A112-1130-10,000-L180 TEXAS AGRICULTURAL QKPERIMENT STATION ' A. B. CONNE o TOR COLLEGE STATION, B ifixC i; FRI‘, TEXAS JANUARY, 1931 I “Alia BULLETIN NO. 421 M 1k ‘,,%:n~ ‘ Y! r1 . J " A Chemical and Microbiological Study of Lufkin Fine Sandy Loam in Relation to Productiveness AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS T. O. WALTON, President STATION STAFFT ADMINISTRATION: A. B. CONNER, M. S., Director R. E. KARPER, M. S., Vice-Director CLARIcE MIxsoN, B. A., Secretary M. P. HOLLEMAN, JR., Chief Clerk J. K. FRANcKLOw, Assistant Chief Clerk CHEsTER Hmcs, Errecutive Assistant C. B. NEBLETTE, Technical Assistant CHEMISTRY: . G. S. FRAPs, Ph. D., Chief; State Chemist S. E. ASBURY, M S., Chemist J. F. FUDGE, Ph. D., Chemist E. C. CARLYLE, B. S., Assistant Chemist WALDO H. WALKER, Assistant Chemist VELMA GRAHAM, Assistant Chemist T. L. OGIER, B. S., Assistant Chemist ATHAN J. STERGES, B. S., Assistant Chemist JEANNE M. FuEGAs, Assistant Chemist RAY TREIcHLER, M. S., Assistant Chemist RALPH L. ScHwARTz, B. S., Assistant Chemist C. M. POUNDERs, B. S., Assistant Chemist HORTICULTURE: S. H. YARNELL, Sc. D., Chief L. R HAWTHORN, M. S., Horticulturist RANGE ANIMAL HUSBANDRY: J. M. JONEs, A. M., Chief B. L. WARWICK, Ph. D ., Breeding Investigations STANLEY P. DAvIs, Wool Grader ENTOMOLOGY: F. L. THOMAS. Ph. D., Chief; State Entomologist H. J. REINHARD, B S., Entomologist R. K. FLETcHER, Ph. D., Entomologist W. L. OWEN, JR., M. S.. Entomologist J. N. RONEY, M. S., Entomologist J. C. GAINEs, JR., M. S., Entomologist S. E. . S., Entomologist F. F. BIBBY, B S., Entomologist CEcIL E. HEARD, B. S., Chief Inspector OTTO MAcKENsEN. B. S. Foulbrood Inspector W. B WHITNEY, Foulbrood Inspector AGRONOMY: E. B. REYNOLDS, Ph. D., Chief R. E. KARPER. M. S., Agronomist P. C. MANGELsDORF, Sc. D., Agronomist . T. KILLOUGH, M. S., Agronomist E. REA, B. S., Agronomist , Agronomist C. LANGLEY, B. S., Assistant in Soils PUBLICATIONS: A. D. JAcKsON, Chief VETERINARY SCIENCE: *M. FRANcIs. D. V. M., Chief H. ScHMIDT, D. V. M., Veterinarian F. P. MATHEws, D. V. M., M. S., Veterinarian W. T. HARDY, D. V. M., Veterinarian F. E. CARROLL, D. V.AM., Veterinarian PLANT PATHOLOGY AND PHYSIOLOGY: . J. TAIIEENHAUs, Ph. D., Chief . N. EzEKIEL, Ph. D., Plant Pathologist . J. BAcH, M. S., Plant Pathologist . F. DANA. M. S., Plant Pathologist M AND RANCH ECONOMICS: . P. GABBARD, M. S., Chief . E. PAULsON, Ph. D., Marketing . A. BONNEN, M. S., Farm Management W. R. NIsBET, B. S.. Ranch Management , Assistant RURAL HOME RESEARCH: JEssIE WHITAcRE, Ph. D., Chief MARY ANNA GRIMEs, M. S., Textiles ELIZABETH D. TERRILL, M. A., Nutrition SOIL SURVEY: **W. T. CARTER, B. S., Chief E. H. TEMPLIN, B. S , Soil Surveyor A. H. BEAN. B. S., Soil Surveyor R. M. MARSHALL, B. S., Soil Surveyor BOTANY: V. L. CORY, M. S.. Act. Chief SIMON E WOLFF, M. S., Botanist SWINE HUSBANDRY: FRED HALE. M. S., Chief DAIRY HUSBANDRY: O. C. COPELAND, M. S., Dairy Husbandman POULTRY HUSBANDRY: R. M. SHERWOOD. M. S., Chief AGRICULTURAL ENGINEERING: H. P. SMITH. M. S.. Chief MAIN STATION FARM: G. T. McNEss, Superintendent APICULTURE (San Antonio): H. B. PARKS. B. S., Chief FEED CONTROL SERVICE: F’. D. FULLER, M. S., Chief S. D. PEARcE, Secretary J. II. ROGERS, Feed Inspector K. L. KIRKLAND, B. S., Feed Inspector W. D. NORTHCUTT, JR., B. S., Feed Inspector SIDNEY D. REYNOLDs. JR., Feed Inspector P. A. MOORE, Feed Inspector E. J. WILSON, B. S., Feed Inspector wee“ FA mgr” SUBSTATIONS N0. l, Beeville. Bee County: R. A. HALL, B. S., Superintendent No. 2, Troup, Smith County: _ P. R. JOHNsoN, M. S., Superintendent No. 3, Angleton, Brazoria County: R. H. STANsEL, M. S., Superintendent No. 4, Beaumont. Jefferson County: R. H. WYcHE, B. S., Superintendent No. 5, Temple, Bell County: HENRY DuNLAvY. M. S., Superintendent B. F. DANA, M. S., Plant Pathologist H. E. REA, B S , Agronomist; Cotton Root Rot Investigations _ SIMON E. WOLFF, S., Botanist; Cotton Root Rot Investigations No. 6, Denton, Denton County; P. B. DUNKLE, B. S., Superintendent N0. 7. Spur, Dickens County: _ R. E. DIcKsON, B S., Superintendent , Agronomist No. 8, Lubbock, Lubbock County: D. L. JONEs. Superintendent FRANK GAINEs, Irrigationist and Forest Nurseryman N0. 9, Balmorhea, Reeves County: J. J. BAYLES, B. S., Superintendent No. 10, College Station,13razos County: R. M SHERWOOD, M. S., In charge L. J. McCALL, Farm Superintendent No. 11, Nacogdoches, Nacogdoches County: H. F. MoRRIs, M. S., Superintendent **No. 12, Chillicothe, Hardeman County: J. R. QUINBY, B. S., Superintendent A **J. C. STEPHENs, M. A., Assistant Agronomist No. l4, Sonora, Sutton-Edwards Counties: W. H. DAMERON, B. S., Superintendent , Veterinarian W. T. HARDY, D. V. M., Veterinarian **O. G. BABCOCK, B. S., Entomologist O. L. CARPENTER. Shepherd No. 15, Weslaco, Hidalgo County W. H. FRIEND, B. S., Superintendent SHERMAN W. CLARK. B. S., Entomologist W. J. BAcH. M. S., Plant Pathologist No. 16, Iowa Park, Wichita County: C. H. McDOwELL, B. S., Superintendent No. 17, — ———— , Superintendent N0. 18, ———-—— —————— —— , Superintendent No. 19, Winterhaven, Dimmit County: E. MORTENsEN, B. S., Superintendent N L. R. HAWTHORN, M. S., Horticulturist o. 20, i ‘ , Superintendent Teachers in the School oi Agriculture Carrying Cooperative Projects on the Station: W. ADRIANcE. Ph. D., Horticulture W. BILSING, Ph. D., Entomology P. LEE, Ph. D., Marketing and Finance ScOATEs, A. E., Agricultural Engineering . K. MAcKEY, M. S., Animal Husbandry *Dean School of Veterinary Medicine. J. S. MOGFORD. M. S., Agronomy F. R. BRIs0N, B. S., Horticulture W. R. HORLAcHER, Ph. D., Genetics J. H. KNOX, M. S., Animal Husbandry TAs of January 1, 1931. **In cooperation with U. S. Department of Agriculture. i '3 In a study 0f some of the factors 0f productiveness of Lufkin fine sandy loam soil at College Station, Texas, in 1925, 1926, and 1927, it was found that the nitrifying power 0f the soil was positively and significantly correlated with the yields of cotton and corn. The nitrifying capacity of the soil was a better index of the crop-producing power of the soil than the total nitrogen, the total phosphoric acid, or the active phos- phoric acid of the soil. The addition of nitrogenous materials, cottonseed meal and manure, and of phosphoric acid, as superphosphate and ground rock phosphate, stimulated the nitrifying power of the soil and increased the production of nitrates in field soil. Under conditions in the laboratory the addition of lime increased the power of the soil to produce nitrates, although this increased nitrifying power was not more significantly correlated with the yields of cotton and corn than was the nitrifying power of the soil without lime. Seasonal conditions did not influ- ence the nitrifying power of the soil under conditions in the laboratory, as indicated by analyses of samples taken at monthly intervals during the growing season. The continuous growing of cotton and of corn decreased the production of nitrates in field soil. The growing of corn on the same land every year also had a tendency to weaken the nitrifying power of the soil, a fact which apparently ex- plains why the yield of corn is reduced more by continuous cropping than is the yield of cotton. The accumulation of nitrates in the soil gradually increased as the season advanced, reaching a peak in July in the soil under cotton and in August in the soil under corn, and de- creased thereafter. The use of the statistical method appears to be a promising means of interpreting soil fertility data and increasing the reliability of conclusions drawn from such data. CONTENTS Pm Introduction . . . . . . . . . . . . .’ . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . Review of Literature . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . it 7 Method of Conducting the Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . Fertilizer Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ‘S; Time and Method of Taking Samples . . . . . . . . . . . . . . . . . . . . . ; . '1 Microbiological Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f Chemical Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microbiological Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 Effect of Crops on Accumulation of Nitrates . . . . . . . . . . . . . . . . 1p Effect of Season on Accumulation of Nitrates . . . . . . . . . . . . .. 1 V Nitrifying Power of Soil . . . . . . . . . . . . . . . . . . ., . . . . . . . . . . . .. i; Chemical Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l . . . . . . . . . . . ‘f Total Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ‘j Active Phosphoric Acid . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . . Total Phosphoric Acid . . . . . . . . . . . . . . . . . .* . . . . . . . . . . . . . . . Hydrogen Ion Concentration . . . . . . . Q . . . . . . . . . . . . . . . . . . , . . -. Statistical Analysis of the Data.‘ . . . . . . . . . . . . . . . . . . . . . . . . . 23? Correlation Data Obtained on Cotton . . . . . . . . . . . . . . . . . . . .. Correlation Data Obtained on Corn . . . . . . . . . . . . . . . . . . . . .. 2 i‘ Discussion of Results. . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . .; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..; Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. i? ' p , I a W ,1- q“ _V BULLETIN NO. 421 JANUARY, 1931 A CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN FINE SANDY LOAM IN RELATION TO PRODUCTIVENESS E. B. REYNOLDS Field experiments with fertilizers conducted by the Division of Agronomy, Texas Agricultural Experiment Station, on Lufkin fine sandy loam soil at College Station, Texas, from 1914 to 1921 showed that the soil does not respond readily to the fertilizer treatments used, as indicated by the yields of crops grown. This fact indicated that fac- tors other than plant nutrients were the cause of this lack of response. The fact also suggested that a study of the chemical and bacteriological activities of the soil might show the relation of these activities to the fertility of the soil, since investigations in various parts of the world have shown that certain microbiological activities in the soil as deter- mined by laboratory tests are indicative of the crop-producing power of the soil 0r the relative crop-producing power of two or more soils. Brown (7, 8) in Iowa showed that the nitrifying power and certain other bacteriological processes in the soil were correlated with the crop yields secured. Burgess'(9) reported that “Nitrification (soil culture method) is by far the most accurate biological soil test yet perfected for predicting probable fertility. In fact, it is probably the best single test of any description yet developed for ascertaining the comparative crop-producing power of arable soils.” Waksman (22) and a number of other workers have reported similar results. It has been found that different crops growing on the soil have a different effect on the bacterial activities of the soil. In view of the above facts it was thought desirable to make a study of the chemical and microbiological activities in the Lufkin fine sandy loam to determine if possible the relation of these activities to the crop-producing power of the soil under specific fertilizer treatments. Accordingly, an experiment was planned in 1921 to obtain information ~ 1 along this line. The work, unfortunately, was delayed until the sum- mer of 1925, when it was begun actively. Results were obtained dur- ing three crop seasons, 1925, 1926, and 1927’, and the data secured are reported in this Bulletin. REVIEW OF LITERATURE Microbiological processes in the soil have been studied by investi- gators for many years. Much work along this line has been done since 1877, when Schloesing and Muntz showed that nitrification is a biologi- cal process. The effects of various factors, such as temperature, moisture, air, organic matter, reaction of culture medium, various chemical sub- stances, fertilizers, plants, and difierent cropping systems on the vari- 6 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION ous microbiological ‘processes, have received considerable attentionl Nitrification is the chief microbiological process considered in the wor reported in this paper. It is not desired to review all of the literatur dealing with the study of nitrification, since much of it has no direc bearing on this Work. It is desirable, however, to consider the more important contributions pertaining to phases of the subject that ar involved in this investigation. The references given include those set " ting forth the effect of fertilizers, manure, cropping systems, and sea sonal conditions on nitrification. 3 Warington (23) at Rothamsted as early as 1878 showed that crops; and manurial treatment have an effect on the accumulation of nitrates} in soil. On (Broadbalk Field, devoted to continuous wheat, the soil, which received 14 tons of barnyard manure per acre annually for 38- years, contained about three times as much nitrate nitrogen as the manured soil. Similar results were obtained on the soil growing barley. Brown (5) in 1911 made a bacteriological study of field soils in Iowa“ The study was made on soil in eight different cropping systems includ- ing continuous corn; continuous clover; a two-year rotation of corn and oats; two-year rotations of corn and oats in which clover, cowpeas, and? rye were plowed under as green manure after oats; and a three-year rotation of corn, oats, and clover. The soil on the plats in the rota- tions had greater nitrifying and nitrogen-fixing powers than the soil on the plats devoted to continuous corn or clover. The use of green. manures did not increase the nitrifying power of the soil. The nitrify-i ing power of the soil was correlated with the yield of corn. Later ~ Brown ('7, 8) showed there was such a close relation between the baa-- terial activities studied and crop yields that a study of “bacterialf activities in the laboratory may indicate quite accurately the crop-pr0- ducing power of a soil or, at least, the relative crop-producing power of several soils.” f Brown (6) also studied the effect of manure on the soil in a four- year rotation of corn, corn, oats, and clover. Manure was applied atl the rates of 8, 12, 16, and 20 tons per acre. The applications of 12 .1 and 16 tons per acre brought about the greatest nitrifying power in J the soil and produced the largest yields of corn. He found that there v was a close relationship between the bacterial activities studied and the f crop-producing power of the soil. I- Lyon and Bizzell (15) made studies on the relation of certain higher f plants to the formation of nitrates in soil on which maize, timothy, mil- _1 let, and potatoes were grown. During the most active growing period of maize, nitrates were frequently higher in the soil under maize than f? in a cultivated soil that bore no crop. The soil under a mixture of‘ maize and millet contained larger quantities of nitrates than the soil "1 under the millet alone, although the crop yields were about the same in, both cases. _ Russell (21) at Rothamsted observed that land cropped to wheat and _f barley contained smaller amounts of nitrates than fallow soil. White (25) noted that crops influence the accumulation of nitrates CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 7 in the soil. Corn-stubble land contained 24.91 parts per million of nitrates; soil under clover sod, 13.14 parts per million; soil under clover and timothy, 9.23 parts per million; and soil under Winter wheat, 36.47 parts per million. ‘ Allen (3) found a close relationship between nitrification and crop production on plats devoted to continuous culture of crops, but there was no consistent relation between nitrification and crop production on the manured plats in a three-year rotation of corn, Wheat, and clover. Gainey and Gibbs ( 11) in Missouri determined the number of organ- isms, the ammonifying power, and the nitrifying power of a soil which received manure, chemicals, and no treatment under (a) six-year rota- tion, (b) continuous corn, (c) continuous wheat, and (d) continuous timothy. The untreated soils under continuous corn and Wheat had rather low nitrifying powers, Which, however, Were increased by com- mercial fertilizers. Albrecht (1) studied the effect of crops and cultivation on nitrate production. (He found that a reduction in the amount of nitrates occurred When the crop Was making the most rapid growth. With corn, nitrates accumulated until late in June, but decreased thereafter. No significant accumulation of nitrates ever occurred in oats and timothy sod, but a slight increase occurred after the crops were harvested. Albrecht (2) also determined the effect of long-continued treatments " on the bacterial activities of soil, especially under continuous oats and continuous wheat. Manure increased the accumulation of nitrates in if the soil and the addition of lime increased the nitrate content still ‘n, further. Prescott (20) in Egypt observed a relatively large accumulation of I nitrates in a typical Nile alluvial soil under cotton, but no such accu- — mulation occurred under Wheat or maize. Martin and Massey (17) also reported an accumulation of nitrates in soil under a growing crop of cotton. Yields of Wheat on unmanured soils were better Where the initial nitrate content was high than Where it was slow. Whiting and Schoonover (26) made a study of nitrate production in field soils in Illinois over a period of four years. The Work included iiseveral cropping systems and fertilizer treatments. The treatments i, consisted of crop residues, manure, green manure, limestone, and phos- ; phorus alone and in combination. The treatment of lime, manure, and g phosphorus brought about the greatest production of nitrates and the . largest yield of corn two of the three years in which yields were re- ported. The soil under the rotation of potatoes, corn, soybeans, and . alfalfa ('7 years) contained more nitrates than the soil under the other I rotations. Hall (12) in South Africa reported that land on which maize fol- ’) lowed cowpeas that had been cut for hay contained more nitrates than I. land on which maize followed maize. Baldwin, Nichter, and Lindsey (4) found that the rotation of crops on soils in Indiana increased the nitrifying power of the soil. Soil 8 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION cropped continuously to wheat and to corn exhibited a lower nitrifying power than soil in rotations of (a) corn, wheat, clover, and timothy; (b) corn, oats, wheat, clover, and timothy; (c) corn and Wheat; and (d) corn, oats, and wheat. ' Welton and Morris (24) in Ohio made a study of the yields of wheat; following potatoes and the relation of the nitrate content of the soil to‘ the yield of wheat. The work embraced one-, two-, three-, four-, andl five-year rotations in which wheat followed corn, soybeans, oats, clover, potatoes, and wheat. In general they found that the yield of wheat; was somewhat higher after-potatoes than after other crops. '- In 1922 and 1923 Murphy (18) in Oklahoma determined thenitrate‘; content and nitrifying power of manured and unmanured soil on which wheat had been grown continuously since 1893. Manure had been ap-I} plied at the average rate of 4 tons per acre for the last 26 years. The manured soil had a greater nitrifying power and contained about twice 1 as much nitrate nitrogen as the unmanured soil during the dormant period of the wheat. fi The relation of the nitrate content of soil to the yield of wheat in i seven different rotations of crops was studied by Karraker (14). The , largest yield of wheat and the highest average amount of nitrates were j obtained in the three-year rotation of tobacco, wheat, and clover during the five seasons. Karraker also made a study of the effect of crops on the production of nitrates in the soil during the season following the l’ growth of the crop. Tobacco, hemp, oats, soybeans, and corn were grown in small plats. The largest amount of nitrates was found in the soil "~ that grew soybeans and the smallest amount in the soil that grew hemp. A The amount of nitrates increased in the soil as the season advanced from April to August. ‘ METHOD OF CONDUCTING THE EXPERIMENT These studies were made on the soil under a four-year rotation of 5 cotton, cowpeas, corn, and oats, and under continuous cotton and con- j. tinous corn. The soil devoted to oats, however, was not included in the study because the oats occupied the land during the fall and winter I and it was desired to make the studies on soil under growing crops I during the summer months. The soil is classified as Lufkin fine sandy , loam. The surface is gray to ashy gray in color; the subsoil is a gray if‘ or mottled grayish and yellowish plastic clay. The topography of a typical Lufkin soil may be either fiat, gently undulating, or slightly rolling, and this together with the somewhat impervious nature of the i‘; subsoil, results in poor surface and internal drainage. The soil used if in these studies, however, has fairly good surface drainage, but the internal drainage is typical of the series. The Lufkin soils in general are 10W in organic matter and nitrogen. In the virgin state these soils, in Texas, are forested, the heavier types mainly with post oak, pi and the more sandy types with pine and mixed hardwood. ; These studies in soil fertility were made by taking samples of soil at CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 9 monthly intervals during the growing season from plats receiving vari- ous fertilizer treatments and analyzing them to determine the nitrate content, thetnitrifying power, total nitrogen, total phosphoric acid, and the active phosphoric acid. The data obtained from these analyses were analyzed by the statistical method to show the relationship of the sev- eral factors studied to the fertility of the soil as measured by the yield of crops. Fertilizer Treatments The following treatments were used in thesestudies: Plat No. Treatment per acre 1 200 lbs. superphosphate 100 lbs. cottonseed meal Crop residues removed No treatment—check 200 lbs. superphosphate 4 tons manure No treatment——check 200 lbs. superphosphate 11 tons manure 107 lbs. rock phosphate* 107 lbs. rock phosphate* 4 tons manure - 1O No treatment—check ‘L900 ~Q®UI+PUQIQ These treatments were applied to each crop every year. Time and Method of Taking Samples of Soil Samples of soil were collected in May, June, July, August, and Sep- tember, of 1925, 1926, and 1927. The samples were taken to a depth of seven inches at nine different places on each plat and a composite sample was obtained by thoroughly mixing these samples. Microbiological Studies The microbiological studies included the determination of the amounts of nitrates in the soil under the growing crops and of the nitrifying power of the soil. The nitrifying power of the soil, that is, nitrification in the soil under laboratory conditions, was determined according to the soil culture method of Brown (5), using ammonium sulphate. In 1927, the study included the nitrification of ammonium sulphate in the presence of the theoretical quantity of calcium carbonate required to neutralize the acids formed by the complete oxidation of the ammonium sulphate to nitric acid and sulphuric acid, as suggested by Waksman (22). In 1925 and 1926, the determinations of nitrates in the soil and of the nitrifying power of the soil were made on moist *The rock phosphate contained the same amount of phosphoric acid as the 200 pounds of superphosphate. 10 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION samples as obtained from the field, While in 1927 the determinations . were made on samples that previously had been air dried. In deter- y mining the nitrifying power of the soil enough tap water was added f to the moist or air-dry soil to bring the moisture content up to 60 per per cent of the water-holding capacity of the soil. The quantity of‘ A nitrates is reported as nitrate nitrogen in parts per million of water- free soil. The nitrifying power of the soil is stated as milligrams of = nitrate nitrogen in 100 grams of water-free soil. The nitrates in both T cases were determined by the method of the Association of Oflicial ~ Agricultural Chemists (19)-——eXcept in 1927, when Harper’s method Was used (13). Chemical Studies The chemical studies included determinations of (a) total nitrogen, (b) active phosphoric acid, (0,) total phosphoric acid, and (d) hydro- gen ion concentration of the soil. The active phosphoric acid was de- termined by F raps’ method (10) and the total phosphoric acid accord- ing to the method of the Association ‘of Official Agricultural Chem- ists (19). The hydrogen ion concentration of the samples collected in 1927 was determined by the colorimetric method. MICROBIOLOGICAL STUDIES The microbiological studies included the eifect of crops, season, and fertilizer treatments of the soil on the accumulation of nitrates and on the nitrifying capacity of the soil. These data were rather voluminous and it was deemed advisable to condense them into average tables for convenience of discussion. For instance, to ascertain the effect of crops on the nitrate content of the soil, the amount of nitrates under each crop at the several dates of sampling was averaged, and the averages thus obtained for the several crops were compared ‘directly. ln a like manner the seasonal effects on the accumulation of nitrates Were shown by averaging the amount of nitrates in the soil under all crops for each date of sampling. Effect of Crops 0n Accumulation of Nitrates in Soil The effect of cotton, corn, and cowpeas on the accumulation of nitrates in the soil during the growing seasons of 1925, 1926, and 1927 is shown in Tables 1, 2, and 3. The average nitrate content of the soil for any treatment is found by averaging the quantity of nitrates in the soil under each “crop receiving that treatment, at the five dates of sampling. For example, during the growing season of 1925 the average nitrate content of the soil on Plat 1 (200 pounds of superphos- phate and 100 pounds of cottonseed meal per acre) under continuous corn was only .71 parts per million, which is the arithmetic average of the nitrate content in parts per million of dry soil at the five dates of sampling, May 26, June 26, July 25, August 28, and September 30, 1925. CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 11 Season 0f 19251 Nitrates were present in rather small amounts in the soil under the growing crops (Table 1). This low accumulation of nitrates is undoubtedly due to the unusually dry season. The soil Was practically air dry at the first sampling (May 26) and at the third sampling (July 25) and the moisture content was lOW at the other samplings. Yet as an average of all the treatments, the soil on Which the rotated cotton was growing contained more than twice as much nitrates as the soil under either continuous cotton or continuous corn. The soil under crops grown in rotation contained relatively much larger quantities of nitrates than the soil under continuous crops, although the absolute amounts were small. In general the soil receiving manure contained relatively larger amounts of nitrates than the other treat- ments. The soil on which all crop residues have been removed since 1911 contained the smallest amount of nitrates. While there was some observable effect of crops on the accumulation of nitrates in the soil, it may be stated that the unprecedented dry season of 1925 prevented a typical expression of the effect that crops may have on the accumula- tion of nitrates in the soil, as will be indicated by comparing the data obtained in 1925 with the data obtained in 1926. 36118011 0f 19261 The soil under crops grown in rotation (cotton, corn, and cowpeas) contained significantly larger amounts of nitrates than the soil under continuous cotton or continuous corn (Table 2). The soil on which rotated corn was growing contained, as an average for the season, 18.18 parts per million of nitrates in dry soil, as com- pared with 8.58 parts per million for the soil under continuous corn. The results are in agreement with those of Brown (5) in Iowa. The soil under rotated corn apparently showed less variation in nitrate con- tent among the different treatments than the soil bearing the other crops. The largest amount of nitrates (17.45 parts per million) oc- curred on the plats receiving rock phosphate and manure under rotated corn. This treatment also produced the largest amount of nitrates (17.43' parts per million) in the soil under cowpeas. The treatment of manure and superphosphate brought about the greatest production of nitrates in the soil under rotated and continuous cotton. Season 0f 19271 There Were no great differences in the quantity of nitrates found in the soil under the different crops during the season of 1927. The soil under continuous corn, however, in the case of every treatment, contained smaller amounts of nitrates than the soil under other crops (Table 34')‘ The soil under rotated cotton and under rotated corn contained on the average equal amounts of nitrates during the season. l Considering the results for the three years of the experiment, it may be stated that the crops and cropping systems used affected the accu- mulation of nitrates in the soil. The soil under rotated cotton con- tained the largest amount of nitrates during the crop seasons of 1925 and 1927, but the soil under rotated corn contained the largest average 12 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION . . . . . . . . . . .. wofifl QVNA m5: 5.: m9»; omdfi . . . . . . . _ . . . . . _ . . . . . . . . . . . ..v_uwnul¢cozfiwvb. oZ 2 MR2 mew: 3 . S B. Z 5i: moflfi . . . . . . . . . . ..o.:EwE m5: v fifiimogg x03 .2: >2 m hv I 3Q 8a 3.2 $92 91: . . . . . . . . . . . . . . . . . . . . .... mswpmwazg x2: f: >2 w $1.2 fim m; >93 $2 $12 092 . . . . . . . . _ . 6552: g3 q Bfigmonnhwgfi i: 8N N. and mmtm m5: wmdfi wqmfi mod . . . . . . . . . . . . . . . . . . ... . . . . Iixowfloiacwefiwwhfi oZ w ZYNH omfmfi final wfliofi mmql and . . . . . . . . . . . . . . . . . . . . ......o.5awEw=o~¢ m . . . . Q mfliw wog. v92 mwh o9: wofl . . . . . ......................xuwaul~cwi~mvhi oZ m ES mfiw flaw mob 3.2 mwh . . . . . . . . . ................igoflcohwwsimfiQED N N“; NNQ Ea 2 . 2 2 .2 ma. . . .22: wmxVSSSQ .2: o2 asfiiwoirmé=w .2: 8N H vE -Q -m -E.Q -m ¢E -Q ¢m -E.g IL 64a 0m -E -g ¢m wmm$>< wwvaBoo .538 cofioo Eco Eco ohm». :5 acvcfimokH dZ wwfifiofl Bfifiofl wsoscficou wwflfiofl wsoncicoU “EA cmmfi dfimfizoi nrwnfifimvm 3 >32 .303 Qcohvwmw QQUQU mom 5w we c051: 5Q 2.6m E cvmobm: 33$: “o win-GEN @m§6><1\.m QEFH . . . . ‘ . . . . . .. wm; mm; mnmo C; 3L6 .................................@mm~o>< ma; m»; Sim mo. H Ed .2; . . . . . . . . . . . . . . . E . . . . . . . . . . iséolzsnsxmzp oZ 2 m». fl min 3w Q5 £5 2 . H ........3scmE 23 w afifiiiq “.62 an: R: m . . . . . . . . . . . . . . . . . . .......UHNSQWQSQV~OQH .WQ.— @ $1 ~ 8% fi 8. m 5A in; was . . . . . . . E . . dbEmfi mac“ ¢ acwfiwcpmhomfi“ .2: o8 N. and wwd ow; omio mad wvd . . . . . . . . . . . . . . . ........xo2~o.|~=wE~wo.5oZ w S“; mm; ca; wad 2N mad . . . . v . . . . . . . . . . . . . . ...........Iéiscwfimcoav m . . . . . . . . . . . ........-.....QHWZQMQ§QMUQ:W ¢ wad mwd $4 mfiio mm; mmd . . . . . . . . . . . . ....xuvaoil...conbwv.fioZ m whd Mfiio 2A Rio mad 5X0 . . . . . . . . . . . . Iuwizcuhwvsummuhnohu N S; £4 3. H m3. mo; is . .186 wwvmqoxao .2: o2 .B_E%¢_E:.Q=m .2: 8N fi E-Q.m E-Q-m -E-Q-m .E.Q-m .E.Q-m E-Q-m . wmm~w>< mmvmBou c038 cofiou Eco Eco v5.6 Sm Hcwsbmogk .02 wofiflofl wfifiom msosaficou wwfifiom wsosnficoU XE mug 633x05 Qonifimow 3 >22 £950 acawwav 5cm: mow Eu .3 c0215 5n 3:3 E cumoutc QESE Mo QCEOEN vmmhzfiwll; nznwmfi CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 13 amount for the three years, which was due mainly to the large amounts in the soil in 1926 after the corn had ceased taking up nitrates. The soil under continuous cotton and under continuous corn contained smaller amounts of nitrates than the soil undera rotation, indicating that the continuous growing of one crop on the soil has a depressing effect on the accumulation of nitrates. Correlation Between Amount of Nitrates and Yield of Cotton: A sta- tistical analysis of the data obtained in the experiment was made, the results of which are discussed later, but a discussion of the correlation existing between the quantity of nitrates in the soil and the yield of cotton and corn is pertinent here. In 1926 the correlation coefficient between the average amount of nitrates during the season and the yield of continuous cotton was .552 i155 ; while for rotated cotton the cor- relation coefficient was .491 i.162, both of which are significant (Table 13). In 1927 the correlation coeificient between the amount of nitrates and yield of continuous cotton was .700 i.109 and of rotated cotton .389 i.181, the former being significant. These results indicate that the yield of cotton has a tendency to be closely associated with the amount of nitrates in the soil. Correlation Between Amount of Nitrates and Yield of Corn: There appeared to be no correlation between the yield of continuous corn and the amount of nitrates in the soil during the crop seasons of 1926 and 1927, as indicated in Table 14. On the other hand, there was a sig- nificant negative correlation between the yield of rotated corn and the amount of nitrates in the soil, the coefficient of correlation being —.'781 i.083 in 1927. Since there was significant positive correlation between the quantity of nitrates in the soil and the yield of both rotated and continuous cot- ton during the two years and since there was negative correlation be- tween the amount of nitrates and the yield of rotated corn and little or no correlation in the case of continuous corn, it is concluded that the yield of cotton was more closely correlated with the quantity of nitrates in the soil than was the yield of corn. This is probably due to the fact that cotton puts on fruit over a rather long period and used nitrates during most of the period, while corn is a determinate type of plant, setting its fruit during a short period of time, and perhaps did not take up nitrates from the soil after the sampling in July. The results indicate that under the particular conditions cotton was a better “soil indicator” than corn. Effect of Season on Accumulation of Nitrates The amount of nitrates in the soil at each date of sampling in 1925, 1926, and 1927 is given in Tables 4, 5, and 6. The quantity of nitrates for each date is the average amount found in the soil under the five crops. For example, the soil on the plat receiving 200 pounds of superphosphate and 100 pounds of cottonseed meal per acre contained 14 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION - . . - . - - - - - .. ...-.-.¢-..-............-...-..®m$v~@>< wmw wad mwd mmw ww. w mofi . . . . ... . . . . . . . . . . . . . . . . .... iovnoiwcvfiwwwww o2 ow m». w on. w ww. w ww .N wmw wmw . . . . . . . . . . IoEEmE 28 w owwnawosn x2: .9: h: a . . . . » . . . - - - . - - . - . - - . . . - - w mm. w mm. w is H: oww E4 . . . . . . . . . . dEcwE meow w mfifiwwozévng i: 8N w. and mmd N90 wwd wwmo nmw . . . . . . . . . . . . . . . . . . . . . . ..vwooso|w:oEw§Zw oZ w mww N50 wwd mow mww 51m . . . . . . . . . . . . . . . . . . . . . . . . .........QbEmEw:oww m x@-o . . . . - . - ¢ . - . . - . .... - - . -. . € wad mod ww.o mww wad mmw . . . . . . lxownolucowcwmvpwoZ m wwd mmio ow.o wwd wcw www . . . . . . . . . . . . . . . . .......w.v>oEv.;@:EmE QSU N wow Q; Ms .0 S. w 2 . w 5w . 113E waQESHQQ .2: oow Qzfinwcpghugfi .2: 8N w 0E .n -m E-Q -m uE .Q -m 1E -Q .m ‘E -Q -m E-Q -m 67w . owm$>< om JQQW mm isms/w mm 33. mm 25w. on >32 30m 5Q wavifivbfiw. wfinw mmmw E mowmw. Eohuwmw an mow aw Lo cozmi 8n 2:3 E cemobmc owmbw: we wcsoE<|w ownflw. ... -.-~. --.---.--» . - . - ' - - - - -..--»-Q%QPQ>< wwmw mow wmw. Chm mwww wmw . . . . . . . . . . . . . . .....v_uwno|wcoEwmokw oZ ow 0N8 fig Ea wmm wwfi mmw ... . . . . .. . . .3555 .88 w 3228.2 v62 an: t: a omh an...“ hwé wad omb mwh . . . . . . . . . . . . . . . . . . . . . . . Qowwwwawowwa x03 .2: how w $5 5m S; mwb wwd mwmm . . . . . . . . . . 6552b mcow w vfifiwamoaapwmsw .2: SN h www mmiw hwb cub wwmw no...“ . . . . . . . . . . . . . . . . ..xowwwo|lwcwfiwmwb oZ w wmh bwd www. mwtm nob wwfim . . . . . . . ........o.5cwEw:oww m Nfi-w .fi . . - - - - - - - - - - - - - v - . . ~ - - . . q mww 59m hw b ww.w ww.w 5d . . . . . . . . . . . . . .. . . . . . . . . . . Ulxousolgcwegmolfl‘ oZ m mwh wTm wmw mwh wmiw wwfl . . . . . . . . . . . . . . . . . ......wvw>oEvww@swzwvh no.5 N mm .w wow 3a Q .w mw .w mwa . .435 83.6300 .2: oow dwmsamonabasw a»: 8m w -E-Q-m E-Q-m E-Q-m E-Q-m -E.Q-m ~E.Q-m omw$>< mmwwivoo cotbo cowwou Eoo Eco 05m :5 wcownwmoflw. 67w wvowfioww wxfimwoww wsoswicoU wvwwwomw wsoscSaoU wfinw hmmw 6231.5 Qvnimzqum ow >34 .305 Eowowmw. .605. mom F5 we c258 won mfimn E cwmopflc owwbm: mo wcsofim omm$><|nm 03w? CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 15 4.62 parts per million of nitrates on May 1'7, 1926, which was the average amount of nitrates in the soil receiving the treatment on con- tinuous cotton, rotated cotton, continuous corn, rotated corn, and rotated cowpeas on that date. It should be pointed out that averaging the figures in this manner may mask the eifects of the individual crops. Since the same crops are present in each case, the average does not introduce a variable although it may mask or obscure the influence of the individual crops, as mentioned above. Season 0f 19251 During the growing season of 1925 the amount of nitrates was unusually small at every date of sampling (Table 4;). In a general way the accumulation of nitrates in the soil did not vary much during the season. The samples collected on May 26 had a greater concentration of nitrates than the samples taken on the other dates. The lack of moisture, however, was the controlling factor in the production and accumulation of nitrates at all times during the season. Even though nitrates were present in such small amounts, the soil on the plats which received manure contained relatively larger amounts of nitrates than the soil which received other treatments. The plats on which the crop residues Were removed had the smallest amount of nitrates. 3688011 0f 19261 In 1926 conditions were much more favorable for the accumulation of nitrates in the soil than they were in 1925. The average quantity of nitrates in the soil increased from 5.51 parts per million in May to 16.411 parts per million in August and decreased thereafter (Table 5). A nitrate content of 16.41 parts per million ap- parently is a high concentration of nitrates in Lufkin fine sandy loam. The soil treated with manure had larger quantities of nitrates at each date of sampling, as a rule, than the soil receiving other treatments. The soil on which the crop residues were removed contained, on the average, less nitrate nitrogen than the soil receiving other treatments. 3888011 0f 19271 The average quantity of nitrates in the soil as de- termined from the average of all crops and treatments, decreased from May to July and August and increased thereafter (Table 6). The soil which received manure and rock phosphate contained the largest, and the soil with the crop residues removed the smallest amount of nitrates during the season. The soil from which the residues were removed contained the smallest average amount of nitrates during each of the three years. The conditions in 1927 were not as favorable for the pro- duction and accumulation of nitrates in the soil as were the conditions in 1926, as may be seen by comparing the results in Tables 5 and 6. Nitrifying Power of Soil Soils from the difierent plats were studied from the standpoint of their ability to nitrify ammonium sulphate according to the method N 0 Y; T A T S T N E M I R E P X E L A R U T L U 0 I R G A S A X E T 1, 2 4 0 N N I T E L L U B 16 wmmfl 5 n33. puvhubzv i». mow Eu Ho 50:25 SQ 3:3 5 GQMOHZQ 3955 mo ..E:o5<.|.m oEmP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ZOWGMO>< m . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ll Ea $6 . . . . . . . .....v5cm5 53 w dfiwmwmmnngflmdmwfigw%m._w NwoH/flfi m~ wmfm. . . . . . . . . . . . ....... . . . . . ..... . vmmm Rm“. 3m . . . . . . . . . . .2585 53 w .%ga%fl~~mwwwwv~-._m_kmfimmm w. fiw.ww . . . . . . . . . . . . . . . . . . . . . . . . . . .v~OOSOI|HCQEHGQMH Oz Aw . . . . . . . . . . . . . . . . . . . . . . . ........-.Q.~5§NEw§Q . . . . . . . . . . . . . . . . . . . . . . . . . .®wN£QwOSQ.~0Q5m fi . . . . . . . . . . . . . . . . ..MOOSOI#GQEMNQ.S.OZ M. . . . . . . . . . . ..~.@Q>OEQHwQ5@@m..n.vk QOHU N .5 d Q 5 d Q 5 d Q .5 d Q .5 dLQ dwanmm ~ w 0503c“. 2: o2 wfiwaamonahwnsm, m5 oom w w , . a o 52/4 mm Bow wfi Gsmflé. wfi 33. wfi .53. wfi >32 v55 :5 QGQEQQMKH. Hmw/HHM BN2 5 35% Qcohubmmw 5 mom >5 mo 55x5 5Q mfimn 5 cuwobw: @555 we 5:o5<|.w “imam. ~ ¢ » - - - - ~ . ¢ .. . . . . - . . ~ - . . - - - - - - . ¢ -- - - - - | vnnoonommho>< . . . . . . . . . . . . . ... . . . . . . ........ Nmflfi 5.5 . . . . . . . c.5555 53 w dwwmwmwvywflvfiflmmwawmnwmxfwfifi w: . . . . . . . . . . . . . N52 Qxfi fiwm a $2.2 . . . . . . . . . . .3585 53 w mwwwmwwwmpwmmm w QN.@ . . . . . . ... . . . . . ....... . . . . ..V~OUSO||I#QQE..—GQ.S. Oz mw MmQH 6N ww Nw m: ON PM QNQ Nwm . . . . . . . . . . . . . . . . . . . . .............0.~S=wEwQO . . . . . . . . . . . . . . .UQNZQWO§Q.~QQUW .MQQ 5 . . . . . . . . . . . . . . . . . ..v~UQSOI|HGQEHNQ.~H Oz m 2w. wmd 3.3 Wm? 1.5. . . . . . . . . . . 1.63225»! $533.- QQU N .5 . Q .5 d Q .5 d pm .5 d d .5 d N um _ 5 wvwmcofiou ma: 2: BEEWOQQEQQE d5 8N w w . 5.2 o m~w>< S .33 S $53.. 2 fish. m: 05;. “A >32 96w :5 5o5~w3P 22m CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 17 suggested by Brown (5). These studies were made during 1926 and 1927. Season 0f 19261 The soil from the plats under continuous cotton ex- hibited a much greater nitrifying power at each date of sampling than the soil from the plats under the other crops in 1926 (Table '7). Con- sidering all the treatments, this soil was able to nitrify, on the aver- age, 26.6 per cent of the nitrogen added in ammonium sulphate in four weeks, while the soil from the plats growing continuous corn, rotated cotton, rotated cowpeas, and rotated corn, converted into nitrate 11.9 per cent, 16.8 per cent, 1'7.9 per cent, and 20.7 per cent, respec- tively, of the nitrogen added. If the effects of treatments are considered, equally striking results are noted. The soil treated with manure and superphosphate gave the highest nitrifying power for the season of 1926 when the results ob- tained from the soils under all the crops are averaged (Table '7). In general, the soils on Plats 5, '7, and 9, which received nitrogen, either in the form of cottonseed meal or manure, showed a more vigorous nitrifying power than the other soils. Perhaps the most striking fea- ture of the data in Table '7 is that the soil from Plat 10, which received no treatment, showed the weakest nitrifying power with every crop. This soil, however, had a much greater accumulation of nitrates than the soils from Plats 3 and 6, which also received no treatment (Table 2). The cause of this discrepancy is not apparent from the data, al- though the greater hydrogen ion concentration might have been respon- sible (Table 12). The application of phosphoric acid, either in the form of superphosphate or rock phosphate, increased the nitrifying power to some extent but not as much as the cottonseed meal or manure. Seasflll 0f 19271 Two series of tests were made in 1927. In one series p ammonium sulphate was used alone and in the other suflicient calcium carbonate was added to keep the reaction basic. The addition of lime with ammonium sulphate greatly increased the nitrifying power of the soil as compared with ammonium sulphate alone, the former producing about six and one-half times as much nitrate as the latter (Table 8). This is an interesting fact, since it was not expected that the increase would be so large. The lime appeared to reduce the variation in the nitrifying power of the soil receiving various fertilizer treatments. The nitrogenous materials, cottonseed meal and manure, increased the nitrifying capacity of the soil. Superphosphate and rock phosphate increased slightly the power of the soil to produce nitrates, but not to the same extent as the manure and cottonseed meal. The soil under continuous corn exhibited a slightly greater nitrifying capacity than the soil under the other crops during the season of 1927. Considering the results for the two years, it may be said that the soil treatments affected the nitrifying power to a considerable extent. In general, the soil which received nitrogen, either in the form of cot- tonseed meal or manure, had a greater nitrifying power and contained wwwN E. m mm mN mm N 23w 3 m 2am 2: m :3 92+ 2w wm. www . . . . ........vmw$>< N 2.2.8 hNN hN Z .3 2 @062 NwN 3.2 8 2 3 2N 2: ms wN maN . IYITJZQ O NméN mmw ww wN mmN MZSN mNw 98mm wmw 2m mN wmw B wm $2 . . jib W... wwdN Em Nm mN NNm hwéN mmw mmAN m.» N 2o mN omw g om 5.», . .%..,...w . a H . . . . . . . . . . . . . . . . . . . . . . . . A fim E m Wm i M“ i .2 2 m mm ......... W M RWSN mm w we mN mN w 5.5 NN w mmbN mm w ww wN 5b 5 2m :6 . . . . . . . . . . . . . . . . . 1m. 8.2m No w ww mN ow N MKAMN w... m. mNMNN S m n2 wN 3.2 2o NN t; . . . . . . . . . . . . . . . . . . . . . 1w m fi M2 2x2 22m 2x fi wnUMMmummmfluwwnMwmwuwumm M wN.wN 8 m mmbN o2 m MZSN om m nN mN 0o w 3 NN 26.2 wmdN WK.” . . . . . . . . . . . . . . . . .. .. m E2 m2 E2 m2 .22 E2 m2 E2 32 .22 .22 .32 %. mOUmU 0:24 mOUwU @252 mOUmU use?‘ mOUmU 25?. mOUmU 2224 mOUmU v5.2 Q @3223 352325 vq-msfirsm oamafisw QEEQGZ ogmnaii EEcoEE< EEcoEE< 52.225554 EE:oEE< EEcoEE< EE=oEE< dz 22m L A omwho>< Q3233 . c0300 cofioo Eco Eco W“ wvfifiofl . 353cm wsoscflcoU wvfifiofl wsosEEou T . fi hmmfi dZwBBE 52:68am o2 - C 2x2 do» in 2o wcbfim 002 E cwmobE 395E .3 wcbfimsmi mm @3822? com 2o .6302 wEfiific wwm2o>< X ow 5N Nw hwN :2 2.2 v2 fie 2w mmN mw mwN . . . . . . . . . . . . . . . . . . . . . I02 E wwm ww h a m2 5 m m wN aw n NQw .52 mdN £2 > 3 2o m . . . . . . . . . . . . . . . . . T $2 mm 2x m“ w; 2.2m M? .22 2x $2 22222222222222.2222“. 2M2 Mfi. m2 2x x2 fi M22 m? x2 ma 2x 2.222222222222222“... O. 2 >2 E m 2. >2 0mm 0.2 oww NNN 3.2 m? 3.2 Na Em . . . . . . . . . . . .. N N 3 wN w w m2 No w o 3 5 m wAN w b v2 Kw m a owN . . . . . . . . . . . . . . . . . . . . . I o3 Nww 2 wH mNm >2 NNm f: w m 2.2 2..., m w mwN . . . . . . . . . . . . . . . . .. N moN wow moN m2 2 >2 Sm N. N was . N.wN NNB h m2 N2.w . . . . . . . . . H “m. .32 Q. E2 N. .32 Q .22 N. 22 $ .32 E Q omm~o>< $22300 . cofioo nofioo Eco Eco dZ 2x7? U uvfificfl @3233» wsoscficoU vwfifiofl waoaEfi-onu B w 2222230 SQ 002 ma mfiwwmszE om :0 wwwan mcwmwn 322E cawvonmwwwo cwlfifi: .20 o @3235 3S 6am: v33 32E Em EsEoEEw E av obi o 9E2 .: i: iii. . m2 dZwEuE. H Qonfifiaum 3 was». .396 “Ewhuwmw SEE mmom E v2.5.5? @2231; E5mGOEEm~ E comobr: .20 om~fi$o2ww2 can QQDOEN omw2o><.|.> 033w CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 19' more nitrates than the soil receiving other treatments. The soil treated with 4 tons of manure and 200 pounds of superphosphate showed a more vigorous nitrifying power than the soil which received other treatments. The soil under rotated corn had a greater nitrifying power than the soil under continuous corn. On the other hand, in 1926 the soil under continuous cotton had a much greater capacity to produce nitrates than the soil under the other crops. These facts seem to indicate that cot- ton may be grown continuously on this particular soil with less reduc- tion in yield than corn. This apparently is confirmed by published data on the yields of crops on the plats used in these studies over a period of 14 years, in which it is shown that the yield of continuous corn declined more than the yield of continuous cotton (Texas Agricul- tural Experiment Station Bulletin 390, 1928). Correlation of Nitrifying Power with Yield of Crops: The preceding discussion considered the nitrifying power of the soil in relation to the various treatments. It is desirable at this point to show briefly the relationship between the nitrifying capacity of the soil and the yield of cotton and corn. Accordingly, coefficients of correlation were computed to show this relationship. The correlation coefficient between the yield of continuous cotton and the nitrifying power of the soil was .746 i.095 -in 1926 and .789 i.081 in 1927, both of which are significant (Table 13). The correlation between the yield of rotated cotton and the nitri- fying capacity of the soil was significant in both years, being .833 i.O65 in 1926 and .829 i.067 in 1927. Significant positive correlation was found between the yield of con- tinuous corn and the average nitrifying power of the soil, the coeflicient being .742 i.096 in 1926 and .658 i.121 in 1927 (Table 14). For corn grown in rotation the coefiicient of correlation was .576 i.143 in 1926 and .192 i206 in 1927. The correlations obtained with corn indicate that the yield of corn is more closely correlated with the nitriiying capacity of the soil than with the amount of nitrates in the soil under the growing crop. CHEMICAL STUDIES The chemical studies included analyses for total nitrogen, active phosphoric acid, total phosphoric acid, and hydrogen ion concentration.‘ Total Nitrogen It will be observed that the soil which received nitrogen, either in the form of cottonseed meal or farm manure, contained, as a rule, slightly more nitrogen than the soil which received no nitrogenous manures (Table 9). For instance, Plat 1, which received annually 200 lThe author is indebted to Dr. G. S. Fraps, Chief of the Division of Chemistry, Texas Agricultural Experiment Station, for determinations of total nitrogen in 1926, of active phosphoric acid in 1925 and 1926, and of total phosphoric acid in 1926. 20 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION :5 m. 8. Q om B: wm wm B . . . . . . . . . . . . . . . . . . . . . ... Qovnolfihocfiwofi o7: o: S: o: 2: w:: mo: on: ::: 3: t: . . . mwmamwmn. M13 w 82325.: x2: i: S: o om: mo: ow: mo: w: § wo: :w: mm: :5 . Modifies: :00: .2: B: w S: S: m: mw s2 $2 S; mm m: m2 @5551 53 w o:5::mo::$::w é: 8m h mm S. ow om :m ow 3 ow mm i“ . . . . . . . . . . . . . . J:o2:o|5o5:w@.5 o7: o mo g :6 3w wo mo on 3. i. w» . . . . . . . . . . . . . . . . . . . . . 65555 mac: v m w: w: mo: .2: 3: om: on: :o m: mm: . . . . . . . . . . . . . .35::mo::5::m .2: oom w 3. mm om om 2. ow :w mm 5 ww . . . . . . . . . . . . . . . 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B... . . . . . . . . . . . . . .o55...5 5o: w n N8 $5. 3o £5. :5. 3s $5 $5 So mmo. . . . . . . . . . . . . . .3m::mo::._o::w .2: oom w 3o. N3. :8. 8a. owo. Nwo. owo. $9 NS. m3. . . . . . . . . . . . . . . . .v:oo:o|5o5:wwb o7: m $5 £5. $5. 25. wwo. :3. N8. omo. m3. £5. . . . . . . . . . . . . . . .:6>o5o: mvififi :50 N m8. omo. ca. omo. NE. m3. 8a. moo. 95. m8. . . . . . . . . . . . ... . . . . $5 wnxafizo» .2: oo: Q52: wo:::$::m .2: oom : .52 £2 S2 omo: hm»; _ $2 R2 32 “No: $2 95w 50:. 5v5fiwwfifi .07: 30:33 50500 nofioo Eco 55o .37: oofifiow: ovfifiow: wsosfifihoU onfiwoom: 2555500 “ha: S32 was 6mm: $32 5 m:o.:o .655 ovfixioo :3 :0 mo::5mm n: ummohfi: :0 @m8_=8$:|.@ Bash. CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 21 pounds of superphosphate and 100 pounds of cottonseed meal per acre, contained more nitrogen than either Plat 2, which had the crop residues removed yearly since 1913, or Plat 3, which received no treatment of any kind. Plats 5, '7, and 9, which received 4 tons of manure With or without phosphoric acid, had more nitrogen than the nearest untreated check plats. These data also show that the percentage of nitrogen increased progressively from Plat 3 to Plat 10, when all the plats on the five blocks are considered. The percentage of total nitrogen was positively correlated with the amount of nitrates in the soil under the growing crops and with the nitrifying power of the soil, as shown in Tables 13 and 14. The cor- relation, however, was not significant in all cases. Active Phosphoric Acid In most cases the addition of phosphoric acid in the form of super- phosphate or ground rock phosphate increased the amount of active phosphoric acid in the soil (Table 10). The soil receiving rock phos- phate contained as much active phosphoric acid as the soil receiving equal amounts of phosphoric acid in the form of superphosphate. These two forms of phosphoric acid have been equally effective in increasing the yield of cotton and corn (Texas Agricultural Experiment Station Bulletin 390). The kind of crop or the season appeared to have no consistent effect on the amount of active phosphoric acid. While the amount of active phosphoric acid in the soil was closely associated with the application of phosphatic fertilizers, there was no significant correlation between the amount of active phosphoric acid and the yield of cotton (Table 15') or the yield of corn (Table 14). The yield of cotton in 1926, however, was correlated to some extent with the active phosphoric acid, the coefficient of correlation being .447 i171 and .426 i175 for continuous cotton and cotton grown in rotation, respectively. Significant positive correlation was found between the active phos- phoric acid and the average nitrifying power of the soil under continu- ous cotton, under continuous corn, and under rotated corn in 1926. The coefficient of correlation was .557 1.147 for continuous cotton (Table 13), .584 1.141 for continuous corn, and .603 1.136 for rotated corn (Table 14). Total Phosphoric Acid The Lufkin fine sandy loam soil used in the experiment is low in phosphoric acid, as shown in Table 11. The addition of phosphatic fertilizers, however, has increased to some extent the percentage of phosphoric acid in the soil. For example, the soil on Plats 1, 4, '7, 8, and 9, which have received phosphoric acid in the form of superphos- phate or ground rock phosphate, contained more phosphoric acid, as a rule, than the soil on Plats 3, 6, an.d 10, which have received no fer- tilizer treatment of any kind since 1914. The total phosphoric acid in the soil was significantly correlated with N O n A T S T N E M I R E P x E L A R U T L U C I R G A S A x E T 1, 2 4 O. N m T E L L U B 22 28 28 o8. o8 28. o8 H8 o8 So o8 . . . . . . . . . . . . ..M:3:QI:=.EGQ: oz 2 S8 o8. o8. o8 28. 8o :8 S8 So o8 5.5.56 2:: v M22225: :2: .2: >2 o :8 S8. o8. o8 o8 So So 8o S8. 8o . . . . . . . . . . . . . ....€:omo:o :2: .2: >2 w H8 $8. o8. 8o 18 18 o8. 8o o8. moo ahéwfiéoo: @2..:o2.:.:2:a .2: ooS h :8 S8 28. 2o to o8 28 :8 So So . . . . . . . . . . . . . . ..:QQ:..T..:=QEEQ: oz o :8. o8 o8. o8 S8 8o o8. So So o8 . . . . . . . . . . . . . . . . . . . . . .2255 2.8 < o o8. . . . . . . . . 28. o8 o8 o8 o8. 28 o8. 18 . . . . . . . . . . . . . .3~:owo:.:2:a .2: ooS w 2o. o8. o8. 2o 2o o8 So 2o. 2o. o8 . . . . . . . . . . . . .¢_Q@:QI:=@E§2: oz o o8. :8. 2o. 28 to :8 2o. 2o 2o So . . . . . .....B>QEE .2522: oEu S 8o. o8 S8. o8. :8 28 o8. 2o 8o. o8 . . . . . . . . . . . ... ....__se ofiéofioo .2: o2 8§Ewo:o$o=m .2: ooS H S2 o8“ S2 S2 S2 _ S2 S2 _ S2 S2 _ S2 . 05w 8Q 20523.5‘ dZ gunk/cu c0300 cofioo Eco Eco 8E wvfifiofl @3305 mQOSCUQOU wvntfiom mSOZGMHCOU hmmfl .232 wan 6N2 <82 E woooozoo mow “o wuEEmw E 22w 02.52252 13.0w we ommwcwohomléfi oEwP CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 23 ithe yield of continuous cotton in 1927, the coefficient of correlation be- ing .645 1.125, as shown in Table 13. In 1926, however, the correla- tion was not significant. The amount of phosphoric acid was signifi- cantly correlated with the average nitrifying power of the soil under continuous cotton and under cotton grown in rotation in 1927 (Table 13) and under continuous corn in 1926 and 1927 (Table 14). Hydrogen Ion Concentration The hydrogen ion concentration (pH value) of the soil was deter- mined by the colorimetric method, using La Motte indicators to develop the color. In this work the ratio of soil to water was 1 to 5. Twenty grams of soil were weighed out, placed in Erlenmeyer flasks, and 100 cc. of distilled water having a pH of 6.6 to 6.8 was added. The flasks were then shaken vigorously, stoppered, and the soil allowed to settle over night. Usually perfectly clear solutions were obtained in this IHEIHHGI‘. Table 12.——Hydrogen ion concentration (pH value) of soil samples collected under the crops May 18, 1927 Plat Continuous Rotated Continuous Rotated Rotated No. Treatment per acre corn corn cotton cotton cowpeas pH pH pH pH pH 1 200 lbs. superphosphate, 100 lbs. cottonseed meal. 6.5 6.3 6.5 6.5 6.4 2 Crop residues removed. . .. 6.5 6.5 6.6 6.6 6.4 3 No trcatment—check..... 6.5 6.6 6.4 6.6 6.4 4 200 lbs. superphosphate. .. 6.5 6.6 6.5 6.5 6.5 5 4tons manure . . . . . . . . . .. 6.5 6.3 6.6 6.5 6.5 6 No treatment—-check..... 6.3 6.3 6.6 6.5 6.5 7 200 lbs. supcrphosphate, 4tons manure . . . . . . . .. 6.4 6.4 6.4 6.4 6.4 8 107 lbs. rock phosphate. . . 6.4 6.2 6.3 6.4 6.4 9 107 lbs. rock phosphate, lltonsmanure . . . . . . . . .. 6.4 6.0 6.5 6.5 6.2 1O No treatment—check. . . .. 6.2 6.0 6.2 6.4 6.2 The pH values were determined on samples taken from the various plats in May, June, July, and August, 1927. Since the results obtained during each of the four months were quite similar, only the pH values of the samples taken in May are given here (Table 12). The highest pH value in May was 6.6 and the lowest pH value was 6.0, which oc- ‘curred on Plats 9 and 10 of rotated corn. In general the soil on Plat 10 of each of the blocks had a low nitrifying power in 1926 and 1927 (Tables 7 and 8), which may possibly have been due to the greater hydrogen ion concentration. Apparently the fertilizer treatments used had no consistent or appre- ciable effect on the hydrogen ion concentration of the soil. These re- sults, in general, agree with the work of other investigators. STATISTICAL ANALYSIS OF THE DATA While the relation of the various chemical and microbiological factors .among themselves and their bearing on the yield of crops may be shown 24 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION by graphs and curves, it is believed that these relationships can be shown ..; better by the use of statistical methods. Accordingly, the coefficient of P correlation existing between the several pairs of factors studied was cal- ; culated. In this connection it may be pointed out that the literature i does not contain much data on the statistical analysis of the chemical g and microbiological factors of soil fertility and the relation of these factors among themselves and to the yield of crops. Recently, however, .1 McCall and Wanser (16) in a study of summer fallow tillage in Wash- ington used the statistical method in the interpretation of their data. _ They found significant positive correlation between the amount of nitrates in the soil and the yield of wheat, between the moisture con- 1 tent of the soil and the yield of wheat, and between the amount of ii nitrates in the soil and the protein content (quality) of wheat. As mentioned previously, data were secured on (a) the amount of i. nitrates in the soil under the growing crops, (b) the nitrifying power of the soil, (c) the total nitrogen, (d) the total phosphoric acid, (e) the active phosphoric acid, and (f) the hydrogen ion concentration (pH value) of the soil. Coefficients of correlation between the several pairs of factors were computed according to the method of Wallace and Snedecorz for machine calculation. The correlation coefficients reported are based on only ten observa- tions for each pair of characters, since there were but ten plats of each crop grown. While significant correlations have been obtained in many cases, they should be regarded as indicating the probability rather than the certainty of the relationship of the several characters on account of the small numbers involved. The data have been analyzed with these limitations in mind. Correlation Data Obtained on Cotton The yield of cotton was positively correlated with the nitrate content, with the nitrifying power, with the total nitrogen, and with the total and active phosphoric acid of the soil (Table 13). The coefficient of correlation between the yield of continuous cotton and the amount of nitrates in the soil under the crop in May was .646 i124 in 1926 and .706 1.107 in 1927, both of which are significant. Positive correla- tion also was found between the yield of continuous cotton and the average amount of nitrates in the soil during the season, the correla- tion being .552 1.155 in 1926 and .700 1.109 in 1927. The average nitrifying power of the soil during the season apparently was a better index of the productiveness of the soil than the other factors studied. For example, the coefficient of correlation between the yield of continu- ous cotton and the average nitrifying power of the soil was .746 11095 in 1926 and .789 1.081 in 1927'. In the case of cotton grown in rota- tion the coefficient of correlation was .833 1:065 in 1926 and .829 $.06’? in 1927. - a 2H. A. Wallace and George W. Snedecor, “Correlation and Machine Cal- culation,” Iowa State College, Ames, Iowa, 1925. CHEMICAL AND MICROBIOLOGICAL 8TUDY OF LUFKIN SANDY LOAM 25 While the yield of cotton was positively correlated with the total. amount of nitrogen, with the total phosphoric acid, and with the active phosphoric acid of the soil, in most cases the correlation was not signifi- cant (Table 13). Table 13.—Coefficients of correlation between chemical and microbiological factors , and yield of cotton Continuous cotton Rotated cotton Pairs of characters 1926 1927 1926 1927 Yield and nitrates in May . . . . . . . . .. .646 i. 124 .706i. 107 .415i. 177 .600i. 137 Yield and average amount of nitrates. . 552 i. 155 . 700 i . 109 . 491 i. 162 . 3'89 i . 181 Yield and nitrifying power in May. . . . Yield and average nitrifying power. . . . 746 i . 095 .789 i . 081 . 833 i .065 . 829 i.O67 Yield and total P205 . . . . . . . . . . . . . .. .416i.177 .645i.125 .417i.177 .346i.188 Yield and total N . . . . . . . . . . . . . . . .. .444 i. 171 .639 i. 126 .776 i.085 .446 i. 171 Yield and active P205 . . . . . . . . . . . . .. .447 i. 171 . . . . . . . . . . .. .426 i. 175 . . . . . . . . . . . . Total N and average amount of nitrates . . . . . . . . . . . . . . . . . . . . . . . .841 i . 063 . 926 i. 302 . 405 i . 178 . 148 i . 167 Total N and nitrifying power in May. .382 i . 182 .221 i .203 .667 i. 119 . 134 i.210 Total N and average nitrifying power. . 641 i. 126 .347 i. 188 .789 i.080‘ . 184 i . 206 Averlggg nitrifying power and total - 2 5 . . . . . . . . . . . . . . . . . . . . . . . . . Average nitrifying power and active P205 . . . . . . . . . . . . . . . . . . . . . . . . . The total nitrogen in the soil was positively correlated with the amount of nitrate nitrogen in the soil and with the nitrifying capacity of the soil. The correlation between the amount of total nitrogen in the soil under continuous cotton and the average quantity of nitrates in the soil during the season was .841 i.063 in 1926 and .926 i302 in 1927. The nitrifying power of the soil was correlated with the total amount of phosphoric acid and the active phosphoric acid although the correla- y tion was not significant in all cases (Table 13). Correlation Data Obtained on Corn The yield of corn was correlated with the average nitrifying power of the soil, as shown in Table 14. In the case of corn grown on the same land every year the coefficient of correlation was significant, being .742 i.096 in 1926, and .658 i.121 in 1927. The yield of corn grown in rotation in 1927, however, ‘was not correlated with the nitrifying power of the soil, either in May or with the average of the season. The total nitrogen, the total phosphoric acid, and the active phos- phoric acid were not significantly correlated with the yield of either continuous or rotated corn. The percentage of total nitrogen was posi- tively and significantly correlated with the average amount of nitrates in the soil, except in the case of rotated corn in 1926 (Table 14). The coefficient of correlation between the average nitrifying capacity and the amount of nitrogen in the soil under continuous corn was .591 i139 in 1926 and .694 i.111 in 1927. In the case of rotated corn, the coefficient of correlation probably was not significant in 1926 2s BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION or in 1927. Significant positive correlation was found between the nitrifying power and the total phosphoric acid in the soil under con- tinuous corn but no such relation was found to exist in the soil under rotated corn. The active phosphoric acid also was significantly corre- lated with the nitrifying power of the soil under both rotated corn and continuous corn in 1926, the coefficient of correlation being .603 i136- and .584 i141, respectively. Table Dir-Coefficients of correlation between chemical and microbiological factors and yield 0f corn Continuous corn Rotated corn Pairs of characters 1926 1927 1926 1927 Yield and nitrates in May. . . ._ . . . . . . 280 i 197 .149 :1:.209 r‘ $O4i.159 —.741 i.096 Yield and average amount of nitrates. 051 i 213 —.O26 i 213 — 313 i. 192 —.781 i.083 Yield and nitrifying power in May. . . 322 i 191 .386 i 182 797 i 078 .042 i 213 Yield and average nitrifying power. . . 742 i 096 658 i 121 576 i 143 .192 i 206 Yield and total P205 . . . . . . . . . . . . . . . 209 i 204 201 i 205 — 393 i 182 —.284i 196 Yield and total N . . . . . . . . . . . . . . . . . . 229 i 202 122 i 204 347 i 188 —.469 i 166 Yield and active P205 . . . . . . . . . . . . . . 147 i 209 . . . . . . . . . . . . 188 i 206 . . . . . . . . . . . - Total N and average amount of nitrates . . . . . . . . . . . . . . . . . . . . . . . 981 i 008 926 i 030 362 i 185 524i 155 Total N and nitrifying power in May. 844 i 041 904 i 038 416 i 170 — 167 i 154 Total N and average nitrifying power. 591 i 139 694 i 111 488 i 163 — 355 i 187 Average nitrifying power and total P205..._.., . . . . . . . . . . . . . . 545i 150 653i 123 099i 211 418i 176 Average nitrifying power and active P205 . . . . . . . . . . . . . . . . . . . . . . . .. 584 i 141 . . . . . . . . . . .. .603 i. 136 . . . . . . . . . . . . DISCUSSION OF RESULTS The kind of crop and cropping system had distinct effects on the accumulation of nitrates in the field soil. The soil under rotated cot- ton contained the largest amount of nitrates during the seasons of 1925 and 1927’, but the soil under rotated corn contained the largest average amount for the three years, which was due to the greater accumulation of the nitrates in the soil in August and September, 1926, after the corn had matured and ceased taking up nitrates. The soil under con- tinuous cotton and under continuous corn contained significantly smaller quantities of nitrates than the soil under cotton and corn grown in rotation. This fact indicates that the growing of cotton or corn on the same land every year has a depressing, or injurious, effect on the accumulation of nitrates in the soil. Nitrate production, or accumulation of nitrates, in field soil under cotton gradually increased as the season advanced, reaching a peak in July and decreasing thereafter. It follovred a similar course in the soil under corn, except the greatest accumulation occurred a month later, in August. The greater accumulation under corn apparently was due to the fact that the corn having matured ceased absorbing nitrates dur- ing the latter part of July and conditions during August were favor- able for nitrification, conditions which were conducive to the accumu- lation of nitrates. e11~in~m35 ‘ - m, .» _ -* CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 27 The season, that is, the date of sampling, apparently had no consist- ent influence on the nitrifying power of the soil under laboratory con- ditions. The growing of corn on the same land every year, however, had a tendency to lessen the power of the soil to produce nitrates, since the soil under continuous corn did not nitrify ammonium sulphate as rapidly as the soil under the other crops. This fact apparently ex- plains why the yield of corn is reduced more by continuous cropping than is the yield of cotton. The application of nitrogen, in the form of cottonseed meal and manure, and of phosphoric acid, as superphosphate or ground rock phos- phate, increased the production of nitrates in the field soil and stimu- lated the nitrifying power of the soil. In fact, the_treatment of 200 pounds of superphosphate and 4 tons of manure per acre brought about the greatest accumulation of nitrates in the field and the most vigorous nitrifying capacity of the soil in the laboratory. These results are in general agreement with those of other Workers. In studying the nitrifying power of the soil, ammonium sulphate was used as the source of nitrogen. In one series the ammonium sulphate was used‘ alone and in another with lime to keep the reaction basic. Lime increased the nitrifying capacity of the soil, since the soil which received lime produced about six times as much nitrate nitrogen as the soil which received no lime. These results are similar to the results reported by Erdman and Humfeld (Iowa Agricultural Experiment Sta- tion Research Bulletin 110, 1928.). The use of the statistical method in the interpretation of the data revealed some interesting results and indicated certain relationships that were not apparent before the correlations were made. The yield of cot- ton was significantly correlated with the amount of nitrates in the soil under the growing crop and with the nitrifying power of the soil. The nitrifying capacity of the soil was a better single index of the produc- tiveness of the soil than the other factors studied. These results are in accord with those of Brown (5, 6, '7, 8), Burgess (9), Gainey and Gibbs (11), and Waksman (22). Regarding nitrification as an in- dicator of productiveness, Burgess (9) stated, “In fact it is probably the best single test of any description yet developed for ascertaining the comparative crop-producing power of arable soils.” The yield of cotton was positively correlated with the total nitrogen, with the total phosphoric acid, and with the active phosphoric acid of the soil, but in most cases the correlation was not significant. The nitrifying power of the soil was correlated with the total and active phosphoric acid, although the correlation was not significant in all cases. In general the results obtained with cotton were better indicators of productiveness of the soil than the results obtained with corn. Statistical methods have not been used extensively in the interpreta- tion of soil fertility and soil microbiological data, especially the rela- tion of these factors to the yield of crops. It is believed, however, from the results reported in this Bulletin, that a more extensive use of statis- 28 BULLETIN NO. 421, TEXAS AGRICULTURAL EXPERIMENT STATION tical methods is justified, since they are valuable in the interpretation i ’ of data and often permit of more definite conclusions than would other- I wise be secured. SUMMARY In a chemical and microbiological study of Lufkin fine sandy 10am f soil in 1925, 1926, and 1927 at the Texas Agricultural Experiment A Station, College Station, Texas, the nitrifying power of the soil was a correlated positively and significantly with the yields of cotton and" corn. The nitrifying capacity of the soil was a better index of the pro- i ductiveness of the soil than any other factor studied. The nitrifying power of the soil was also positively correlated with the total nitrogen, . with the total phosphoric acid, a11d with the active phosphoric acid of . the soil. The nitrifying capacity of the soil in the laboratory was not affected by the season, as indicated by the analyses of samples taken at different times during the growing season. The growing of corn on the same land every year had a tendency to weaken the nitrifying capacity of i- the soil. The application of nitrogenous materials, cottonseed ‘meal and i manure, and of phosphoric acid, as superphosphate or ground rock phos- phate, increased the production of nitrates in field soil and stimulated the nitrifying power of the soil. Under conditions in the laboratory ‘ the addition of lime increased the capacity of the soil to produce nitrates, since the soil that received lime produced about six times as much nitrates as the soil that received no lime. This increased nitrify- ing power, however, was not more significantly correlated with the yield of cotton and corn than was the nitrifying power of the soil without lime. The continuous growing of cotton and of corn decreased the produc- tion of nitrates in field soil. The accumulation of nitrates in the soil gradually increased as the season advanced, reaching a peak in July in the soil under cotton and in August in the soil under corn, and decreasing thereafter. The results obtained with the statistical method in this study indi- cate that the method could be used more extensively than it is at present, since its use permits of more definite conclusions than would be ob- tained otherwise. LITERATURE CITED (1) Albrecht, W. A. 1919. Nitrate production in soil as affected by crops and cultivation. Mo. Agr. Exp. Sta. Bul. 163, pp. 67-68. (2) Albrecht, W. A. 1925. Effects of different soil treatments, long continued, upon bacterial activity in the soil. yMo. Agr. Exp. Sta. Bul. 228, pp. 81-82. (3) Allen, E. R. 1916. Nitrification. Ohio Agr. Exp. Sta. Monthly Bul. 1, pp. 153-154. CHEMICAL AND MICROBIOLOGICAL STUDY OF LUFKIN SANDY LOAM 29 (4) Baldwin, I. L., Nichter, W. J ., and Lindsey, R. O. 1923. Nitrate studies on Purdue rotation field No. 6. Ind. Acad. Sci. Proc. 39:269-280. (Abstract in Exp. Sta. Rec. 52:816.) (5) Brown, P. E. 1912. Bacteriological studies of field soils. II. The effects of continuous cropping and various rotations. Iowa Agr. Exp. Sta. Res. Bul. 6. (6) Brown, P. E. 1913. Bacteriological studies of field soils. III. The effects of barnyard manure. Iowa Agr. Exp. Sta. Res. Bul. 13. (7.), Brown, P. E. 1915. Bacterial activities and crop production. Iowa Agr. Exp. Sta. Res. Bul. 25. x (8) Brown, P. E. 1916. Relation between certain bacterial activities in soils and the crop-producing power. Jour. Agr. Res. 5: 855-869. (9) Burgess, P. S. 1918. Can we predict probable fertility from soil biological data? Soil Science 6:449-462. (10) Fraps, G. S. 1909. Active phosphoric acid and its relation to the needs of the soil for phosphoric acid in pot experiments. Tex. Agr. Exp. Sta. Bul. 126. (11) Gainey, P. L. and Gibbs, W. M. 1916. Bacteriological studies ty-five years. Jour. Agr. Res. 6:953-975. (12) Hall, T. D. 1921. Nitrification in some South African soils. Soil Science 12:301-363. (13) Harper, H. J . 1924. The accurate determination of nitrates in soils. Ind. and Eng. Chem. 16:180-183. - (14) Karraker, P. E. 1927. Nitrates and wheat yields after certain crops. Soil Science 24:247-258. (15) Lyon, T. L. and Bizzell, J . A. 1913. Some relations of certain higher plants to the formation of nitrates in soils. New York (Cornell University) Agr. Exp. Sta. Memoir No. 1. (16) McCall, M. A. and Wanser, H. M. 1924. The principles of summer-fallow tillage. Wash. Agr. Exp. Sta. Bul. 183'. (17) Martin, F. J . and Massey, R. E. 1923'. Nitrification in Sudan soils. Wellcome Trop. Research Labs., Chem. Sec. Pub. 29. (Abstract in Exp. Sta. Rec. 50:816.) (18) Murphy, H. F. 1925. Nitrate studies on a manured and un- manured soil under continuous wheat culture. J our. Amer. Soc. Agron. 17:734-741. 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