COMMERCIAL FERTILIZERS 103 



116. Low-grade nitrogenous fertilizers. There are a number of 

 materials containing either a low percentage of nitrogen or nitro- 

 gen in a form which becomes available very slowly when applied 

 to the soil, as leather meal, wool and hair waste, horn and hoof 

 meal. These are commonly used in making low-grade fertilizers, 

 but their use as a source of plant food is not recommended. 



117. Nitrogen from the air. Through large electric furnaces 

 operated at low cost by water power, it is possible to combine the 

 nitrogen of the air with other substances at sufficiently low cost 

 to be used for fertilizing purposes. There are two such prod- 

 ucts on the market calcium cyanimide and calcium nitrate. The 

 former contains about 20 per cent of nitrogen, which must be 

 transformed into a nitrate by soil bacteria before it is available. 

 The latter contains about 12 per cent of nitrogen in a readily 

 available form. 



118. Where nitrogenous fertilizers are used. The use of 

 nitrogenous fertilizers is confined largely to regions where heavy 

 fertilization of the soil is practiced. In general, the more soluble 

 forms should be applied at such times and in such quantities 

 as to be of immediate use to the plants, as otherwise they will 

 leach from the soil and be lost. On the other hand, those forms 

 coming from animal and plant products are more slowly avail- 

 able, since the nitrogen must be acted upon by bacteria in the 

 soils ; hence these forms may be used with less danger of the 

 nitrogen being lost by leaching. 



119. Phosphatic fertilizers. Phosphatic fertilizers are obtained 

 from two main sources, animal and mineral. Among the animal 

 phosphates are the bone meals, waste products of the slaughter- 

 houses, and fish scrap. The important mineral phosphates are 

 rock phosphate, basic slag, and acid phosphate. 



Phosphorus l from mineral sources is but slightly soluble in 

 water. When treated with an acid like sulphuric acid, however, 



1 In the publications on fertilizers, phosphorus is expressed in terms of 

 so-called phosphoric acid. In this text it is given as phosphorus, in accord- 

 ance with the best usage. To convert values for phosphorus into values for 

 phosphoric acid, multiply by 2.29. To convert phosphoric acid values into 

 phosphorus values multiply by .43. 



