Effects of Phosphorus Form on Short-Term Solubility and Availability in Soils

A laboratory experiment was set up to compare solubility and availability of four phosphate fertilizer sources over a period of 32 d after application to soils with varying pH levels. Three soils, one acidic and two alkaline, of which one was noncalcareous and one calcareous, of similar texture and organic matter, were selected. A large number of samples treated with four phosphate products, namely, two ammonium orthophosphate (9–18–9 and 6–24–0), a polyphosphate (10–34–0), and an ammonium monophosphate (11–52–0) at rates of 100 mg phosphorus (P) kg−1 soil, and an unfertilized control were incubated for a period of 32 d. Destructive sampling at 0, 1, 2, 4, 8, 16, and 32 d was used to assess water-soluble and bicarbonate-extractable P. All treatments were replicated four times. Wide differences in soluble and bicarbonate-extractable P levels from all four products in all three soils at the onset of incubation became insignificant after 2 to 4 d of incubation, suggesting that there was no difference in P av...