Soil Fertility 83 



to lower levels in drainage water. When used in large quan- 

 tities for several seasons, it has a tendency to make the soil 

 acid; consequently it should not be used on soils that are 

 already acid. Like nitrate of soda, it should usually be ap- 

 plied to the growing crop rather than to the soil before it is 

 plowed. 



Dried blood. An important fertilizer of animal origin is 

 dried blood, a by-product of meat-packing houses. There 

 are two grades on the market ; one is bright red in color and 

 contains about 13 to 15 per cent of nitrogen, the other is almost 

 black and contains about 6 to 12 per cent. Dried blood decays 

 rapidly in the soil and the nitrogen becomes available by the 

 process of nitrification. It should not be distributed directly 

 with the seeds, as it has a tendency to rot them, but should 

 be drilled into the soil before the seeds are sown. 



Tankage. The fertilizer known as tankage is, like dried 

 blood, obtained from the meat-packing houses, and is made up of 

 animal refuse that has no other use. Two grades are offered 

 for sale, the concentrated, which contains about 10 to 12 per 

 cent of nitrogen, and the crushed, which contains from 4 to 9 

 per cent. Tankage is somewhat slower-acting than dried 

 blood and has a tendency to rot the seeds if applied with them. 



Fish-scrap. The refuse from fish canneries is sold for 

 fertilizer. Although it is somewhat variable in quality, it 

 usually contains about 8 per cent of nitrogen. It also con- 

 tains about 6 per cent of phosphorus. 



Hoof-and-horn meals. The refuse meals from factories 

 manufacturing combs and buttons from hoofs and horns are 

 used to some extent as fertilizer. They contain about 12 per 

 cent of nitrogen, but they have the disadvantage of decom- 

 posing very slowly in the soil. For this reason they are not 

 good for immediate crops; they serve only to build up the 

 nitrogen-content of a depleted soil. 



Cottonseed meal. Cottonseed meal is a vegetable product 

 sometimes used as fertilizer, especially in the South. It con- 



