104 AGRICULTURAL BACTERIOLOGY 



the soil is none too large, it is essential that the farmer 

 use every means to conserve the nitrogen supply of the 

 soil. Much can be done in this regard by keeping a crop 

 on the land constantly. For example, after the removal 

 of corn the land may be planted to rye, which will use up 

 the nitrates in the soil. If this crop is plowed under in the 

 spring, the organic matter will decompose, and the nitro- 

 gen be made available for the coming crop. It has been 

 determined that four times as much nitrogen is lost in the 

 drainage water as is removed in the crop. This loss is par- 

 ticularly heavy in the South, where the long exposure of 

 the soil to the winter rains gives a most favorable oppor- 

 tunity for leaching. 



The fallow method of handling the soil results in the es- 

 tablishment of favorable conditions for decomposition, be- 

 cause of the well aerated condition of the soil and the re- 

 tention of moisture in the summer months. Plant food 

 thus accumulates in the form of nitrates, so that when a 

 crop of winter wheat or rye is sown in the fall, rapid 

 growth occurs. 



Nitrate deposits. Almost all of the nitrate used in the 

 industries and as a fertilizer is obtained from natural de- 

 posits in Chile. It is believed that the deposits are due to 

 the accumulation of large amounts of organic matter in 

 some arm of the sea. This was raised above sea-level, and 

 underwent decomposition in a region in which the rainfall 

 was not sufficient to leach the nitrate into the deeper levels 

 of the soil, so it accumulated in some such manner as it 

 is now accumulating in some parts of the West. In sections 

 of Colorado the nitrate content of orchards and of fields 

 has become so high as to destroy all vegetation. 



Denitrification. Nitrogen is removed from the reach of 

 green plants by both chemical and biological processes, 

 For example, in the discharge of explosives of all kinds, 



