Co-composts of sewage sludge, farm manure and rock phosphate can substitute phosphorus fertilizers in rice-wheat cropping system.

In the present study, various co-composts of sewage sludge (SS), farm manure (FM) and rock phosphate (RP) were prepared and their influence on phosphorus (P) uptake, soil P restoration and growth of rice crop and residual effect on wheat crop were investigated. The treatments comprised of T1 (control, no amendment), T2 (452 kg Nitrophos ha-1, T3 (724 kg SS50:FM50 ha-1), T4 (594 kg SS100:FM0 ha-1), T5 (728 kg SS25:FM25:RP50 ha-1), T6 (726 kg SS5O:FM25:RP25 ha-1), T7 (508 kg SS75:FM0:RP25 ha-1), and T8 (546 kg SS50:FM0:RP50 ha-1). The post-experimental soil samples were analyzed for pH, EC, OM, Olsen's P. The plant samples (grains and straw of both crops) were analyzed for concentrations of P, and heavy metals. The P adsorption by post-wheat composts-amended soil was tested through Langmuir, and Freundlich adsorption isotherms. The investigated parameters (biomass, grain and straw yield, plant height and P concentrations in plant parts) were significantly increased in all composts as compared to the control treatment. The P uptake by the plants was higher in compost treatments as compared to the control and NP that shows long-term residual effect of applied composts. The maximum grain yield (1.63 Mg ha-1) was obtained in T5 followed by T6 (1.52 Mg ha-1). The P concentration in rice grains were recorded in the trend as T8 (2.55%) > T6 (2.24%) > T4 (1.92%) = T3 (1.88%) > T7 (1.62%). It is evident that the combined application of FM (25%) and RP (50%) enhanced the effect of SS (25%) in terms of P bioavailability and yield parameters and can be effectively used as P fertilizer.