In a paper read at the meeting last year it was pointed out that when a soluble form of organic matter was added to soils which were incubated in tumblers, a considerable quantity of nitrate nitrogen could be used by the micro-organisms of the soil. The amount of nitrate nitrogen assimilated was in a measure determined by the amount of nitrate present at the beginning, the form and amount of organic matter used, and the length of incubation period. Two percent of straw furnished sufficient carbon for the assimilation of 10 mgm. per 100 gms. of soil in one week, and for about 15 mgm. in 3 weeks. Two percent of soluble starch or dextrose permitted the assimilation of about 15 mgm. in 1 week

Pendleton, Ray A.

Smith, Frederick B.

English

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 37 Annual Issue Article 10 1930 Further Studies on the Nitrate Assimilating Power of Soils Ray A. Pendleton Iowa State College Frederick B. Smith Iowa State College Copyright ©1930 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Pendleton, Ray A. and Smith, Frederick B. (1930) "Further Studies on the Nitrate Assimilating Power of Soils," Proceedings of the Iowa Academy of Science, 37(1), 65-69. Available at: https://scholarworks.uni.edu/pias/vol37/iss1/10 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. FURTHER STUDIES ON THE NITRATE ASSIMI-LATING POWER OF SOILS RAY A. PENDLETON AND FREDERICK B.. SMITH 1 In a paper read at the meeting last year (3) it was pointed out that when a soluble form of organic matter was added to soils which were incubated in tumblers, a considerable quantity of nitrate nitrogen could be used by the micro-orga11isms of the soil. The amount of nitrate nitrogen assimilated was in a measure determined by the amount of nitrate present a:t the beginning, the form and amount of organic matter used, and the length of incu-bation period. Two percent of straw furnished sufficient carbon for the assimilation of 10 mgm. per 100 gms. of soil in one week, and for about 15 mgm. in 3 weeks. Two percent of soluble starch or dextrose permitted the assimilation of about 15 mgm. in 1 week. Murray (2) <tdded finely chopped straw to soils and noted the disappearance of nitrate nitrogen. He used SO mgm. per 100 gms. of soil with chopped straw in varying amounts from 0.5 percent to 5.0 percent. When lie used 2 percent of straw he noted a loss of 14.99 mgm. of nitrate nitrogen in 6 weeks and only 6.5 mgm. in 12 weeks. It is quite probable that if he had made his determina-tions at an earlier date he would have found a still larger loss. Meggett ( 1) in attempting to prevent large losses of nitrate nitrogen from the soil by leaching, applied sugar to the soil at periodic intervals during the summer· and found that it prevented the loss of nitrates. In his laboratory tests he found that when he added 1 percent of sugar to his soil in tumblers plus 10.5 mgm. of nitrate nitrogen per 100 gms. of soil (soil originally contained 13.2 mgm.), all of the nitrates disappeared in 7 days. In another test he found the same disappearance in 3 days. He found no loss loss of total nitrogen. Another point of- interest in his work was the acceleration of nitrification after the organic matter had been all used. In work of this nature it is important to keep this fact in mind, since it is desirable to make the determinations at the time when the nitrifiers are least active and the nitrate assimilators are most active. 1 The authors wish to express their appreciation of the assistance given by Dr. P. E. Brown by his helpful suggestions and reading of the manuscript. 65 1Pendleton and Smith: Further Studies on the Nitrate Assimilating Power of SoilsPublished by UNI ScholarWorks, 193066 IOWA ACADEMY OF SCIENCE In the fall of 1929 a quantity of soil was collected from 6 differ-ent soil types. This was potted into four-gallon stone pots in the greenhouse, using 3 pots of each type of soil. These pots were then numbered A, B, and C for each type and were given the following treatments: A - check; B - sodium nitrate at the rate of 200 lbs. per acre; and C - sodium nitrate a~ the rate of 200 lbs. and finely chopped dry straw at the rate of 2 tons per · acre. The soils were kept watered and fallow. From time to time samples were collected from each pot with a sampling tube so as to get a representative sample, and determinations made of the ni-trate content and the nitrate assimilating power. Some previous work on studying the methods of measuring the nitrate assimilating power by using 5, 10, 15, 20 mgm. of nitrate nitrogen per 100 gms. of soil had indicated that a greater amount might be used to advantage since the smaller quantities 'were assimi-lated rather quickly. Accordingly 25 mgm. was selected as the most desirable amount and this amount was used in the work reported here. It was also previously found that where a soluble form of organic matter was used, there seemed to be no advantage of extending the incubation period more than 2 weeks, at least unless II- much larger amount of nitrate nitrogen was used. Con-sequently it was planned to use 4 different incubation periods: 3 days, 1 week, 2 weeks, and 4 weeks. For the three-day and one-week periods dextrose was used at the rate of 1 percent as a source of carbon; for the two-week period starch was used at the rate of 1 percent; and for the four-week period, cellulose acetate at the rate of 1 percent. Parallel with this test another test was made in which the same amount of nitrate was added but no organic matter. In order to check the results and also to correlate them if possible with the original nitrate content of the soil, two sets of determinations were made using like methods. The first set was made shortly after the soils were potted when the nitrate content was moderately low and the second set later when the nitrate content had materially increased. The results of this work which were secured from two of the representative soil types are given in tables I and II. These data. portray very effectively the results secured from the whole series. The Calhoun silt loam is a poorer soil than the Carrington loam, i.e., a less productive soil naturally, and the difference appears to be more or less mirrored in the biological activities. The nitrate production was less and also the nitrate assimilating power showed 2Proceedings of the Iowa Academy of Science, Vol. 37 [1930], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol37/iss1/10THE NITRATE ASSIMILATING POWER OF SOILS 67 less potential possibilities. It appears, however, that when a soluble . form of organic matter was added to the soil the nitrate assimi-lating organisms were stimulated to such an extent that only small differences could be noted among the different soils. The accumulation of nitrates in the soil, without a correspond-ing increase in available carbon, seemed to cause a depression in the vigor of the nitrate assimilating organisms. This same ten-dency was noted in all of the soils tested. This can be best illus-trated from the data of the one-week incubation period. At the fir$t sampling, Dec. 15, the average nitrate content of the three pots of Carrington loam was 3.86 mgm. per 100 gms. of soil and the average amount assimilated when tested without the addition of organic matter was 5.88 mgm. Later, on Feb. 15, when the nitrate content had increased to 5.35 mgm., the amount assimi-lated under the same conditions dropped to -1.38 mgm., or an in-crease over the original content plus the 25 mgm. that had been added. In the Calhoun silt loam the average nitrate content on Dec. 15 was 1.57 mgm. and the average amount assimilated was 6.40 mgm. On Feb. 15 the average nitrate content was 2.36 mgm. and the average amount assimilated was 1.62 mgm. In each soil there was a rapid drop in the nitrate assimilating efficiency as the nitrate content of the soil increased, when tested without the use of organic matter. Also, at both elates of sampling the Calhoun silt loam showed a lower nitrate content and a higher nitrate assimi-lating power, when measured by this method, than did the Carring-ton loam. These same general tendencies were exhibited by the other soils. VVhen organic matter was added to the soils for incubation these differences \Vere largely ironed out and the Carrington loam by this method showed slightly higher nitrate assimilating power. It appeared also that it required some time for the nitrate to have any appreciable effect on the nitrate assimilating organisms. "When the soils were first potted the soils of B pots had a higher nitrate content due to the addition of fertilizer; yet this apparently had no effect on the nitrate assimilating organisms at the early sampling elates but did depress the nitrate assimilating power, when measured without organic matter, at the later elates of samp-ling. In the C pots, where chopped straw was added in addition to sodium nitrate, the nitrate content of the soils did not drop suffi-3Pendleton and Smith: Further Studies on the Nitrate Assimilating Power of SoilsPublished by UNI ScholarWorks, 1930Table I -Nitrate Assimilation Stud4es on Carrington Loam in the Greenhouse MGM. NOa - N. PER 100 GMs. OF DRY SOIL 3 DAYS INCUBATION 1 WEEK INCUBA'l'ION 2 WEEKS INCUBATION NO.-N. NO,-N. NO,-N. PoT TREATMENT ASSIMILA'l'ED ASSIMILATED ASSIMILATED NO, NOa+ NO, NO,+ NO, CoN- NO, CoN-NO, CoN-NO,+ NO, TENT DEX- ALONE, TENT DEX- ALONE TEN'!' STARCH AI.ONE TROSE TROSE Soil Sampled Nov. 28 Soil Sampled De-.. 15 Soil Sampled Jan. 6 Check 2.751 8.65 I 1.70 3.45112.91 l 6.15' 4.72113.67 1-1.23 Soil+NaNOa 3.21 10.57 2.41 4.76 13.74 7.06. 5.00 11.35 -2.80 Soil+ N aNO, +straw 3.70 10.15 3.05 3.45 13.40 4.45 4.35 12.10 -1.25 Soil Sampled Jan. 25 Soil Sampled Feb. 15 Soil Sampled Feb. 4 Check 6.451 9.90 I 0.20 4.95112.15 1-0.75 5.88111.68 1-2.47 Soil+NaNOa 7.14 12.29 0.29 5.95 12.30 -1.6~·1 7.36 14.76 -3.89 Soil+ N aNOa +straw 6.76 10.56 2.81 5.15 9.60 -1.75 6.34 11.04 -2.96 Table II -Nitrate Assimilation Studies on Calhoun Silt Loani in the Greenhoiise MGM. NO, - N. PF,R 100 GMS. 01" DRY SOIL 3 DAYS INCUBATION 1 WEEK INCUBA'I'ION 2 WEEKS INCUBATION NO,-N. NO,-N. NO,-N. PoT TREATMEN'l' ASSIMILATED ASSIMILATBD ASSIMILATED NO, NOa+ NO, NOa+ I NO NO, CoN- NO, CoN- CoN-NO,+ NO, DEX- DEX- 3 TEN'l' ALONE TF,NT TROSF, AI.ONE TENT STARCH ALONE TROSE Soil Sampled Nov. 28 Soil Sampled Dec. 15 Soil Sampled Jan. 6 Check 0.50 110.49 I 5.50 0.50 111.05 I 6.10 1.331 9.63 1-1.47 Soil+ NaNOa 2.74 9.79 4.74 2.55 11.10 7.55 2.63 11.53 0.28 Soil+ NaNO,+ straw 3.30 ' 11.85 4.95 1.66 ' 11.01 5.56 1.56 8:71 -0.44 Soil Sampled Jan. 25 Soil Sampled Feb. 15 Soil Sampled Feb. 4 Check 1.891 7.94 I 2.39 2.06 , 11.21 I 2.01 2.331 4.43 1--0.52 Soil+NaNOa 3.25 8.90 3.75 3.09 12.94 .I.59 3.78 6.78 -0.42 Soil+ N aNOa +straw 2.22 8.72 3.17 1.96 11.21 1.26 2.23 8.43 1.03 4 WEEKS INCURATION NO,-N. ASSIMILATED NO, NO,+ CoN- CFLLU-NOa TENT LOSB ALO NB ACETATE Soil Sampled Jan. 10 4.721 2.22 I 0.52 5.88 3.38 1.68 4.67 2.47 0.47 Soil Sampled Jan. 31 6.421 2.52 I 0.92 6.94 2.84 1.24 5.42 1.82 1.02 4 WEEKS INCUBA'l'ION NO,-N. Assnm,ATED NO. NO,+ CoN- CitLLU-NO, 'l'I;NT LOSE ALONE ACETA'l'E Soil Sampled Jan. 10 1.841 0.24 I 0.89 3.12 0.62 0.27 2.30 2.90 1.00 Soil Sampled Jan. 31 1.971 3.27 I 2.72 3.45 3.45 2.15 2.08 2.83 3.28 O' 00 1--< 0 ~ > > 0 > tj M ~ ><: 0 >rj ff) (} @ ~ (} M 4Proceedings of the Iowa Academy of Science, Vol. 37 [1930], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol37/iss1/10THE NITRATE ASSIMILATING POWER OF SOILS 69 ciently to have much effect. Consequently the results from these soils was not materially different from that of the untreated soils. LITERATURE CITED (1) MBGGI1"l', A. A. 1922. Studies on an acid soil in Assam. IL Memoirs India Agric. Department Chemical Series 7: 31-53. (2) MURRAY, T. J. 1921. The effect of straw on the biological soil processes. Soil Sci. 12 : 233-259. (3) PENDLETON, R. A. and SM!l'H, F. B. 1929. Studies on methods of measuring the nitrate assimilating power of soils. Proc. Iowa Acad. Sci. 36 : (in press) IowA STATE CoLLEGE, AMES, IowA. 5Pendleton and Smith: Further Studies on the Nitrate Assimilating Power of SoilsPublished by UNI ScholarWorks, 1930

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