428 NATURE AND PROPERTIES OF SOILS 



The high nitrate accumulation under the maize is probably 

 due to the tillage and aeration which the soil received and 

 possibly to the direct stimulation of the crop on nitrification. 

 The low amounts of nitrate nitrogen in the grass land are 

 probably due, at least partially, to the influence of the sod in 

 encouraging nitrate assimilation by the soil organisms. The 

 nitrifying power of the sod soil is probably much greater 

 than the data just presented would lead one to suspect. Sodi- 

 um nitrate applied to grass at Cornell University was found 

 to be changed to other than the nitrate form very rapidly, 

 even when the amounts added were extremely large. This 

 rapid disappearance of the nitrate form of nitrogen is not 

 readily accounted for by cropping and drainage removal. 

 Such facts lend considerable plausibility to the suggestions 

 made above, regarding the encouragement which the synthetic 

 removal, especially of nitrates, receives from organisms when 

 the soil is under a grass crop. 



The synthetic removal of nitrates, nitrites, and ammonia 

 assumes considerable importance at certain times of the year. 

 It seems to be a natural means of conserving an important 

 soil constituent, since nitrate nitrogen is extremely soluble 

 and easily lost by drainage. ,The nitrogen thus affected is 

 changed to a more or less stable form, from which nitrates 

 may be produced during the following year. The use of a 

 cover-crop in an orchard during the late summer and fall is 

 often practiced. A disappearance of nitrates but not a loss of 

 nitrogen thus occurs and the trees are early forced into the 

 resting stage. 



235. Natural acquisition of nitrogen by the soil. — Since 

 all of the nitrogen now found in the soil was probably ac- 

 quired from the atmosphere, the natural forces which facili- 

 tate such a transfer assume considerable practical importance. 

 The more rapid the natural acquisition of nitrogen from the 

 air, the less serious will be the nitrogen problem in agricul- 

 tural practice. 



