Utilization of Sewage Sludge for Enhancing Agricultural Productivity

A microplot field experiment was conducted to study the effect of irradiated and unirradiated sewage sludge on dry matter yield and N uptake of wheat. Sewage sludge was applied at rates equivalent to 120, 180, and 240 kg N ha -1, either with or without 15N-labelled (NH4)2SO4-N at 20 kg ha-1. In addition, one control (no treatment) and a treatment receiving 120 kg N ha -1 as 15N-labelled (NH4)2SO4 was also included in the experiment. Wheat was grown to maturity and the plots were then sown to Sesbania aculeata (a green manuring legume). A highly positive effect of sewage sludge, whether irradiated or unirradiated on dry matter yield and N uptake. Sewage sludge not only served as an additional source of plant available N but it helped conserve fertilizer N leading to its increased uptake by plants. The beneficial effect of sludge was more pronounced in the presence of fertilizer N and the effect increased with the rate of application. The effects seemed to persist after harvesting wheat as suggested by higher dry matter yield and N yield of Sesbania. However, the analyses of physico-chemical and biological properties of the soil after harvesting wheat indicated that probably the applied sewage sludge decomposed quite rapidly and thus did not add much to the soil organic matter content and other properties. Nevertheless, N content of the soil showed some improvement although not very consistent with the rate of application.