NITROGEN COMPOUNDS OF THE SOIL III 



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 un- 

 favorable. 



133. 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, for every 

 25 pounds of nitrogen removed in the crop there 

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

 struction of the organic matter. 18 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. When a soil rich in nitrogen is given arable 

 culture the oxidation of the organic matter and the 

 losses of nitrogen take place rapidly. The longer a 

 soil is cultivated, the slower the oxidation of the 

 humus and the relative loss of nitrogen. 



134. 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 

 in meadow land, there is a tendency for the nitrogen 

 to increase. These facts are well illustrated in the 

 investigations of Lawes and Gilbert, at Rothamsted. 44 



