Evaluation of alkaline phosphatase activity and availability of various P fractions for bean (Phaseolus vulgaris) in some calcareous soils amended with municipal sewage sludge

To evaluate the relationship of various P fractions and alkaline phosphatase activity with bean indices growing in 10 calcareous soils، amended with municipal sewage sludge from Chaharmahal-Va-Bakhtiari province، a greenhouse research was carried out. Soil samples were incubated for one month with sludge at a rate equivalent to 1% (w/w). Then، the P fractions، including P adsorbed by Fe and Al oxides (]NaOH+CB]-P)، occluded P (CBD-P) and P absorbed by Ca (HCl-P)، were determined by Olsen and Summers'' sequential fractionation procedure. Furthermore، total P، organic P and residual P were determined. Also، alkaline phosphatase activity was measured. A pot experiment in a completely randomized design with three replications in the ten soils was done to evaluate the bean plant indices. The results showed that the amount of P fractions decreased in the following order: HCl-P>residual-P>]NaOH+CB]-P > OP>CBD-P. The results also indicated that alkaline phosphatase activity was significantly correlated with CBD-P fraction، organic P and total P. In addition، significant correlations were found between ([NaOH+CB] -P) and HCl-P and plant shoots. In general، the results of this research showed that P fractionation method appears to be a powerful tool to identify the P status and availability in the soils amended with sewage sludge.