S che a) KS U.S. DEPARTMENT OF AGRICULTURE. BUREAU OF PLANT INDUSTRY—BULLETIN NO, 211. i 2 B. T. GALLOWAY, Chief of Bureau, BACTERIOLOGICAL STUDIES OF THE SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. BY . ; KARL F, KELLERMAN, = —. Physiologist in Charge of Soil-Bacteriology and Water-Purification Investigations, AND E. R. ALLEN, Scientific Assistant. Issuep Aprit 15, 1911. oa ea WASHINGTON: “GOVERNMENT PRINTING OFFICE. * POEL, oh y Aw 4 4 hall : i AG lap “9 ‘ 4 hy , aoe Eeye “ys ‘Oye aa! 5 sal Woe OP PARIT MENT GF AGRICULTURE. BUREAU OF PLANT INDUSTRY—BULLETIN NO. 211. B. T. GALLOWAY, Chief of Bureau. BACTERIOLOGICAL STUDIES OF THE SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. BY KARL F. KELLERMAN, Physiologist in Charge of Soil-Bacteriology and Water-Purification Investigations, AND E. R. ALLEN, Scientific Assistant. IssuEpD AprRiL 15, 1911. WASHINGTON: GOVERNMENT PRINTING OFFICE. Load. on ca BUREAU OF PLANT INDUSTRY. Chief of Bureau, BEVERLY T. GALLOWAY. Assistant Chief of Bureau, WILLIAM A. TAYLOR. Editor, J. E. ROCKWELL. Chief Clerk, JAMES E. JONES. SoIL-BACTERIOLOGY AND WATER-PURIFICATION INVESTIGATIONS. SCIENTIFIC STAFF. Karl F. Kellerman, Physiologist in Charge. T. R. Robinson, Assistant Physiologist. I. G. McBeth, E. R. Allen, R. C. Wright, and Edna H. Fawcett, Scientific Assistants. F. L. Goll and L. T. Leonard, Laboratory Aids. 211 2 LETTER OF TRANSMITTAL. U.S. DEPARTMENT OF AGRICULTURE, Bureau oF Piant Inpustry, OFFICE OF THE CHIEF, Washington, D. C., January 17, 1911. Sir: [ have the honor to transmit herewith a paper entitled “‘ Bac- teriological Studies of the Soils of the Truckee-Carson Irrigation Project” and to recommend that it be published as Bulletin No. 211 of the series of this Bureau. These investigations, though in many ways of a preliminary char- acter, indicate some of the possibilities of a bacteriological diagnosis of soils and will be of interest to all-who have to deal with problems of soil fertility. Respectfully, Wm. A. TayLor, Acting Chief of Bureau. Hon. JAMES WILSON, Secretary of Agriculture. 211 3 ae os ‘ ¥ 7 He i a ‘ nen WAY A ss Li a a) > a. , ms ve er | ‘ at e Lett i iy it a r er net 77 kei ie + Saray ae CAN TENS: Page AHEM RNOR IS ce es. Aaa eias See iahe Soe dale Sheds Sohne RISES Ss caren eB tea i. « 7 Methods employed in bacteriological investigations of the soil at Fallon, Nev... 3) VEU MNeIMenTStOMMEMMEl Jase ace dee nee foe se aes ke See Ieee aad cir 8 ACCRUES META: Vie gc Suse SO. ee Awe Sagi: Gusnde Wee. we ts 9 PUM aM IGEN So a eee Hee aka pe cee a athe o oor eet - es 9 PENI ERNG, Oa yee AS A Se cis boot ASU Ouest Sv sem tUR ba ea deeeat Le 10 ME De NMA RTIARER ocd en AE a A, ae ek I ow 2 ee Ik tap MEET peer ee 11 Maa MEMEO, tee Aas oR Late ie & SS nce s Soon ABE ee GORE ee oe = 11 Niirityine power of soils at different depths. ........2.-2-.2..2s--0.-ecach:- 12 Nines non or.samiples in solutions. 2.0. ies see... eo. ac fae ee i lee. 19 Se lomimersna Swipes. se Sele Se eects Sek ees hotest IE ee 21 Pane Te EULER NE eo Ne tak Se fe ea Rytiaral s wre meio Ge AE Coe Se a ee Ba pene ate o 22 Relative numbers of bacteria in different soils..............--...------------ 24 Detailed study of soil typical of extensive areas..,.......--.2--222-----+2--- 25 SER HCESM MEISE UMN Terr eR rep Ne, SS) haan SUA Sion ee Oe SS bo wept getaere wees ale 32 Re eee ees 5 KS eos Se Se o's Sede TU ce See Uae aae gon uc thaine 35 ILLUSTRATIONS. Page. Fie. 1. Location of sampling plats in the experimental fields of the Truckee- Carson Experiment Farm, south of Fallon, Nev... figs 8 2. Diagram showing the stages ors of ammonium sulphate 7 in damyiles of soil from different depths from plats 100 and 110, Truckee-Carson PS WELMMGN HAM sac. so Foch men Sacha sain eames <5 cielo. pasar creel = 12 3. Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 120, Truckee-Carson Experiment LNCNE Da Eat My ie ES ap ay ik I a Te a ean ra PNP Re re, Ome, Sa 13 4, Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 130, Truckee-Carson Experiment Bites aerial eos hh ee ie a ees dais cite on. cb acencee e's Senate 13 5. Diagram showing tke nitrification of ammonium sulphate in samples of soil from different depths from plats 160 and 170, Truckee-Carson epGrURMe MME RIM grec erent aie ERs cee es wales dian aihiviw Sw ne ger i ee 14 6. Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 180 (poor soil) and plat 190 (good sGil); Meuckee-Carson Experiment Warm.....+-.--...--ogeiossien2s-2- 15 7. Diagram showing the nitrification of ammonium qn in samples of soil from different depths from plat 200, Truckee-Carson Experiment AE carseat ees ere oe ee heat cte anaes en Cras lore /ale Xero taloe io iso ele Naiererate Sie stz 16 8. Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 210, Truckee-Carson Experiment Fig. 9. 10. leis 13: A: 15. 16. 18. MS): ILLUSTRATIONS. Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 220, Truckee-Carson Experiment Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 230, Truckee-Carson Experiment BPARMD «uss Sta jane eases cle iter ears ee mPa OL Pe ed ce a Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plats 240 and 250, Truckee-Carson Experiment Narniso.- Se seer taae = sale Aare stan epee te ee epee eee 2. Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plats 260 and 270, Truckee-Carson Experiment, Marmo es. 4550 oh sso iat ees eet ae ete hee a Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plats 280 and 290, Truckee-Carson Experiment Warm so. JA 2h oe tee Oe epee sper ot ao ee ee ce Diagram showing the relation between the quantity of alkali and the nitrification in samples of soil from plats 180, 190, 170, 150, 100, 160, 110, and 120, Truckee-Carson Experiment Farm. Samples taken from-deépths of0\te,Ganches 2.25.0. 453 e ee oe ee ere ae ae Diagram showing the relation between the quantity of alkali and the nitrification in samples of soil from plats 180, 120, 170, 100, 190, 150, 160, and 110, Truckee-Carson Experiment Farm. Samples taken from Diagram showing the relation between the quantity of alkali and the nitrification in samples of soil from plats 180, 190, 170, 100, 120, 160, 110, and 150, Truckee-Carson Experiment Farm. Samples taken fronidepths ol 12 te lS mches Ys oe oo. ewan esos ad ele cease . Diagram showing the relation between the quantity of alkali and the nitrification in samples of soil from plats 180, 170, 190, 100, 110, 160, 150, and 120, Truckee-Carson Experiment Farm. Samples taken from depths'ot 8 to 24 im@hese -: hc. so sole eels on Stee wees Diagram showing the effect of calcium sulphate upon the nitrification of ammonium sulphate in samples of soil from plat 300, Truckee-Carson Experiment Farm, representing poor soil ‘‘A;’’ plat 310, representing poor soil ‘‘B;’’ and plat 320, representing good soil................- Diagram showing the ammonification of peptone in 7 days in samples of soil from plat 350 (good soil) and from plats 330 and 340 (poor soil), ‘Truckee-Carson Hxperunent: Harm: (00). ooo. ot ne as ote cl = senate . Diagram showing the ammonification of peptone in 15 days in samples of soil from plat 350 (good soil) and from plats 330 and 340 (poor soil), Truckes-Carson, Experiment Warm — pe fen)=. psa 2 = se ee 5 211 Page. 17 17 18 19 21 30 31 B. P. I.—646. BACTERIOLOGICAL STUDIES OF THE SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. INTRODUCTION. In making a bacteriological study of any soil or group of soils there are certain fairly well defined groups of micro-organisms whose func- tions, although as yet imperfectly understood, are recognized as im- portant factors in crop production and are more or less familiar to everyone who has attempted to investigate the problems of soil fertility. These groups of micro-organisms may be roughly separated into four classes, depending upon their physiologic characteristics: (1) Parasites, or organisms important chiefly because they are patho- genic to animals or plants and are frequently found in soils; (2) the cellulose-destroying organisms; (3) the organisms associated with the formation of humus; and (4) the organisms associated with the trans- formation of soil nitrogen. Only those groups concerned with the transformation of nitrogen, which in the form of ammonia or nitrate is practically the most important of all plant foods, are reported upon at this time. The data sought in studies of this character may be outlined as follows: (1) Total numbers of saprophytic bacteria in measured quantities of soil. (2) Ammonification; the breaking down of nitrogenous organic matter into ammonia. (3) Nitrification; the oxidation of various compounds of nitrogen to nitrate. (4) Denitrification; the reverse of nitrification. . (5) Nitrogen fixation, symbiotic and nonsymbiotic; the utilization of atmospheric nitrogen in forming nitrogenous organic compounds. In the work conducted at Fallon, Nev., during the season of 1909, in cooperation with the Office of Western Agricultural Extension, no quantitative study was made of nitrogen fixation, and the data on the subject of ammonification are very meager. Some preliminary inves- tigations in arid regions had shown that nitrification takes place here at considerable depth. All studies, therefore, were made of a 3-foot zone, keeping separate the samples of soils from different depths. The comparative nitrifying power of the different samples from the various plats is shown by curves, the parts per million of nitrogen as nitrate and nitrite being plotted as ordinates, and the different depths as abscisse. These curves show only the gain in nitric and nitrous nitrogen. Chlorids and sulphates are also shown, but seem to be of 211 7 8 SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. little importance. The quantity of nitric nitrogen originally present is shown in the legends under the diagrams (figs. 2-13). A description of the Truckee-Carson Experiment Farm, at Fallon, Nev., upon which practically all of the work herein reported was con- ducted, is given in a previous bulletin of this Bureau.!. The designa- tions of the small plats from which samples were taken for bacterio- logical study and their location are shown in figure 1. Fig, 1.—Location of sampling plats in the experimental fields of the Truckee-Carson Experiment Farm south of Fallon, Nev. METHODS EMPLOYED IN BACTERIOLOGICAL INVESTIGATIONS OF THE SOIL AT FALLON, NEV. REQUIREMENTS TO BE MET. Investigations in soil bacteriology require first of all the selection and development of satisfactory methods for determining the dis- tribution and activity of the micro-organisms which may occur under ' Scofield, ©. S., and Rogers, 8. J. The Truckee-Carson Experiment Farm. Bul- letin 157, Bureau cf Plant Industry, 1909. Atal METHODS EMPLOYED IN BACTERIOLOGICAL INVESTIGATIONS. 9 different soil conditions. Though it is recognized that the methods suggested by different investigators are not adequate for accurate quantitative investigations of bacterial functions and conditions in various soils, the methods which at this time have been found most convenient and suitable for the investigations under discussion are briefly reviewed. COUNTS OF BACTERIA. Samples of soil were collected with as strict aseptic precautions as it is possible to observe under field conditions. Sterile salt-mouth bottles were used as containers, and the soil auger used for taking up the soil was carefully cleaned and flamed over an alcohol lamp before sampling each stratum. In the laboratory 1-gram portions were removed from the bottles with a sterile scoop which held the required quantity, transferred to 300 cubic centimeters of sterile water in 500-cubic-centimeter flasks, and the whole shaken thoroughly at short intervals for fifteen minutes. One-cubic-centimeter portions of these infusions were then removed with sterile pipettes and added to 10 cubic centimeters of melted beef agar, and plates poured in the ordi- nary manner and incubated at 28°C. Counts of bacteria were made at the end of five-day periods. AMMONIFICATION, Sterile peptone solutions having the following composition were inoculated with 5 per cent of soil and the ammonia determined at the end of seven and fifteen days by distillation with magnesia: PCRS Serer teeter Mine ts, See er ee es ee 2 ate Ne 15 grams. Dipotassium phosphate.............- POE ES, SET! ee Tee 3 grams. Mee nentimimnlphate. Aon 5-6 265 Lud eg ahlk ie doe t eee.) @ oO ReMDS. RnnOrCMhiCiet. ee eae te cet e So 2 eave wh SS-, (pe OTOMS. NUE ISTES Say NE Cte Sa he a ne ae are seni| e011) Koma oe 1 Lipman, J.G. Experiments on the Transformation and Fixation of Nitrogen by Bacteria. Twenty-fourth Annual Report, New Jersey State Agricultural Experiment Stations, 1903, pp. 217-285. Lipman, J. G., and Brown, Percy E. Methods Concerning Ammonia Formation in Soils and Culture Solutions. Report, Soil Chemist and Bacteriologist, New Jersey Agricultural College Experiment Station, 1908, pp. 95-105. Lipman, J. G.,and Brown, Percy E. Noteson Methods and Culture Media. Report, Soil Chemist and Bacteriolégist, New Jersey Agricultural College Experiment Station, 1908, pp. 129-136. Lipman, J. G. Azotobacter Studies. Report, Soil Chemist and Bacteriologist, New Jersey Agricultural College Experiment Station, 1908, pp. 137-143. Léhnis, F. Ein Beitrag zur Methodik der bakteriologischen Bodenuntersuchung. Centralblatt fiir Bakteriologie, Parasitenkunde und Infektionskrankheiten, pt. 2, vol. 12, no. 6-8, pp. 262-267, June 24, 1904; no. 11-16, pp. 448-463, July 14, 1904; vol. 17, no. 14-16, pp. 518-528, December 7, 1906; vol. 20, no. 24-25, pp. 781-799, April 15, 1908; vol. 24, no. 5-7, pp. 183-192, August, 1909. Remy, Theodor. Bodenchemische und Bakteriologische Studien. Landwirt- schaftliche Jahrbiicher, vol. 35, Supplement 4, pp. 1-62. Berlin, 1906. 78011°—Bul. 211—11——2 10 SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. NITRIFICATION. Samples of soil were collected with the precautions previously described. In some cases 1-gram portions for counts of total num- bers of bacteria were removed from the bottle of soil and the remainder of the sample used for nitrification studies. Because of the great variation in the fertilty of different fields it was considered necessary to determine at what depths the nitrifying bacteria existed; therefore, instead of emptying the soil from the container and allowing it to dry, thus exposing it to some contamina- tion, one-half of the soil, approximately 50 grams, was removed with a sterile spatula and used for “original” determinations. Five cubic centimeters of 0.4 per cent ammonium sulphate was then added to the portion remaining in the botvle and the sample placed in the incu- bator at 28°C. With the original moisture of the soil this additional 5 cubic centimeters frequently made the water content of the soil somewhat above optimum, but owing to the rapid evaporation in an arid climate this rapidly decreased and was adjusted as nearly as possible in subsequent waterings. All samples were weighed at 3-day intervals, and as any appeared to fall below optimum the required quantity of sterile distilled water was added to restore them. The incubation period was two weeks, the temperature being maintained at 28°C. The chemical work presented no little difficulty. The analytical determinations may be considered in two phases: (1) The prepara- tion of the aqueous extract of the soil both before and after incuba- tion with ammonium sulphate and (2) the determination of nitrites and nitrates in original and incubated samples. In the preparation of the aqueous extract considerable difficulty was experienced. All of the soils used contaimed variable and fre- quently quite large proportions of very fine clay, which would not settle out and leave a clear supernatant liquid, even on prolonged standing. It was thought advisable to determine the chlorids and sulphates in the original samples; therefore the common salts con- taining these radicals could not be used to flocculate the clay, although this method was sometimes used in the examination of the samples after incubation where only nitrites and nitrates were deter- mined. Pressure-pump facilities were inadequate for the large num- ber of samples used, the more so as the fine clay particles clogged the porcelain filter and caused filtration to be extremely slow with the low pressure available.t| Heating the sample in the oven at different temperatures previous to adding the water seemed to have no effect, so the supernatant liquid was first drawn off turbid, evaporated to dryness, baked at 90° to 100° C., and then filtered. In all of the 1 Approximately 25 pounds to the square inch. py iy) Pp | 2st: METHODS EMPLOYED IN BACTERIOLOGICAL INVESTIGATIONS. ll baking experiments it was noticed that the nearer a set of samples was baked at 100° C. the better the subsequent filtering, probably indicating that the clay is siliceous. The Griess method is the standard for determining nitrites, but owing to the delay in getting chemicals at Fallon the potassium- iodid-starch method was used for a large part of the work. This method, while primarily a qualitative one, was found to be fairly reliable for quantitative determinations if a large quantity of reagent was used when the nitrites were high; as indicated by a rapid develop- ment of the blue-black color. The Grandval-Lajoux phenol-sulphonic acid method as modified by Syme‘! was used for estimating -nitrates ; before determining nitrates the nitrites were removed by urea in acid solution in accordance with Piccini’s method. Chlorids were frequently high in soil solutions in which nitrates were to be determined, and it was necessary to remove them when present ‘in concentrations greater than 50 or 70 parts per million. This was accomplished by the use of silver sulphate. Chlorids? were determined by the Mohr method, titrating the neutral solution with N/10 silver nitrate and using potassium chromate as-an indicator. Sulphates? were determined by the turbidity method described by the Bureau of Soils. DENITRIFICATION. Studies of denitrification were made by inoculating Dunham’s peptone solution containing 0.2 per cent potassium nitrate with soil and with a Frost scale measuring roughly the quantity of free nitrogen evolved. Either ordinary fermentation tubes or test tubes inverted in salt-mouth bottles were used. The latter method is preferred, as it permits the use of larger quantities of soil for inoculations. NITROGEN FIXATION. Leguminous plants were examined for the presence of nodules, and Azotobacter cultures were isolated from soil samples. 1 Syme, W. A. The Colorimetric Determination of Nitrates in Soil Solutions Con- taining Organic Matter. Thirty-first Annual Report of the North Carolina Agricul- tural Experiment Station, for the Year Ending June 30, 1908, pp. 64-65. 2 Both of these salts were determined by Mr. ©. A. Jensen, of the Office of Western Agricultural Extension of the Bureau of Plant Industry. 3 Schreiner, Oswald, and Failyer, George H. Colorimetric, Turbidity, and Titration Methods Used in Soil Investigations. Bulletin 31, Bureau of Soils, U. 8. Dept of Agriculture, 1906. 211 12 SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. NITRIFYING POWER OF SOILS AT DIFFERENT DEPTHS. In investigations in soil bacteriology in the eastern United States only the surface soil shows great variations. The soil of the arid sections is much deeper, however; that is, the subsoil is less ‘‘raw”’ than in regions of heavier rainfall, a fact that has come to be more or less familiar to everyone studying soil conditions over extensive areas. Figure 2 shows the nitrification of samples from plats 100 and 110. These plats, which are practically duplicates, are in a productive DEPTH AT WHICH SAMPLES WERE TAKEN. 0'706" 6’ 7012” 127018” iB7024" 247036" phates-Plat 1/0 : Oe erie Plato —- s S : 3 Q S . g R S S S 8 S S . a R S A FARTS PER M/LLION OF NITROGEN AS NITRATES. Fig. 2.—Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plats 100 and 110, Truckee-Carson Experiment Farm. Original nitrate present in samples from plat 100: Depth, 0 to 6 inches, 8 parts per million; 6 to 12 inches, 15; 12 to 18 inches, 9; 18 to 24 inches, 4.8; 24 to 36 inches, 6.56. From plat 110: Depth, 0 to 6 inches, 9 parts per million; 6 to 12 inches, 7.4; 12 to 18 inches, 5.2; 18 to 24 inches, 4.8; 24 to 36 inches, 3.12. alfalfa field which has been under cultivation for several years. The soil is loose and sandy throughout the 3-foot depth. The nitrate curves show that there is a gradual decrease in nitrifying power with depth. Figures 3 and 4 show the nitrification in samples from plats 120 and 5 130. These are in a fertile alfalfa field similar to the one mentioned 211 NITRIFYING POWER OF SOILS AT DIFFERENT DEPTHS. 13 : DEPTH AT WHICH SAMPLES WERE TA4AEN. 0'706" 67012” 127018" 187024" 247036" i SS {=e ; oa G — {ee eae = ao} oo & S Oh i a a S$ 700 Q ¥ a 600 1 ie ae a a ee AG) x S t N 500 S | J SSE ee Sa ee 2 4.00 ae re a S ~ ~ U iN) N 300 QV SOE ee ee & 20 200 ¥ : ‘ % q & i) : : X Fig. 3.—Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 120, Truckee-Carson Experiment Farm. Original nitrate present in samples: Depth, 0 to 6 inches, 15.36 parts per million; 6 to 12 inches, 8.64; 12 to 18 inches, 6.72; 18 to 24 inches, 3.84; 24 to 36 inches, 2.88. in the previous paragraph. The samples from plat 120 show nitrifica- tion varying rather irregularly with depth. Samples from plat 130 DEPTH AT WHICH SAMPLES WERE TAAEW. O76" = 6 70 12” 127018” 187024” 247036” Ne) S N - g : S S S CHLOAIDS ANO SULFATES. S S N S N N RQ S N FARTS FER MILLION OF Fic. 4.—Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 130, Truckee-Carson Experiment Farm. Original nitrate present in samples: Depth, 0 to 6 inches, 13.3 parts per million; 6 to 12 inches, 6.72; 12 to 18 inches, 9.6; 18 to 24 inches, 7.23; 24 to 36 inches, 14.4, 211 14 SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. practically failed to nitrify,' although the two plats appear to be very similar. Figure 5 shows the relative nitrifying power of good and poor soils collected from adjoining plats. Plat 160 has a loose sandy soil to a ae DEPTH AT WHICH SAMPLES WERE TAKEN. O706 67012” 127018” 187024" 247036" a 2 a Soc ng oO ro) ro) FARTS FER /4/LL/ONM OF CHLORIDS AND SULPHATES. FARTS FER MILLION OF NITROGEN AS NITRATES. Oo oO Fig. 5.—Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plats 160 and 170, Truckee-Carson Experiment Farm. Original nitrate present in samples from plat 160: Depth, 0 to 6 inches, 8.64 parts per million; 6 to 12 inches, 2.88;12 to 18 inches, 4.8; 18 to 24 inches, 6; 24 to 36 inches, 4.8. From plat 170: Depth, 0 to 6 inches, 4.32 parts per million; 6 to 12 inches, 6; 12 to 18 inches, 3.84; 18 to 24 inches, 3.6; 24 to 36 inches, 3. depth of 18 inches; below this it is very heavy, but below 26 and 30 inches it is again lighter in texture. At the time of sampling, this plat was supporting a fine growth of alfalfa. Plat 170 is in the north- east corner of the same field, and was very similar except that the 1 This field had been irrigated a short time’ before the samples were collected. 211 NITRIFYING POWER OF SOILS AT DIFFERENT DEPTHS. 15 surface was a little more compact and the alfalfa was practically a failure. The nitrification curves show the same general variations, but the one of the poor soil is consistently below that of the productive soil. QEPTH AT WHICH SAMPLES WERE TAKEN. 67012" 127018" 187024" 247036" PARTS PER MILLION OF CHLOAIDS AND SULPHATES. s : S S 19) = : ‘ S S n S N t N s N Fic. 6.—Diagram showing the nitrification of ammonium sulphate in samples of soil from different depths from plat 180 (poor soil) and plat 190 (good soil), Truckee-Carson Experiment Farm. Original nitrate present in samples from plat 180: Depth, 0 to 6 inches, 2 parts per million; 6 to 12 inches, 3.5; 12 to 18 inches, 8.25; 18 to 24 inches, 4.5; 24 to 36 inches, 25.75. From plat 190: Depth, 0 to 6 inches, 4.5 parts per million; 6 to 12 inches, 15.75; 12 to 18 inches, 11.25; 18 to 24 inches, 20.75; 24 to 36 inches, 21.75. Plats 180 and 190 are located upon poor and good spots. The texture of the samples is very similar, both being sandy, but the surface of plat 180, the unproductive soil, is hard and compact as if 211 16 SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. held together by some cementing material. As shown in figure 6, the nitrifying power of samples from plat 180 is almost nothing. In this figure the chlorid and sulphate curves are of interest, as those of plat 180, the poor soil, are far above those of plat 190, the good soil.’ DEPTH AT WHICH SAMPLES WERE TAIAEN. N O06" —- 6 F012" 2"r018” 18024” 247036" Ke SR 20 f - 200 ‘ SZ io Za Se S ; 55 loo NX SS et sete woLg - SX s (trates - Pig ; ear x N & & fe) === : QZ00 | --- — fe) c NJ ee ee ae fy ant oe ee ee ee a tame Bi