498 SOILS: PROPERTIES AND MANAGEMENT 



inorganic forms of nitrogen has not been definitely worked 

 out. Certain organic nitrogenous fertilizers — as, for ex- 

 ample, dried blood — have a high commercial value, the 

 nitrogen in this form selling for more a pound than the nitro- 

 gen in any of the inorganic salts. Many crops, especially 

 among garden vegetables, are most successfully grown only 

 when supplied with organic nitrogenous material. Some 

 nitrate nitrogen is always present under natural soil con- 

 ditions, so that crops are never limited to organic nitro- 

 gen alone ; and it may be that the latter form of nitrogen 

 is most useful when it supplements the nitrate nitrogen. 



420. Sodium nitrate. — This now constitutes the prin- 

 cipal source of inorganic nitrogen in commercial fertilizers. 

 The salt exists in the crude condition in northern Chili. 

 The crude salt is purified by crystallization, and as put 

 on the market it contains about 96 per cent sodium 

 nitrate, or about 16 per cent of nitrogen, 2 per cent of 

 water, and small amounts of chlorides, sulfates, and in- 

 soluble matter. The cost of nitrogen in this form is 

 from fifteen to eighteen cents a pound. 



Because of its easy availability, sodium nitrate acts 

 quickly in inducing growth. For this reason it is used 

 much by market gardeners, and for other purposes when 

 a rapid growth is desired. It is the most active form of 

 nitrogen. A light dressing on meadowland in early 

 spring assists greatly in hastening growth by furnishing 

 available nitrogen before the conditions are favorable 

 for the process of nitrification. On small grain a similarly 

 useful purpose is served where the soil is not rich, 

 y Owing to the fact that nitrate is not absorbed by the 

 soil in large quantities, it is easily lost in the drainage 

 water ; for this reason it should be applied only when crops 

 are growing on the soil, and then only in moderate quantity. 



