102 .THE ESSENTIALS. OF AGRICULTURE 



use of commercial fertilizers has been confined largely to the 

 Eastern and Southern states, but as the land of the corn belt 

 becomes more worn, increasing amounts of commercial fertilizer 

 are being used. 



111. Nitrogenous fertilizers. Fertilizing material containing 

 nitrogen may be divided into two general classes, animal prod- 

 ucts and plant products. Among the common animal products 

 are wastes from the slaughterhouses, such as dried blood and 

 tankage. With these may be classed the guanos, made up of 

 the excrement of sea fowls, gathered from islands of the west 

 coast of Africa. The common materials derived from the plant 

 world are cotton seed and cotton-seed meal, linseed meal, and 

 castor pomace. Other products, as sodium nitrate and ammonium 

 sulphate, are quite largely used. 



112. Nitrate of soda. The most widely known nitrogenous 

 fertilizer is nitrate of soda, which is found in the rainless region 

 of Chile. As it comes on the market it contains about 16 per 

 cent of nitrogen. It is entirely soluble in water and therefore is 

 immediately available for plant use. It should be applied only 

 where plants can make immediate use of it ; otherwise it may 

 leach out of the soil and be lost. 



113. Sulphate of ammonia. The principal source of sulphate 

 of ammonia is coal, it being a by-product of the manufacture 

 of gas and coke. It contains about 20 per cent of nitrogen, 

 and is entirely soluble in water. However, the nitrogen must be 

 largely transformed to a nitrate by nitrifying bacteria before it 

 can be used by plants. 



114. Dried blood. One of the most important sources of ani- 

 mal nitrogen is dried blood. The nitrogen it contains must be 

 transformed to a nitrate by bacteria before it is available to plants. 

 Red blood contains from 13 to 14 per cent of nitrogen, and 

 black blood from 6 to 12 per cent. 



115. Tankage. This is a term applied to various miscellane- 

 ous waste materials of the slaughterhouses which are dried 

 and ground. It contains from 4 to 1 2 per cent of nitrogen and 

 from i to 5 per cent of phosphorus. 



