134 SOILS AND FERTILIZERS 



After deducting the amount of nitrogen in the ma- 

 nure added to the meadow land, the annual gain of nitro- 

 gen was more than 44 pounds per acre. 



If a soil is properly manured and cropped, the 

 nitrogen may be increased. A five-course rotation of 

 small grains, clover, and corn (manured) will generally 

 leave the soil at the end of the period of rotation in 

 better condition as regards nitrogen than at the be- 

 ginning. 



At the Minnesota Experiment Station where wheat, 

 corn, barley, and oats were grown continuously for 

 twelve years, a loss of about 2000 pounds per acre of 

 nitrogen was sustained ; from f to ^ of the nitrogen be- 

 ing lost in various ways and not utilized as plant food. 85 

 In experiments covering ten-year periods, it was found 

 that the five-year rotations, in which clover formed an 

 essential part, resulted in a slight increase in the nitro- 

 gen content of the soil, about 300 pounds per acre in 

 excess of that removed in the crops. When timothy 

 and non-legumes were substituted for clover, "a loss 

 of nitrogen from the soil occurred, but the carbon 

 (humus) content was maintained ; the loss of nitrogen 

 from the soil only slightly exceeding that removed by 

 the crops." 96 



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 might be prevented. 



