NITROGEN, NITRIFICATION, NITROGENOUS MANURES 145 



fication. A fallow is beneficial to a succeeding crop 

 because of the nitrogen which is rendered available. 

 If a soil is rich in nitrogen and lime, summer fallow- 

 ing causes the production of more nitrates than can be 

 retained in the soil. The crop utilizes only a part of 

 the nitrogen rendered available, the rest being lost by 

 drainage, ammonification, and denitrification. Hence 

 the available nitrogen is increased while the total nitro- 

 gen is greatly decreased. 9 



The gain of 0.002 per cent of soluble nitrogen was 

 accompanied by a loss of 0.012 per cent of total nitro- 

 gen. For every pound of available nitrogen there was 

 a loss of six pounds. Bare fallowing of land for an 

 entire year should not be practiced, except occasionally 

 to destroy weeds or insects, as it results in permanent 

 injury to the soil. A short period of fallow and the 

 practice of green manuring with leguminous crops both 

 enrich the soil with humus and nitrogen, and improve 

 the physical properties. 



162. Influence of Plowing upon Nitrification. In a 



rich soil containing the necessary alkaline matter, nitrifi- 

 cation goes on very rapidly. This is one reason why 



