Phosphorus fractions in soil fertilised with organic waste

The aim of this study has been to evaluate the effect of sewage sludge and composted sewage sludge and municipal waste on the content of various forms of P in soil. The experiment scheme: C, control; NPK; FYM; DGSS, dried and granulated sewage sludge; CSS, composed sewage sludge; CSSS, composted sewage sludge and straw; CMMW, composted mixed municipal waste; CMGW, composted municipal green waste. The content of bound P was determined in the fractions: F1, easily soluble; F2, exchangeable; F3, organic; F4, carbonate; F5, stable organic-mineral and mineral bonds; and F6, residual. The NPK fertilisation as well as the soil fertilisation with organic substances raised the P-total content and of P bound in the fractions: F3, F4, F5 and F6. The highest amount of phosphorus in the studied soil was in fraction F3 (phosphorus in organic compounds) and the lowest in fraction F1 (phosphorus in the ionic form as H2PO4− and HPO42−). Composted sludge and straw introduced into the soil increased the content of readily soluble P (F1), while the NPK effect was reversed. NPK fertilisation and enhancement of soil organic matter (except CSSS, CMGW) led to a reduction of the P content in F2 fraction. The content of available P determined by the Egner-Riehm method depended on the content of C-organic, P-total and CEC soil. Among the determined phosphorus fractions, the content of available P was most strongly correlated with the content of P bound in the carbonate fraction (F4) and residual fraction (F6) and, less strongly, with the organic phosphorus fraction.