82 Effective Farming 



will not maintain the productivity of the soil ; some method 

 must be followed of supplying organic matter together with 

 the fertilizer. Barnyard manure and green-manure are excel- 

 lent for this purpose. The fertilizer is easy to haul from the 

 station and the labor of applying it is small. 



35. Nitrogenous fertilizers. Nitrogen is the most ex- 

 pensive plant-food to purchase. In normal times it costs 

 about twenty cents a pound. During war times it, in common 

 with other fertilizer elements, increased much in price. It is 

 supplied from mineral, animal, and vegetable sources and also 

 by the artificial fixation of atmospheric nitrogen. 



Nitrate of soda. The principal mineral used to supply 

 nitrogen is a salt known as nitrate of soda, which is obtained 

 in a crude state in the northern part of Chile. It is purified 

 and when put on the market is about 96 to 97 per cent pure 

 and contains from 15 to 16 per cent nitrogen. It is readily 

 soluble and, for this reason, the nitrogen is quickly available 

 as plant-food. Because of the solubility of the salt, the nitro- 

 gen is easily lost in drainage water; therefore, the fertilizer 

 should usually be applied to the growing crop rather than to 

 the soil before the crop is planted. Small and frequent appli- 

 cations are preferable. For example, three applications of 

 fifty pounds to the acre, say a week apart, is better practice 

 than one of one hundred fifty pounds. Nitrate of soda is 

 used to force the growth of crops, especially vegetables, and 

 is used to some extent in mixed fertilizers. A light application 

 spread on a hay field when the plants are making their first 

 growth in the spring has been found profitable in some instances. 



Sulfate of ammonia. Another mineral substance contain- 

 ing available nitrogen is sulfate of ammonia. It is a by-prod- 

 uct of the manufacture of coal gas, is about 95 per cent pure, 

 and contains about 20 per cent nitrogen. As it contains a 

 larger percentage of nitrogen, it is somewhat more economical 

 to handle than nitrate of soda. It does not, however, become 

 available so quickly, but it is less readily lost by percolation 



