the potassium by the colorimetric method of the Bureau of Soils.'- The phosphorus 3 Schreiner, Oswald, and Failyer, George H., Colorimetric, Turbidity and Filtration Methods Used in Soil Investigations, U. S. Dept. Agr., Bur. Soils Bui. No. 31. 1906. 66 JOURXAT, OF THE AMERICAN SOCIETY OF AGRONOMY. was determined colurinietricall}' according to the metliod of Fraps.'* The results are sliown in Talkie 8. From a study of Table 8 it may be seen that there has been very little effect due to the different moisture contents. A reduction of the potassium and the calcium was found in the planted series of soil Xo. 2. The ])hosphorus was determined in the unplanted series of bodi soils and no differences were found due to differences of moisture content. It must l)e concluded from these data that the reduction of the 'moisture content has no ai)i)recial)le eff'ect on the potassium, calcium, ajid pho'sphorus in the soil. Lime Rcqnircnicut. — In order to determine whetlier the lowering of the moistm-e content hatl any effect on soil aciditv, lime re<|uirement deterniinaticms were made according to the metliod of liizzell.^ These results are presented in Table 8. The cla\- loam shows no lime re- quirement, the organic clay loam an average of i,200 p. p.m. CaO. No difjferences are shown i\uQ to the lowering of the moisture content. Sininiiary oj' ILvhrriiiicnt i. 1. The drying of soil prexious to planting has a Ijeneficial effect on plant growth. 2. The factor \\hich causes this bencticial condition due to drying is affected by the organic matter in the soil, as is shown from the results of the two soils used, which differ onl\' in organic content. 3. The j)revious dr_\ing of the soil has no eff'ect on the total nitrogen in the dry matter of the crop. 4. The \vater-solul)le matter is increased in the clay loam with a drying out of the soil, while in the same stjil with a high organic con- tent the opposite result occurs. The organic content nnist be the de- ciding factor. 5. In the planted series of l)Oth soils a decrease in the previous mois- ture content has re'"iS'ture .Moisture (]>,, ,, iC'ontent and i( onte]U and ^.f" ,?>'^' 1 'J'' me and IhenM-et 1 ^ct Four- (Put I). ^ iHeldforSiv;- HeldThiity- Eleyen Days ,^.^„ j) ' teen Days fiye Days (Pots). (Pot 6). (Pot 3). (Pot 4). Nitrates in the Soil Nitrif3ing Power after Inctibation for Seven Days at 30° C. Series i, Series 2, Series 3, Soil alone : 1 208 2 I 200 Ave. ' 204 Soil +2 gr. dried bl 1 192 2 lOo Ave. 176 Soil +0.5 gr. (NH4) 172 ood : 22S 200 214 2CO:!: 184 162 208 216 212 i3(' 136 136 336 304 368 384 376 400 400 400 I 140 143 117 166 264 328 2 160 133 117 166 2 5^J 336 Ave. 150 138 117 166 260 332 400 384 39-' 464 432 448 1 224 190 232 2S8 672 416 2 208 22S 224 304 640 416 Ave. 216 209 228 296 656 416 ]'"irst considcrini:^ the effects on tlie nitrates, we find that the (h\\Tng of the soil has greatly re(hice(l them, and as has lieen prev- ionsly shown also has rednced the car])on dioxid |)roduction. The revvetting of the dry soil for a period of sixteen days has fm'ther de- creased the nitiilication. in this sani])]e the opposite is found in the carhon dioxid production. In the soil held moist for thirty-tive da}S after one drying and in those previously dried twice and three times, ;m increase in nitrification is found. This increase corresponds with the carhon dioxid ])roduction in these samples. \\'hy samj^lc 3 has shown a decrease is not altogether clear. 'Jdie restdts from the nitrate determinations as compared with the carbon dioxid production show that the nitrification as effected hy the drying of the soil is for tlie mo^t ]>arl l.uological, hut there must he factors other than biological which inlluence this change. These will i)e discussed later. The nitrifying ])Ovver of the soil was determined in three series in order to obser\-e the effect of the addition of organic and inorganic KLEIN: STUDIES IN THE DRYING OF SOILS. J I nitrogen on nitrification. Samples of loo grams of soil were used in each cas^. The three series were as follows: Series i. Untreated. Series 2. 2 grams of dried l)lood added to the sample. Series 3. c.5 gram of (NHijSO^ added to the sample. It will be seen from Table 10 that the addition of nitrogen either in organic or inorganic form has increased the nitrification. However, the results from each treatment as compared with the nitrates before incubation show, in the main, the same order of difl:'erence. Considering the efi:'ect of drying of the soil on the nitrifying power, the original soil shows an increase of 54 p. p.m. when the soil has been incubated alone. Series 2 and 3 of the same sample gave an increase of 26 and 66 p. p.m. respectively. In the dry soil the nitrates are in- creased in about the same ratio, but here there is an error due to the wetting of the soil on incubation, and the same results are obtained as in sample 3. If the nitrifying power of the dry soil had been deter- mined, it is very proljable that no nitrifying power would have been obtained. In sample 3 there was an increase of 55, 95, and 11 1 p. p.m. in series i, 2, and 3 respectively. This shows that the effect of prev- iously drying a soil is tO' increase the activity of the nitrifying organisms. In sample 4 the incubation of the soil has shown a decrease, but an increase of 138 and 130 p. p.m. was found in series 2 and 3 of this sample. In the carbon dioxid determination the rewetting of the soil for a period of thirty-five days gave a result similar to the orig- inal soil. Soils dried two and three times have increased the nitrify- ing power over the samples dried once. From the table it can be seen that the maxinumi is reached at two dryings. These results would show that the activity of the nitrifying organisms is increased liy a previotis drying of the soil, Init reaches a maximum at two dryings. Sitniiiiarx of Experiment 2. 1. The bacterial activity as measured by the carI)on dioxid produc- tion is increased by a previous drying of the soil. 2. The carbon dioxid production is very low in a dr}- soil, the pro- duction ceasing after seven days. 3. The activity is increased by two dryings, the third drying show- ing only very slight increase over the second. 4. A soil held moist for thirty-five days after one drying assumes its normal condition, the activity being only slightly greater than in the original soil. 5. The previous drA'ing of the soil increases nitrification. ']2 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. 6. The dry soil shows a reduction in nitrates, as in the carbon dioxid ])roduction. 7. The nitrilication is increased by two dryings and again in the soil dried three times. 8. The nitrifying power ol the soil is increased by a previous drying. 9. The nitrifying power continues to increase witli two dryings, Init prblialjly reaches its maximum at three dryings. 10. The ettect of adding organic or inorganic nitrogen to the samples is shown by a marked increase in the nitrates produced. The increase in the determinations is in the same ratio as in the sample with no nitrogen added. • ■ - Discussion and Conclusions. The foregoing results show that the drying of soil has an effect on its fertility, which results in an increased plant growth. The crop growth is increased by a previous lowering of the moisture content, but the diiterence in the organic content as shown in the two soils used, has influenced the changes which are produced. In Experiment i there is a drying out of tlie soil by a lowering of tlie moisture content, but in no case do we have a soil completely air-dried. This experiment represents a condition that takes place in a humid region where the soil rarely reaches an air-dry condition. In a consideration of the results from Experiment i this must be kept in mind. While the effects of drying on the physical changes have not been delmitely studied, a discussion of the subject will necessarily include the ph}\sical factors which are acting through a change in the soil moisture. The drying out of the soil increases the granulation, which is in the most i)art due to an alteration of the colloidal material. The increased graiuilation allows a greater amount of soluble salts to be carried in the granules, which on subsecjuent wetting allows a greater amount to go into solution. Referring to the results obtained on the amounts of water soluble material found in the two soils under diiferent mois- ture contents, we find that the drying out of the clay loam has caused an increase in the water soluble material, while in the organic clay loam the opposite occurs. As these soils differ only in the organic contc-nt. the factor which influences the solubility of the soil constitu- ents nnist be due to the dift"erence in the organic matter of the two soils. If in the clay loam a granulation due to drying has caused a greater alteration of the colloidal material, this would allow the water greater access to the soil particle; and if the concentration of the salts KLEIN: STUDIES IN THE DRYING OF SOILS. 73 on the surface of the particle has resulted from an increased film ■pressure around the particle, a greater amount of soluble material will be recovered by a subseciuent wetting of the soil. However, in the organic clay" loam the decrease found in the soluble matter on drying would tend to show-that the great amount of material soluble when the soil is held at high water content overcomes any increase that may be due to a drying of the soil. Again, as the organic clay loam shows a lime requirement of 1,200 p.p;m. CaO, the acidity which is due to the organic matter would deflocculate the colloidal material, resulting in a less amount of surface being exposed to the solvent than in the clay loam. It has been shown by previous investigators that a soil high in organic matter has a great absorptive power. This ab.sorptive power would increase the plant food held by the soil and result in an increase of the soluble matter when the soil was dried; but if the soil was not dried to a low enough water content to alter this absorptive power, no increase would result'. The resinous and fatty material of the organic matter may surround the mineral particles anil allow no greater solubility even if more soluble salts are -exposed to the solvent after a drying of the soil. It has been considered by some investigators that the water-soluble material forms a colloidal film around the soil particle. On drying a soil this film will be altered and allow a greater solubility of the sol- uble salts. This may partly account for the increase in the water-soluble material in the clay loam when dried to a 15 percent moisture content, but in the organic clay loam it may be that the large amount of organic matter soluble would strengthen this colloidal film and a greater drying be necessary to alter the pressure of the film. Other factors, mainly chemical, must be considered in a discussion of the effects of drying soil. The dehydration of the silicates, deoxi- dation of the oxids, and oxidation of many of the compounds are some of the important chemical changes which take place in the soil on drying. However, in Experiment i the soil has not been dried below a moisture content of 15 percent, and these factors cannot exert any marked influence on the changes produced. The drying out of the soil causes an increase in the nitrification in the planted series, but no efi'ect is observed in the unplanted series. Why this occurred is not clear. The biological factors that are at work here may sufficiently alter the results so as to eliminate any diiference due to the changes in moisture. This will be discussed further under the results of Experiment 2. Turning to the determinations of potassium, calcium, and phos- phorus, as afl:'ected by the lowering of the moisture content, it was 74 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. found that there is no increased solubihty of these elements. This would show that the beneficial eifect on plant growth must be due to a great extent to an alteration of the ])hysical condition of the soil and not to a greater amount of plant food being liberated. 'J1ie results from Experiment i show that the lowering" of the moisture content ]>revious to planting has a beneficial efi:'ect on plant growth. ( )f the changes produced in the soil, tlie physical, chemical, and l)iological factors nnist be considered, but in the results obtained from Ex])eriment i, it would seem that the change in the physical con- dition is the iM"incipal factor. In Experiment 2, iItc results of drying a soil are studied in connec- tion with the l)ioIogical changes. The eilects on the biological factors have been measured by the l)iochemical changes produced. This ex- periment difil'ers from ]^xi)eriment i in that the soil was dried in a tlry- ing room at a temperature (')f 30° C. and ma_\" be considered as air- dried. T>efore discussing the eftects of drying on the [jhysiological changes produced as measured !»>■ the carl)on diijxid production, it will be well to consider whether the carbon dioxid produced is a correct measiu'e of the I)acterial activity. The most important objection to this method is that the amount ol)tained in some cases a])pears to be too high to attri])ute to bacterial action. The chemical changes produced on dry- ing may be partlv res])onsil)le for the increase in carljon dio.xid. It can not l)e s.aid that all the organisms in the soil evolve carbon dioxid: ])ut if the most important soil organisms produce carbon dioxid and if the changes jirodnced 1)\' dr\ing act similarly on these organisms, the measuring of tlie carlion dioxid ])roduction should give a relative measurement of the ])aclerial activit\. The results of the experiment show that a prex'iously dried soil gives a greater bacteri.al activity as measured b)- the carbon dioxid production and nitrification in the soil. There are a number of pos- sible reasons to be considered in a discu-sion of the efi:'ect of drying on the i)hysiological condition of the soil. It has ])een shown l)y mrmy investigators that the organisms in the soil. excei)t the nitrificrs, ;ire resistant to drying. If the nitrifying organisms are destro\ed on drying the soil, then the increased nitrifi- cation must l)e accounted for through chemical changes produced in the soil. The drying of the soil alters the colloidal material and allows a greater amount of oxygen to enter the soil. After the soil has been wet again an increa.-e is found in the nitrates, which would lie due to the induced oxidatirtn. 1 1 in drying a soil a greater .amount of |)laiU food is made available, KLEIN: STUDIES IN THE DRYING OF SOILS. 75 the bacteria would be able to obtain a greater supply of food. Ac- cording to Greig-Smith, the drying of the soil would destroy the vva.xy substance surrounding the soil particle and allow the more re- sistant bacteria a greater food suppl} . The resistance of the organisms to drying may be due to the formation of spores. As it is known that the nitrifying bacteria do not produce spores, we may consider that the decrease in the nitrify- ing organisms and the increase of the other organisms on drying may be due to the ability of the latter to form spores, in a discussion of the causes of the beneficial efiect due to drying it is necessary to consider the h}pothesis of Russell and Hutchinson. Considering that the drying of the soil is a partial sterilization, they believe that the drying of soils destroys or inhibits the action of the phagocytic or- ganisms, and an increase in the ammonifying bacteria results, which is beneficial to the productiveness of the soil. In an air-dried soil the hygroscopic water may be sufficient to satisfy the requirements of the bacteria. The hygroscopic water is held around the soil particle as a thin film. This film exerts a very great pressure, which, it seems, would not allow the organisms to obtain the water or the food enveloped in it ; but if the bacteria themselves were included within this film, then sufficient food might be obtained. From the results obtained in this investigation and by other workers it would seem that the increase in bacterial activity on drying a soil is not a question of bacterial numbers, l)Ut depends upon the relative resistance of the important soil organisms. In a consideration of the efifect of drying a soil on the physiological condition of the soil, no definite conclusions can be drawn until more knowledge is obtained relating to the eltect on the difi'erent groups of organisms. The sul^ject is very complex and must include many factors both chemical and physical, as. for example, an alteration of the colloidal material which would allow a greater oxidation. The results of these studies show that the drying of soil afl^ects the physical, chemical, and biological factors, resulting in an increased plant growth. The increased crop growth on a soil that has been previously dried is of importance to the practical (luestion of soil management, more especially in the arid regions where the soil is often air-dried. Bibliography. Cameron, F. K., and Gallagher, ¥. E. 1908. Moisture Content and Physical Condition of Soils. C. S. Dept. of Agr., Bur. of Soils Bui. 50: 7-70. 76 JOURNAL OF THE AMERICAN SOCIETY OF AGRONOMY. Fippin, E. O. lOio. Some Causes of Soil Granulation. Proc. Amer. Soc. of Agron., 2: 106-121. Fisclicr, Hugo. 1012. \'om Trocknen dcs Bodens. Ccntbl. Bakt. II: 36: 346-340. Circis-.Smitii. igii. The Bactcriotoxin.s and Agriccre of Soils. Centbl. Bakt. II: 30: 1 54- 1 :S. Howard, A., and Howard, G. L. C. 1007. The Fertilizing Effect of Sunlight. Nature (London), 82: 2103:456. Kelley, \\'. P.. and McGeorgc, W. 1013. The Eft'ect of Heat on Hawaiian Soils. Hawaii Agr. Expt. Sta. Bui. 30 : 5-38. King, F. H. 1905. Investigations in Soil Management. V. S. Dept. of Agr., Bur. of Soils Bui. 26: 13-205. Leather, J. \\\ 1912. Records of Drainage in India. Mem. of the Dept. of Agr. in India, 2 : 63-140. Lyrtn, T. "L., and Bizzell, J. A. 1013. Some Relations of Certain Higher Plants to the Formation of Ni- trates in the Soils. Cornell Univ. Agr. Expt. Sta. Mem. i : 9-1 11. Pickering, .S. U. 1908. Studies nn ( iermiriation and Plant Growth. Jour. Agr. Sci. 2; 4II-43-1- 1908. The Action of Heat and .Antiseptics on Soils. Jour. Agr. Sci. 3: 33-54- Rahn, Otto. 11)07. P.akteriologische Untersuclnmgen liher das Trocknen des Bodens. Centlil. Hakt. II : 20: 3S-61. Richter, L. 1806. UI)cr die Ver;inderung whelche der Boden (lurch der Sterilisieren erleidt't. Landw. \'ers. Stat. 47: 26i>-274. Kitter, G. W. 1912. Das Trocknen der Erdcn. Centlil. Bakt. II: 3,}: 116-143- Russell, E. J. 1910. The Fertilizing Effect of Sunlight. Nature (London), 83: 2105: 6. Russell, E. J., and Hutchinson, H; B. 1909. The Fff(-ct of Partial Sterilization of Soil on the Production of Plant F.iod. J(_)ur. Agr. Sci. 3: 111-144. 1913. Ibid. Jour. Agr. Sci. 5: 152-221. Russell, E. J., and Petherhridge, F. R. 1913. On the Grijwtii of Plants in Partially Sterilized Soils. Jour. Agr. Sci. 5: 248-2^7- Russell, E. J., and Smith, N. 1905. On the Question whether Nitrites or Nitrates are Produced by Non- liacterial Processes in the S(^il. Jour. Agr. Sci. i: 444-453. Sharp, L. T. 1913. Some Bacteriological Studies of Old Soils. The Plant World, 16: loi-l 15. KLEIN: STUDIES IN THE DRYING OF SOILS. 7/ Warrington, R. 1882. Determination of Nitric Acid in Soils. Jour. Chem. Soc. Trans., 1882: 351. Wollny, E. 1897. Untersuchungcn iil^er der Volumveninderungcn dcr Bodenarten. Forsch. auf d. Geb. Agr.-Pliys., 20: 2: 14. Acknowledgment. The writer desires to acknowledge his profound gratitude to Pro- fessor T. L. Lyon, under whose inspiration and direction these results have been accomplished; also to Professor W. A. Stocking, Jr., for valuable assistance in connection with the bacteriological methods used. LIBRARY OF CONGRESS 002 672 648 7