CHAPTER XII 

 PHOSPHORIC ACID FERTILIZERS 



Fertilizers commonly used in this country for their phos- 

 phoric acid may be divided into two classes, natural phos- 

 phate fertilizers and acid phosphate fertilizers. The former 

 are in the condition in which they are found in nature, and 

 are very difficultly soluble. The latter are merely the phos- 

 phate fertilizers that have been treated with strong acid, 

 after which process they are readily available to plants. 

 There is an intermediate form present in basic slag, which is 

 not quite so available as the acid phosphate, but more 

 readily available than the natural phosphate fertilizers. 

 Natural phosphates, when in organic compounds, like bone, 

 are more readily available than when in purely inorganic 

 compounds, like rock. 



220. Bone phosphate. — Most of the bone now used in 

 fertilizers has been steamed or boiled, which removes the fat, 

 and also the nitrogen that fresh bones contain. Fresh bones 

 have a content of about 22 percent phosphoric acid and 

 4 percent nitrogen. . Steamed bones have from 28 to 30 per- 

 cent phosphoric acid and 1.5 percent nitrogen. Bone tankage, 

 which has already been spoken of as a nitrogenous fertilizer, 

 contains from 7 to 9 percent of phosphoric acid. Bone should 

 always be finefy ground, as it is then more readily available. 

 It is a slow acting form of phosphoric acid. 



221. Mineral phosphates. — These are found as natural 

 deposits of rock in various parts of the world, some of the 



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