136 SOILS AND FERTILIZERS 



Sodium nitrate is the most active of all the nitrogenous 

 manures. It is soluble and does not have to undergo 

 the nitrification process before being utilized by crops. 

 On account of its extreme solubility it should be ap- 

 plied sparingly, for it cannot be retained in the soil. 

 As a top dressing on grass, it will respond by impart- 

 ing- a rich green color. It may be used at the rate of 

 250 pounds per acre, but a much lighter application 

 will generally be found more economical. Sodium 

 nitrate may contain traces of sodium perchlorate, 

 which is destructive to vegetation, if the fertilizer is 

 used in excess. 51 Sodium nitrate, in small amounts, 

 is the fertilizer most frequently resorted to when the 

 forcing of crops is desired as in early market garden- 

 ing. Its use for fertilizing horticultural crops has be- 

 come equally as extensive as for general farm crops. 

 Excessive amounts of sodium nitrate may produce in- 

 jurious results. It stimulates a rank growth of dark 

 green foliage, and retards the maturity of plants, but 

 when properly used it is one of the most valuable of 

 the nitrogenous fertilizers. 



161. Ammonium Salts. — Ammonium sulphate is 

 obtained as a by-product in the manufacture of illumi- 

 nating gas and is extensively sold as a fertilizer. It 

 usually contains about 20 per cent, of nitrogen, equiv- 

 alent to 95 per cent, of ammonium sulphate, the re- 

 maining 5 per cent, being moisture and impurities. 

 Ammonium sulphate is not generally considered the 



