Relative Mineralization of Nitrogen and Phosphorus from Farm Yard Manure, Biogas Slurry and Sewage Sludge

An incnbation study was carried out in plastic containers with FYM, biogas slurry and sewage sludge added in sandy clay loam soil @ 5, 10 and 15 t ha⁻¹ with and without N–P fertilizer. Moisture was maintained at field capacity level throughout the incubation period and samples were drawn at the 1, 2, 4, 8 and 16 weeks and analysed for NH₄-N, NO₃+NO₂-N, saloid-P, AI-P, Fe-P and Ca-P. Ammonium-N decreased and NO₃+NO₂-N increased significantly with increase in incubation period from 1 to 16 weeks in all the organic manures. Highest NH₄-N was observed in sewage sludge followed by biogas slurry and FYM. Higher rate (15 t ha⁻¹) of all the manures mineralized significantly more NH₄⁺ and NO₃+NO₂-N fractions. Addition of urea and single superphosphate at 120 kg N and 60 kg P₂O₂ ha⁻¹ enhanced the mineralized both the NH₄-N and NO₃+NO₂-N contents. Among the inorganic phosphorus fractions, saloid-P decreased while Al-P, Fe-P and Ca-P increased significantly with increasing period of incubation. However, magnitude was more in sludge followed by biogas slurry and FYM. Based on their mineralization behaviour, the relative effectiveness of organic manures was observed in the order: Sewage sludge > Biogas slurry > FYM.