Availability and fractionation of inorganic phosphorus in a sewage sludge-amended calcareous soil

Information of P fractions in sewage sludge treated soils is necessary for better management of land application of organic amendments. The purpose of this study was to evaluate the effect of sewage sludge on the forms and distribution of P in a calcareous soil using a sequential fractionation procedure. A greenhouse experiment with six levels of sewage sludge (0, 22.5, 45, 90, 180 and 360 ton ha-1) was conducted as a completely randomized design with four replications with wheat plant for 90 days. In comparison with the control, sewage sludge application significantly increased all P forms. Among various P fractions, labile P showed the largest increase. In the control soil, the various P fractions could be ranked in the following order: HCl-P> OAc-P> CBD-P> NaCl-NaOH-P> Labile-P. In contrast, the order in biosolid-treated soils follows: HCl-P> OAc-P> Labile-P> CBD-P> NaCl-NaOH-P. In general, the results demonstrated that the dominance of inorganic P forms in sewage sludge. Inorganic P forms represented 80% of total P in biosolid-treated soils and 57% in the control. In control soil and biosolid-treated soils, Ca-associated Pi was the dominant fraction. Application of sewage sludge significantly increased the concentration of P in shoots of wheat compared with the non-manured control.