Bones, bone meal and other bone products are the earliest phosphatic materials used as fertilizers. Bone meal is produced and marketed in many forms: raw, steamed, untreated, and crushed. Raw bone meal is prepared by grinding raw bones. It contains 20 to 28% phosphorus pentoxide (7 to 12% P) and 4 to 6% nitrogen. The powder is effective as manure only if the particles are smaller than 2.5 mm.
Raw bones have fatty substances stuck to them, which slow down the decomposition of the bone meal. When bones are treated with steam to remove the fat before grinding, the resultant bone meal is called steamed bone meal or bone flour meal which contains only 2% nitrogen as against 4 to 6% in untreated bones. Steaming makes the bones friable and amenable to fine grinding for soil applications and increases the citrate-soluble phosphorus content.
Bone meal contains 20 to 28% water-insoluble phosphorus (as P2O5), and about 50% citrate-soluble phosphorus (asP2O5). Similar to superphosphate, bone meal is effective in acidic soils for wheat and rice. Burning bones gives bone ash which contains 30 to 40% readily available phosphorus. Bone phosphate of lime (BPL) in a phosphate ore is the content of tri-calcium phosphate, Ca3(PO4)2. In commercial trading, the phosphorus content of phosphate rock is calculated as the weight percentage of tri-calcium phosphate and is expressed as bone phosphate of lime or the total phosphate of lime (TPL).
For phosphate rock to be acceptable commercially as a substance with sufficiently high percentage of phosphorus, it must contain 30 to 40% phosphorus (as P2O5) and 66 to 87 % BPL.
When ground bones are treated with sulphuric acid, bone superphosphate is formed. It contains 1 to 2% nitrogen and 16 % phosphorus (as P2O5). Bone tankage is a concentrated organic manure with animal carcasses, containing 7 to 20% phosphorus (as P2O5) and 3 to 10% nitrogen.
