132 SOILS AND FERTILIZERS 



nitrogen, while in soils from the humid regions there is 

 from 4 to 6 per cent. 45 In some soils the ratio of nitro- 

 gen to carbon is I to 6, while in others it may be I to 

 1 8, or more. That is, in the organic matter of some soils 

 there is i part of nitrogen to 6 parts of carbon, while in 

 others the organic matter contains I part of nitrogen to 

 1 8 parts of carbon. In a soil where there exists a wide 

 ratio between the nitrogen and carbon, it is believed the 

 conditions for supplying crops with available nitrogen 

 are unfavorable. 



144. Losses of Nitrogen from Soils. When a soil 

 rich in nitrogen is cultivated for a number of years ex- 

 clusively to grain, there is a loss of nitrogen exceeding 

 that removed in the crop, caused by the rapid oxida- 

 tion of the organic matter of the soil. Experiments 

 show that when a prairie soil of average fertility is 

 cultivated continually to grain, for every 25 pounds of 

 nitrogen removed in the crop there is a loss of about 

 1 50 pounds due to the destruction of the organic mat- 

 ter. 18 In general, any system of cropping which keeps 

 the soil continually under the plow results in decreas- 

 ing the nitrogen. When a soil is rich in nitrogen the 

 greatest losses occur; when poor in nitrogen there is 

 relatively less loss. When a soil rich in nitrogen is 

 given arable culture, oxidation of the organic matter and 

 losses of nitrogen take place rapidly. The longer a 

 soil is cultivated, the slower the oxidation of the humus 

 and relative loss of nitrogen. 



