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 simi- 

 lar 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 dur- 

 ing the dormant period. It does not proceed rapidly in 

 spring until the soil has become sufficiently warm to pro- 

 mote active root growth. 



Nitrification also releases the other food materials con- 

 tained 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 pre- 

 venting 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 materials. 



