Relations of Higher Plants to the Formation of Nitrates 13 



content of the soil under these crops ranged from 24.1 per cent for maize 

 to 26.6 per cent for wheat. The difference in nitrate content, therefore, 

 could not be attributed to differences in soil moisture. 



In all these experiments nitrates reached their lowest point under grass 

 before they did under wheat or oats, and under wheat and oats before 

 the}'' did under maize; but even after the minimum nitrate content was 

 reached under all crops they stood in the same order. As these experi- 

 ments represent soils in Germany, New Jersey, Pennsylvania, Wisconsin, 

 and Utah, thus ranging from a humid to an arid region, the agreement in 

 the relation of the nitrogen content of the soil to the plants used in the 

 experiments is certainly significant. 



■ Experimetits showing higher nitrate content under -plants than 



in fallow land 



The figures given by Stewart and Greaves (1909), in a study of nitrates 

 in irrigated soils planted to maize, potatoes, and alfalfa, and also on land 

 fallow during a period of three years and planted to oats one year, show 

 nitrates to be higher under maize than in fallow land at certain stages in 

 the growth of the crop, and in some cases the same was true with potatoes. 

 The highest nitrate content under these crops occurred at about the time 

 of their most active growth and in the first foct or the first two feet of soil. 



King and Whitson (1902) report an experiment in which one of two 

 contiguous plats of oats had a crop entirely removed on June 20, on which 

 date determinations of nitrates were made in the soil of both plats to a 

 depth of four feet. The crop on the harvested plat was weighed and the 

 dry matter determined. At the end of nineteen days nitrates were 

 again determined in both plats, the remaining oats were harvested and 

 weighed, and the dry matter was determined. No determinations of nitro- 

 gen were made with the crop, but the gain in nitrogen for the nineteen 

 days was calculated from the drj^ weight on the basis of average analyses for 

 oat plants at that stage. The gain in nitrogen in the oat plants which had 

 been growdng for nineteen days, minus the loss of nitrates during that time, 

 was twice as great as could be accounted for by the gain of nitrates on the 

 bare plat. No account was taken of the nitrogen in the plant roots, which 

 would make a still greater difference. Evidently there was a much larger 

 supply of available nitrogen in the soil growing, oats than was represented 

 by the nitric nitrogen of the bare plat, and this supply was due either to a 



