Reducing nitrous oxide emission from an irrigated rice field of North India with nitrification inhibitors

Nitrification inhibitors may be potential management strategy to reduce N2O emissions in irrigated rice (Oryza sativa L.). A field experiment was conducted to evaluate chemically synthesized as well as locally available neem plant products on N2O emissions, from an irrigated rice at New Delhi, India. Emission of nitrous oxide (N2O) was monitored during 70 days by closed chamber method in rice (var. IR-72) grown on a Typic Ustochrept (cambisol) soil. Treatments were control (no nitrogen), urea alone, urea mixed with different nitrification inhibitors, namely, urea plus dicyandiamide (DCD), neem (powdered Azadirachta indica Juss. seeds) coated urea and nimin (commercial derivative of neem) coated urea. Total N2O-N emission was highest with urea (59.9 g N2O-N ha(-1)) and lowest in the control (34.3 g N2O-N ha(-1)). Total N2O emission from both nimin coated urea and neem coated urea were not significantly different from urea alone. Urea treated with DCD significantly reduced N2O emissions from urea alone (48.9 g N2O-N ha(-1)). Nitrogen lost through N2O emission were 0.018, 0.010, 0.016 and 0.013% of total nitrogen applied through urea, urea plus DCD, nimin coated urea and neem coated urea, respectively. Fluxes of N2O were low during flooding but increased markedly during drainage of standing water. After 70 days of transplanting of rice, N2O flux was hardly detectable in any of the treatments. The study indicated that some plant products, such as neem seeds and nimin which are more readily available with farmers in India, might be useful in mitigating N2O emissions from rice in addition to DCD, which is a widely used nitrification inhibitor. (C) 2000 Elsevier Science B.V. All rights reserved.