Plants as Affected by Insufficient Food. 155 



c Deposits from the atmosphere in rain or snow 



(260). 



d Ammonium salts or nitrates applied to the soil 

 (261). 



256. The Conditions Affecting Nitrification are sim- 

 ilar to those affecting plant life in general, since nitri- 

 fication results from plant life. As it takes place be- 

 low the surface of the soil, it is favored by the same 

 conditions that favor the root growth of land plants, 

 viz., aeration, warmth and moisture. In general, it is 

 active during the growing season, but at a standstill 

 during the dormant period. It does not proceed rap- 

 idly in spring until the soil has become sufficiently 

 warm to promote active root growth. 



Nitrification also releases the other food materials 

 contained by organic matter (92). 



257. Soil Aeration Promotes Fertility by favoring 

 nitrification. Thus cultivation and drainage (of heavy 

 soils) not only directly promote the growth of plants 

 by assisting aeration (93), but they actually increase 

 plant food. Early plowing in spring promotes nitrifi- 

 cation by favoring warming of the soil. Cultivation 

 in dry weather further promotes plant nutrition by 

 preventing the accumulation of soluble plant food in 

 the dry surface soil, where it is deposited above the 

 reach of roots through evaporation. 



258. Partially-Decomposed Organic Manures Act 

 More Promptly than fresh ones, because nitrification 

 has already commenced in these material. 



