Nitrous oxide emission from a sandy loam Inceptisol under irrigated wheat in India as influenced by different nitrification inhibitors

Neem (Azadirachta indica Juss.) is grown widely in India and its products are known to have inhibitory effects on nitrification. Their effects on the emission of N2O from soil have not been explored, however. The role of some neem products and some known nitrification inhibitors on N2O emission from an irrigated wheat (Triticum aestivum L.) crop, var. UP 2338, was evaluated under field (Typic Ustochrept; Inceptisol, sandy loam soil) conditions. The crop was fertilised with urea and urea in combination with four nitrification inhibitors: (1) neem (crushed neem seed powder) coated urea; (2) nimin (commercial derivative of neem) coated urea; (3) dicyandiamide (DCD); and (4) thiosulphate. Nitrous oxide emission was monitored by closed chamber technique for 95 days, at the research farm of Indian Agricultural Research Institute, New Delhi, India. The N2O flux ranged from 0.00056 to 17.35 mg N m(-2) per day during 95 days, with a considerable temporal variability (average CV = 124-182%). The N2O-N flux was the highest from urea-fertilised soil while addition of the nitrification inhibitors lowered the mean N2O-N flux considerably compared to soil fertilised with urea alone. Appreciable increase in N2O-N flux was observed after irrigation and rainfall. Total N2O-N emissions during 95 days were 0.75, 1.43, 1.09, 1.00, 1.36 and 1.19 kg N per ha from control (no nitrogen), urea, urea + DCD, nimin coated urea, neem coated urea and urea + thiosulphate, respectively. Nimin coated urea, urea + DCD, urea + thiosulphate and neem coated urea reduced total N2O-N emission by 63, 49, 35 and 9%, respectively, as compared to urea treatment. Total nitrogen lost from soil as N2O-N was 0.20-0.56% of the applied N. Nimin coated urea inhibited nitrification the most, followed by urea + DCD, urea + thiosulphate and neem coated urea. The promising performance of the inhibitors, especially nimin coated urea underlined the need for further studies on the use of these nitrification inhibitors in N2O emission studies from other crops, fertilised with different nitrogenous fertilisers under different land management practices. (C) 2002 Elsevier Science B.V. All rights reserved.