92 Practical Farming 



Sources of explained later, it must be returned to the 

 Phosphorus g^jj -j^ ^^^ manure, or fertilizers applied. 

 In some cases where farmers find it profitable to feed 

 on the farm food raised elsewhere it may be possible 

 to keep up the supply of phosphorus in the soil with- 

 out the purchase of phosphates. And right here we are 

 reminded that in many parts of the country the farmers 

 have got into the habit of calling all commercial fertilizers 

 phosphates. Of course, all complete fertilizer mixtures 

 have some phosphate or generally phosphoric acid in 

 them, but the term phosphate is applicable only to the 

 dissolved phosphatic rock known as acid phosphate. 

 The complete mixtures are always called commercial 

 fertilizers. Formerly, almost the entire supply of phos- 

 phorus came from the bones of animals. When these 

 bones are ground raw they will usually contain from 20 

 to 28 per cent, of phosphoric acid and about 4 per cent, 

 of nitrogen. Since the phosphoric acid is in an insoluble 

 form its becoming available depends largely on the fine- 

 ness of the material, and if the bones are fresh it is hard to 

 get them very fine on account of the oily matter associated 

 with them. To rid fresh bones of this oily matter they are 

 often steamed. This steaming also takes out most of the 

 nitrogen. Accordingly the steamed bone is valuable only 

 for its phosphoric acid, though at times a small percentage 

 of nitrogen may remain. But as a source of phosphoric 

 acid the steamed bone is better than the raw. 



Tankage, which we have referred to as a source of nitro- 

 gen, also contains bone and furnishes a considerable 

 amount of phosphoric acid in variable amounts depending 

 on the character of the material used. 



