CHAPTER IX 

 NITROGENOUS FERTILIZERS 



Of the various plant foods which the farmer must buy, 

 those containing nitrogen are the most expensive. Nitrogen 

 has usually been considered the most important element in 

 plant nutrition, and for several reasons: It exists in the 

 soil in only small quantities, rarely more than 0.2 per cent. 

 It is so important in the vegetative growth of plants that 

 frequently nitrogen is the only fertilizing constituent needed 

 to produce large yields. In other words, the increased 

 growth of leaves and stems gives the plant more power to 

 forage for the other elements in the soil and so produce a 

 greater yield. It goes for the most part to the seed, and thus, 

 in the case of grain crops, is one of the elements that is 

 removed from the soil. It is used by plants to a greater 

 extent than any other element. Finally, as mentioned above, 

 it is the most expensive, although possibly the latter fact 

 is a result, not a cause, of its importance. 



As a matter of physiological fact, of course, no one element 

 is more important than another. All the essential elements 

 are equally necessary for the growth of the plant; some in 

 larger amounts than others, it is true, but not more necessary. 

 And yet, important as nitrogen is in many ways, it is the 

 only element which can be returned to the soil bv natural 

 means, namely, by the agency of nitrogen-fixing bacteria on 

 the roots of legumes (Section 130). Clover, alfalfa, or some 

 other legume, is always a part of a good rotation system. 

 So that after all, nitrogen, except for its high cost, is not the 

 important element for the farmer to consider. 



In taking up the different forms of nitrogen on the market 

 it is convenient to classify them according to the form of 

 chemical combination, and this order coincides with the 

 solubility, and roughly with the availability of the nitrogen 

 compounds. 



