112 SOILS AND FERTILIZERS 



Age of Pasture Nitrogen 



Years. Per Cent. 



Arable land o. 14 



Barn-field pasture 8 0.151 



Apple-tree pasture 18 0.174 



Meadow 21 0.204 



Meadow 30 0.241 



After deducting the amount of nitrogen in the manure 

 added to the meadow land, the annual gain of nitrogen 

 was more than 44 pounds per acre. 



Another source of gain of nitrogen is the fixation of 

 the free nitrogen of the air by the growth of clover 

 and other leguminous crops. If a soil is properly 

 manured and cropped the amount of nitrogen may be 

 increased. A rotation of wheat, clover, wheat, oats, and 

 corn with manure will leave the soil at the end of the 

 period of rotation in better condition as regards nitro- 

 gen than at the beginning. These facts are illustrated 

 in the following table : l8 



CONTINUOUS WHEAT CULTURE 



Nitrogen in soil at beginning of experiment 0.221 per cent. 



Nitrogen at end of 5 years continuous wheat culti- 

 vation 0.193 " " 



Loss per annum per acre (in crop 24.5, soil 146.5). 171 pounds. 



ROTATION OF CROPS 



Nitrogen in soil at beginning of rotation 0.221 per cent. 



Nitrogen at close of rotation 0.231 ' 



Gain to soil per annum per acre 61 pounds. 



Nitrogen removed in crops per annum 44 



It is to be regretted that in the cultivation of large 

 areas of land to staple crops as wheat, corn, and cotton, 

 the methods of cultivation followed are such as to de- 

 crease the nitrogen content and crop producing power 

 of the soil when this could be prevented. 



