Poorly soluble, iron-aluminium phosphates in ammonium phosphate fertilizers: Their nature and availability to plants

Abstract

Both monoammonium and diammonium phosphate fertilizers contain various (Ca,Mg)(NH4)- (Fe,Al)(PO4)(F,OH)H2O compounds that are insoluble in water and comprise 4.9-9.9% of the total phosphorus content of the fertilizers. The compounds have been isolated and characterized by chemical, X-ray powder diffraction, ix., and thermogravimetric techniques. The compounds are only 35-60% as effective as monocalcium phosphate (MCP) in supplying phosphorus to wheat grown under glasshouse conditions. The residual effectiveness of the compounds for a second crop of wheat was generally lower (10-20% relative to freshly applied MCP) than the residual value of MCP (20 %).