Determination of phosphorus in fertilizers

Another naturally occurring phosphate mineral is sombrerite (whitlock-ite), which is tricalcium phosphate, Ca3(P04)2. 

Thus one formula Ca is converted to dihydrogen phosphate, and the product is called single superphosphate (the super refers to its solubility/availability compared with rock phosphate). 

With phosphoric acid, the main equation becomes  

A common source of organic phosphorus is bone meal (approximately 9-14% P) and bone ash (approximately 18%). The bird excrement guano contains about 2-3% P as ammonium and calcium phosphates. Fresh solid dairy cattle manure has approximately 0.13% P (moisture = 81.7%), and solid swine manure has about 0.33% P (moisture = 71.8%), which will be in both organic and mineral forms. 

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