120 SOILS AND FERTILIZERS 



can be retained in the soil. The crop utilizes only a 

 part of the nitrogen rendered available, the rest being 

 lost by drainage, ammonincation, and denitrification. 

 Hence the available nitrogen is increased while the 

 total nitrogen is greatly decreased. 17 



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 six pounds. Bare fallowing of 

 land should not be practiced, except occasionally to 

 destroy weeds or insects, as it results in permanent 

 injury to the soil. 



151. Influence of Plowing upon Nitrification. 

 In a rich prairie soil nitrification goes on very rapidly. 

 This is one reason why shallow plowing on new 

 breaking gives better results than deep plowing. 

 Deep plowing at first, causes nitrification to take place 

 to such an extent that the crop is overstimulated in 

 growth, due to an excess of available nitrogen. Deep 

 plowing and thorough cultivation aid nitrification. 

 The longer a soil has been cultivated, the deeper and 

 more thorough must be the cultivation. 



Early fall plowing leaves more available nitrogen 

 at the disposal of the crop than late fall plowing. 

 Nitrification takes place only near the surface. Hence 

 when late spring plowing is practiced there is brought 

 to the surface raw nitrogen, while the available nitro- 



