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 N 2O from soil have not been explored, however. The role of some neem products and some known nitrification inhibitors on N 2O 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 N 2O 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 N 2O–N flux was the highest from urea-fertilised soil while addition of the nitrification inhibitors lowered the mean N 2O–N flux considerably compared to soil fertilised with urea alone. Appreciable increase in N 2O–N flux was observed after irrigation and rainfall. Total N 2O–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 N 2O–N emission by 63, 49, 35 and 9%, respectively, as compared to urea treatment. Total nitrogen lost from soil as N 2O–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 N 2O emission studies from other crops, fertilised with different nitrogenous fertilisers under different land management practices.