CHAPTER XI 



NITROGENOUS FERTILIZERS • 



We have seen that nitrogen exists in soils in several differ- 

 ent forms, as organic matter, ammonia and nitrates, and that 

 it msiy be transformed from one to another of these, depend- 

 ing on the conditions that obtain in the soil itself. Ferti- 

 lizers used for their nitrogen may have this nitrogen present 

 in any one or more of these forms, and when incorporated 

 with the soil, transformation will proceed according to the 

 same laws that govern the soil nitrogen. This is important 

 because nitrogen is more readily used by crops in some 

 forms than in others. 



197. Relative quantities of the different forms of nitrogen 

 in soils. — One would naturally expect to find the greater 

 part of the supply of soil nitrogen in the most stable forms, 

 and this is, in fact, the case. The uncombined nitrogen of the 

 air constitutes the largest supply because of its diffusibility 

 with the atmospheric air. Next in quantity is the nitrogen 

 of organic compounds, ranging from 0.05 to 0.3 percent or 

 1000 pounds to 6000 pounds to the acre in the furrow slice 

 of ordinary arable land and slightly, but appreciably, soluble 

 in water. In upland cultivated soils the nitrogen of nitrate 

 salts forms the next largest supply, but rarely exceeds 20 

 percent of the total combined nitrogen of the soil. 



In inundated soils, the nitrogen of ammonia salts and 

 nitrites forms a larger proportion of the soil nitrogen than 

 does the nitrate nitrogen, but in well-aerated soils these com- 

 pounds exist in very small quantities. 



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