CHAPTER VII 



COMMERCIAL FERTILIZERS 



A commercial fertilizer is a manufactured plant food. It is 

 usually kept for sale at the warehouses and seed stores. 

 Commercial fertilizers are used when the soil is lacking in 

 some of the important plant food elements, or when the 

 farmer wishes to give his plants an extra good start in order 

 to produce larger crops. Gardeners frequently use commer- 

 cial fertilizers in place of stable manure, because the stable 

 manure contains so many weed seeds that it makes land 

 weedy. Fertilizers do not contain any weed seeds. 



There are many kinds of fertilizers, but they nearly all 

 belong to one of three classes, namely, those which furnish 

 nitrogen, phosphoric acid, or potash. Some fertilizers sup- 

 ply more or less of all three of these elements, but usually 

 some one element is largest in amount. When a substance 

 or mixture supplies all three plant food elements it is said to 

 be a complete fertilizer. We can speak of only a few of the 

 more common fertilizing materials. 



The nitrogen fertilizers come from two sources, namely, 

 from plant or animal sources, that is, organic materials, and 

 from chemical sources. 1. Dried blood comes from the large 

 slaughtering houses. The fresh blood from the animals killed 

 is collected and dried. The best grades of dried blood con- 

 tain 12 to 14 per cent, of nitrogen. Dried blood decays rather 



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