NITROGEN, NITRIFICATION, NITROGENOUS MANURES 155 



nitrogen and costs from $50 to $60 per ton, making 

 the nitrogen worth from 15 to 18 cents per pound. 

 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 

 should not be used when heavy dressings of farm 

 manure are applied, as denitrification may result from 

 such a practice. In small amounts it is the fertilizer 

 most frequently resorted to when the forcing of crops 

 is desired, as in early market gardening. Its use for 

 fertilizing horticultural crops has become equally as ex- 

 tensive as for general farm crops. Excessive amounts, 

 however, may produce injurious results. Sodium nitrate 

 stimulates a rank growth of dark green foliage and 

 retards the maturity of plants, but when properly used 

 is one of the most valuable of the nitrogenous ferti- 

 lizers. 



174. Ammonium Sulphate. Ammonium sulphate is 

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

 minating 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- 



