126 SOILS AND FERTILIZERS 



the essential organisms which assist the crops to 

 obtain their nitrogen. For example, if clover is 

 grown on new land, the soil is liable to be deficient in 

 the organisms which assist in the assimilation of 

 nitrogen and which are present in the root nodules of 

 the plant. If these organisms are supplied, better 

 conditions for growth exist. The extent to which it 

 is necessary to inoculate soils with organisms for the 

 assimilation of nitrogen, has not yet been determined 

 by actual field experiments. 



147. Loss of Nitrogen by Fallowing Rich Lands. 



— Summer fallowing creates conditions favorable to 

 nitrification. A fallow is beneficial to a succeeding 

 crop because of the nitrogen which is rendered avail- 

 able. If a soil is rich in nitrogen and lime, summer 

 fallowing 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 nitrogen is greatly decreased. I7 



Soil before Soil after 



fallowing. fallowing. 



Total nitrogen 0.154 0.142 



Soluble nitrogen 0.002 0.004 



The gain of 0.002 per cent, of soluble nitrogen was 

 accompanied by a loss of 0.012 per cent, of total 

 nitrogen. For every pound of available nitrogen 

 there was a loss of 6 pounds. 



