^^1®1 FEBLD CBOPS. 833 



about 1,400 lbs. and the hydrochloric acid-soluble 9.800 lbs. The total nitrogen 

 found in the same depth of soil was 8,240 lbs. While the nitrogen was not con- 

 sidered remarlsably high, it was shown that a very considerable portion of it 

 actually existed in the soil in the form of nitric nitrogen at the time of planting, 

 the upper 2 ft. containing nitric nitrogen equivalent to 211 lbs. of sodium nitrate! 



The power of this soil to fix nitrogen was discussed in previous publications 

 (E. S. R., 25, pp. 814, 815). It was found at that time that in 27 days a sample 

 of this soil simply Ijept in a moderately warm room gained 4.82 mg. of nitrogen 

 for each 100 gm. of soil, or 48 parts per million; this was equivalent to the 

 addition of 192.8 lbs. of nitrogen or of about 1,100 lbs. of sodium nitrate to an 

 acre-foot of soil in one month. 



In both seasons the effects of irrigation on the distribution of the nitrates were 

 determined. On April 29, 1913, before irrigation, a soil sample in the upper 

 4 ft. was found to contain nitric nitrogen etiuivalent to 1,908 lbs. of sodium 

 nitrate, while another sample taken the same day from the same depth of soil 

 contained the equivalent of 471 lbs., but with a total additional equivalent of 

 721 lbs. in the seventh, eighth, and ninth foot. On June 27, 13 days after irriga- 

 tion, the upper 4 ft. of three different sections of soil were found to contain 162, 

 91, and 156 lbs., respectively, with a maximum of 30 lbs. below 4 ft. in three 

 borings talien to a depth of 12 ft., and a minimum of zero. The season of 1913 

 had a high rainfall in general, but with long periods witiiout any precipitation, 

 while in 1915 the total rainfall was as large again and well distributed in a suc- 

 cession of light showers throughout the season. Soil samples taken at the end 

 of June, 1915, were found to contain, even in the fourth foot, nitric nitrogen as 

 high as equivalent to 48 lbs. of sodium nitrate, while by August 3, at the begin- 

 ning of the ripening of the grain, the surface foot contained the equivalent of 

 only about 20 lbs., the minimum found in the fourth foot at this time being zero. 

 Samples taken from fallow ground on August 3, 1915, showed a nitric nitrogen 

 content equivalent to 285.5 lbs. of sodium nitrate, while a sample from cropped 

 land taken to the same depth at the same time gave an equivalent of 46.9 lbs. 

 " The crop, either by preventing the formation of the nitrates or by using them 

 up, had made a difference equal to 238.6 lbs. of sodium nitrate in this depth of 

 soil." 



Investigations showing the nitrifying efficiency of this soil have been pre- 

 viously noted (E. S. R., 25, p. 814; 30, p. 818). Three sets of soil samples 

 taken from fallow land to a depth of 19 in. on August 1, 1913, showed a 

 nitric nitrogen content equal to 542.43 lbs. of sodium nitrate per acre. The 

 nitric nitrogen of samples taken the same date from cropped land to a depth 

 of 2 ft. corresponding to 101.2 lbs., and samples taken December 4, 1914, to a 

 depth of 19 in. on the same plat, after harvesting a crop of wheat August 6, 

 irrigating the land August 28, and plowing it November 14, gave an equivalent 

 of 299.35 lbs. It is pointed out that the difference in nitric nitrogen as com- 

 pared with the fallowed land was equal to 243 lbs. of sodium nitrate in favor 

 of the latter, and that the difference between 299.35 lbs. and 101.2 lbs. of 

 sodium nitrate gives an approximation to the difference in the amount of 

 nitric nitrogen in the upper 2 ft. of soil on August 1 and December 4. Studies 

 along this line more closely followed in 1915 gave similar and equally positive 

 results. The cropped land again contained its minimum amount of nitric 

 nitrogen about August 1. Data arranged in tables indicate a rapid fall of the 

 nitric nitrogen in the cropped land from the middle of May to the beginning of 

 August, or during the growing period of the plant. 



The total nitrogen was also determined and the data secured are given in 

 tables, without interpretation of the results because of the difficulty of obtain- 

 ing samples of soil varying by less than the amount of nitrogen concerned In 



