Phosphorus and Sulphur Availability in Soil Following Incorporation of Various Organic Residues

A study was conducted under controlled conditions in laboratory to develop models for prediction equatilJns of phosphorus (P) and sulphur (8) availability in soil due to incorporation of organic residues varying in content of these nutrients. The residues were sorghum (Sorghum bicolor (L.) Monech), mungbean (Vigna radiata), Leucaena leucocephala, perennial pigeonpea (Cajanus cajan), groundnut shell (Arachis hypogaea) and FYM These materials were added in quantities equivalent to 40 kg N ha⁻¹, thereby the amount of residue applied rangedfrom 1.21 t ha⁻¹ to 8.00 t ha⁻¹. Soil water was maintained at 0.5 field capacity (FC) and field capacity (FC) to simulate rainfed and irrigated conditions, respectively. Prediction models with high level of significance were developed for P availability in soil that varied with the type of residue incorporated. From these models, the amount of P that is likely to be extractable can be computed on a given day, up to 120 days as done in this investigation. At 0.5 FC, incorporation of loppings of perennial pigeonpea, sorghum stover and FYM caused initial immobilization of P which levelled of f at about 21 to 31 days of incubation. No P immobilization was observed with other residues at 0.5 Fe. At FC, none of the residues caused immobilization. The quantity of P released was significantly related to the amount of P added through residues. Sulphur availability in soil increased up to 60 days and decreased thereafter.