High N2O variations induced by agricultural practices in integrated weed management systems

Integrated weed management aims to decrease the dependence of cropping systems on herbicides by using a combination of several agricultural practices. Environmental impacts of individual practices under various conditions are already known. However, there is scarce knowledge on the impact of combining several practices. Therefore, we studied N2O emissions of weed management cropping systems that use differing practices such as crop diversity, tillage, and herbicide pressure, during about 1 year. Data were compared with a conventionally managed cropping system. Results were also simulated using the NOE model. Results show a large variation of N2O emissions, ranging from 177 g N2O-N/ha for intensive tillage integrated weed management to 362 g N2ON/ha for the conventional cropping system, 777 g N2O-N/ha for the no herbicide cropping system and 5226 g N2O-N/ha for no-till integrated weed management. Most N2O emissions occurred in spring, despite the absence of fertilizing related N2O peaks. The lowest emissions occurred in autumn and winter. Emissions are explained by interactions between specific soil potential denitrification rate, soil bulk density, temperature, soil water, and inorganic N contents. N2O emissions are accurately predicted by the model NOE, with a global Nash-Sutcliffe coefficient of efficiency equal to 0.80.