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 meth od over a 1-year period in a cultivated field subjected to different a gricultural 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) durin g the autumn, 16-56 g N ha(-1) day(-1) in winter after a lengthy perio d of freezing, 0.5-70 g N ha(-1) day(-1) during the spring and lower e missions during the summer. The type of crop had little impact on the level of N2O emission. These emissions were a little higher under whea t during the autumn in relation to an higher soil NO3-, content, but t he 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 fertiliz er affected N2O emissions during the month following fertilizer applic ation, with higher emissions in the case of NH4NO3 and (NH4)(2)SO4, an d 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% w ith the form of N applied, suggesting that controlling this agricultur al factor would not be an efficient way of limiting N2O emissions unde r certain climatic and pedological situations.