Mitigation of N 2 O and CH 4 emission from rice and wheat cropping systems using dicyandiamide and hydroquinone P. Boeckx 1, *, X. Xu 2 and O. Van Cleemput 1 1 Laboratory of Applied Physical Chemistry – ISOFYS, Faculty of Bioscience Engineering, Ghent University, Coupure 653, 9000 Ghent, Belgium; 2 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; *Author for correspondence (e-mail: pascal.boeckx@ugent.be) Key words: Inhibitor, Methane, Mitigation, Nitrification, Nitrous oxide, Urease Abstract Agriculture contributes considerably to the emission of greenhouse gases, such as N 2 O and CH 4 . Here we summarize results from previous pot experiments assessing the effectiveness of urease and nitrification inhibitors reducing both N 2 O and CH 4 emissions from wheat and rice cropping systems fertilized with urea (U). For the wheat cropping system, using a cambisol, we observed that the application of U with hydroquinone (HQ, a urease inhibitor), U with dicyandiamide (DCD, a nitrification inhibitor) and U with HQ plus DCD decreased the N 2 O emissions by 11.4, 22.3 and 25.1%, respectively. For the rice copping system, using a luvisol, we found that the application of U with HQ, U with DCD and U with HQ plus DCD decreased N 2 O emissions by 10.6, 47.0 and 62.3%, respectively, and CH 4 emissions by 30.1, 53.1 and 58.3%, respectively. In terms of total global warming potential (GWP) a reduction of 61.2% could be realized via the combined addition of HQ and DCD. The addition of wheat straw reduced the activity of HQ and DCD in the rice cropping experiments. In terms of total GWP only a reduction of 30.7% could be achieved. In general, both in upland and flooded conditions, the application of HQ and DCD alone was less effective than HQ in combination with DCD, but not significantly for U plus DCD treatment. Our observations may be further constrained, however, by practical, economic or social problems and should therefore be tested at the scale of a region (e.g. a watershed) and related to an integrated abatement of agricultural N losses. Introduction In Asia the production of anthropogenic reactive N has increased dramatically from 14.4 Tg N yr 1 in 1961 to 67.7 Tg N yr 1 in 2000 (Zheng et al. 2002). An increasing food demand and the lack of effective measures to improve fertilizer N use effi- ciency is one of the main drivers behind the problem of N enrichment in the Asian environ- ment. Rice-wheat rotations are the dominant cropping system in China. In 2001, Chinese wheat and rice production accounted for approximately 40 and 35% of the total production in Asia (FAO 2003), respectively. In 2001, urea fertilizer ac- counted for approximately 60 and 66% of the total fertilizer N used in China (22.4 · 10 6 ton N) and in Asia (46.9 · 10 6 ton N), respectively (FAO 2003). Urea fertilized rice-wheat cropping systems are a large potential source for N 2 O and CH 4 emissions. A possible option to reduce these emissions is the use of urease and nitrification inhibitors in conjunction with the urea fertilizer. Nutrient Cycling in Agroecosystems (2005) 72: 41–49 Ó Springer 2005 DOI 10.1007/s10705-004-7352-4