Influence of different agricultural practices (type of crop, form of N-fertilizer) on soil nitrous oxide emissions

N2O emissions were periodically measured using the static chamber method over a 1-year period in a cultivated field subjected to different agricultural practices including the type of N fertilizer (NH4NO3, (NH4)(2)SO4: CO(NH2)(2) or KNO3 and the type of crop (rapeseed and winter wheat). N2O emissions exhibited the same seasonal pattern whatever the treatment, with emissions between 1.5 and 15 g N ha(-1) day(-1) during the autumn, 16-56 g N ha(-1) day(-1) in winter after a lengthy period of freezing, 0.5-70 g N ha(-1) day(-1) during the spring and lower emissions during the summer. The type of crop had little impact on the level of N2O emission. These emissions were a little higher under wheat during the autumn in relation to an higher soil NO3-, content, but the level of emissions was similar over a 7-month period (2163 and 2093 g N ha(-1) for rape, and wheat, respectively). The form of N fertilizer affected N2O emissions during the month following fertilizer application, with higher emissions in the case of NH4NO3 and (NH4)(2)SO4, and a different temporal pattern of emissions after CO(NH2)2 application. The proportion of applied N lost as N2O varied from 0.42% to 0.55% with the form of N applied, suggesting that controlling this agricultural factor would not be an efficient way of limiting N2O emissions under certain climatic and pedological situations.