CHAPTER XXI 

 COMMERCIAL FERTILIZERS 



THE RAW MATERIALS 



NEXT to the soil itself, the farmer's most impor- 

 tant sources of plant food are the farm manures. 

 But most farms do not produce these in sufficient 

 quantities to keep up the plant food side of fer- 

 tility. Therefore the farmer must resort to other 

 sources of plant food to supplement the farm ma- 

 nures. 



There is a large class of materials called Com- 

 mercial Fertilizers, which, if judiciously used, will 

 aid in maintaining the fertility of the farm with 

 economy. 



We learned in a previous chapter that the plant 

 foods, nitrogen, phosphoric acid, potash and lime, 

 are apt to be found wanting in sufficient available 

 quantities to supply the needs of profitable crops. 

 We learned also that lime is useful in improving 

 the texture of the soil and in making other plant 

 foods available. Now the commercial fertilizers 

 are used to supply the soil with these four sub- 

 stances and they may be classified according to the 

 substance furnished as follows: 

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