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

Information on the P fractions in soils treated with sewage sludge is needed to better manage land application of organic amendments to agricultural soils. The purpose of this study was to evaluate the effect of sewage sludge on the forms and distribution of P in a calcareouse treated soil using a sequential fractionation procedure. Thus, a greenhouse experiment with six levels of sewage sludge application (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 non-manured control, sewage sludge application significantly increased the levels of all P forms. Among various P fractions, the largest increase occurred for soil labile P. In the control soil, the various P fractions could be quantitatively 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.