CHAPTER XIII 

 NITROGEN 



89. Importance of Nitrogen. The need of nitrogen in 

 crop production cannot be over-emphasized. The lack of 

 a plentiful supply of this element in the organic form will 

 inevitably make land infertile. In the formation of the 

 earth's crust, the addition of nitrogen must have been 

 very gradual, the first probably being due to the oxidation 

 of atmospheric nitrogen by electrical disturbances. This 

 operation is still effective, and oxides of nitrogen and 

 ammonia gas (NHs) in small amounts are washed down 

 by rain water. Nitrogen from this source must have 

 nourished the earliest forms of plant life, and the organic 

 remains of these lower plant forms must have supplied the 

 basis for our supply of organic nitrogen in the soil. Neces- 

 sarily the accumulation of this supply required very long 

 periods of time. 



When enough organic matter had accumulated to make 

 possible the growth of legumes, the accumulation of nitro- 

 gen probably became much more rapid, as these plants 

 bear round their roots nodules which are the homes of 

 colonies of a species of bacterium that have the power of 

 causing the nitrogen and oxygen of the air to unite, thereby 

 " fixing " the nitrogen. There are to-day many wild 

 legumes still adding to the supply of nitrogen in an organic 

 form. Therefore, the cultivation of domestic legumes, such 

 as the clovers, cowpeas, vetches, alfalfa, field peas, beans, 

 lupines, and peanuts cannot be urged too strongly. Certain 

 sections of the United States make successful use of these 

 crops in rotation, to furnish their nitrogen supply. For 

 specialized crops, such as cotton, tobacco, sugar cane, 



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