418 THE PRINCIPLES OF SOIL MANAGEMENT 



The amount of nitrogen removed by the maize 

 crop was greater than that removed by the timothy, 

 consequently the greater amount in the former soil 

 can not be due to the effect of the crop. 



So far as the> conservation of nitrogen is concerned, 

 sod is an ideal crop, for nitrates are formed very little 

 faster than they are used, and are not carried off in 

 large amounts by the drainage water. 



In the corn land as much as 500 pounds of nitrates 

 were present in the first twelve inches of one acre, or 

 fully five times as much as was used by the crop. 



284. Depth at which nitrification takes place. 

 Warington concluded from his experiments that 

 nitrification takes place only in the surface six feet of 

 soil. Hall has pointed to the fact that no more nitrates 

 were leached from the 60-inch lysimeter at Rotham- 

 sted than from the one 20 inches deep; which is very 

 good evidence that in that particular soil nitrification 

 does not take place below 20 inches from the surface. 

 In more porous soils, however, nitrification probably 

 extends deeper, especially in the rich and porous 

 subsoils of the arid and semi-arid regions. 



In all probability, nitrification is largely confined 

 to the furrow slice, where the opening up of the soil 

 by tillage has provided the necessary air, and where the 

 temperature rises to a point more favorable to the action 

 of nitrifying bacteria. The results from the aerated 

 and unaerated soils cited above represent the differ- 

 ences that doubtless exist between the furrow slice and 

 the subsoil so far as nitrification is concerned. 



285. Loss of nitrates from the soil. Nitrogen hav- 



