454 SOILS: PROPERTIES AND MANAGEMENT 



that particular soil nitrification does not take place below 

 40 inches from the surface. In more porous soils, how- 

 ever, nitrification probably extends deeper, especially 

 in the rich and porous subsoils of arid and semiarid regions. 



In all probability, nitrification is largely confined to 

 the furrow slice, where the opening-up of the soil by til- 

 lage has provided the necessary air, and where the tem- 

 perature rises to a point more favorable to the action 

 of nitrifying bacteria. The results from the aerated and 

 unaerated soils as shown above represent the differences 

 that doubtless exist between the furrow slice and the sub- 

 soil so far as nitrification is concerned. 



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

 ing been converted into the form of nitric acid, it im- 

 mediately combines with available bases in the soil, 

 forming salts, all of which are very easily soluble and 

 which are carried in solution by the soil water. In a 

 region of much rainfall, the removal of nitrates in the 

 drainage water is very rapid. Hall 1 states that nitrates 

 formed during the summer or the autumn of one year are 

 practically all removed from the soil of the Rothamsted 

 fields before the crops of the following year have advanced 

 sufficiently to utilize them. It was formerly customary 

 to fertilize with ammonium salts in autumn, but the 

 drainage water showed on analysis such a large quantity 

 of nitrates during the months intervening between the 

 time of fertilizing and the opening of the growing season 

 that the practice was discontinued. 



In regions of less rainfall or of greater surface evapora- 

 tion, the loss in this way is less, reaching a minimum in an 

 arid region when irrigation is not practiced. Under 



i Hall, A. D. The Soil, p. 176. New York, 1903. 



