Effect of phosphorus form on short-term solubility and availability in soils

Abstract

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, one of which was non-calcareous 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 mono phosphate (11-52-0) at a rate of at 100 mg 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 phosphorus (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 when any of these products applied at seeding time would offer any advantage over the rest.