Relative agronomic merit of fused calcium phosphate. I. Phosphate dissolution and transformation in incubation experiment with four Swedish acid soils
1991
Otabbong, E. | Persson, J.
The dissolution of fused calcium phosphate (FP) and transformation of P were monitored in a silt loam, sandy loam, sandy clay and clay soil (pH in water = 5.3 - 5.8) incubated with 0, 108 or 324 mg P, as FP kg(-1) soil dry wt, for 10, 30 or 60 d. Soluble P was fractionated by sequential extraction using a chloride anion exchanger (P-resin) and solutions of NaHCO3 (PtCO3), NaOH (PtOH) and HCl (P-HCl). Inorganic P (PiCO3, PiOH) and organic P (PoCO3, PoOH) were also determined. The FP treatments significantly (P = 5%) increased both P-resin and P-HCl levels. Over time, the differences between P-resin or P-HCl levels and the controls declined, except in the silt loam soil in which P-resin levels nearly doubled. PtCO3 and PtOH levels did not markedly respond to FP applications. As incubation proceeded PtOH levels significantly (P = 5%) increased both as PiOH and PoOH. This PtOH buildup was accompanied by small declines in PtCO3 levels, with the declines being greater in the PoCO3 than in PiCO3 fraction. P-resin, PiOH and PoOH levels were negatively correlated with those of P-HCl (P = 5%, n = 36). P-resin levels were also negatively correlated with those of PoCO3. Of the small and large FP doses, 12-45% and 51-56%, respectively, had yet to react by the end of the experiment.
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