NITROGEN COMPOUNDS OF THE SOIL 1 17 



others the organic matter contains i part of nitrogen 

 to 18 parts of carbon. In a soil where there exists a 

 wide ratio between the nitrogen and carbon, it is 

 believed that the conditions for supplying crops with 

 available nitrogen are unfavorable. 



130. Losses of Nitrogen from Soils. — When a soil 

 rich in nitrogen is cultivated for a number of years 

 exclusively to grain crops there is a loss of nitrogen 

 exceeding the amount removed in the crop, caused by 

 the rapid oxidation of the organic matter of the soil. 

 Experiments have shown that when a soil of average 

 fertility is cultivated continually to grain that for 

 every 25 pounds of nitrogen removed in the crop there 

 is a loss of 146 pounds from the soil due to the 

 destruction of the organic matter. 17 In general, any 

 system of cropping which keeps the soil continually 

 under the plow, results in decreasing the nitrogen. 

 When a soil is rich in nitrogen the greatest losses 

 occur; when poor in nitrogen there is relatively less 

 loss. There is a tendency toward the establishment 

 of an equilibrium as to the nitrogen content of soils. 

 When a soil rich in nitrogen is given arable culture 

 the oxidation of the organic matter and the losses of 

 nitrogen take place rapidly. 



131. Gain of Nitrogen in Soils. — When arable 

 land is permanently covered with vegetation, there is 

 a gain of nitrogen. Pasture land contains more nitro- 

 gen than cultivated land of a similar character ; also 



