NITROGENOUS MANURES 1 35 



plowed under while green, the practice is called green 

 manuring. This does not enrich the land with any 

 mineral material but results in changing to humate 

 forms inert plant food. Green manuring should take 

 the place of bare fallow, as its effects are in many 

 respects more beneficial. With green manuring, 

 nitrogen is added to the soil while with bare fallow 

 there is a loss of nitrogen. Leguminous crops, as 

 clover, peas, crimson clover, and cow peas, should be 

 made to serve as the main source of the nitrogen for 

 crop production. 



160. Sodium Nitrate. — The nitric nitrogen most 

 frequently met with in commercial forms is sodium 

 nitrate, commonly known as Chili saltpeter. It is a 

 natural deposit found extensively in Chili, Peru, and 

 the United States of Colombia. Various theories have 

 been proposed to account for these deposits, but it is 

 difficult to determine just how they have been formed. 10 

 Their value to agriculture may be estimated from the 

 fact that there are annually used in the United States 

 about 100,000 tons, and in Europe about 700,000 tons. 

 The commercial value of nitrogen in fertilizers is reg- 

 ulated by the price of sodium nitrate which, when pure, 

 contains 16.49 P er cen t. of nitrogen. Commercial 

 sodium nitrate is from 95 to 97 per cent. pure. 

 An ordinary sample contains about 16 per cent, 

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

 the nitrogen worth from 15 to 18 cents per pound. 



