Is integrated weed management efficient for reducing environmental impacts of cropping systems ? A case study based on life cycle assessment
Résumé
Integrated weed management in arable crops relies on the combination of various measures for preventing, avoiding and suppressing weeds, with the aim of reducing the reliance on herbicides and their environmental impacts. As IWM requires potentially deep changes in the cropping systems, modifying e.g. the crop sequence, the strategies for soil tillage and eventually introducing mechanical weeding, it is important to perform comprehensive evaluations of IWM-based cropping system prototypes. In this study, a life cycle assessment method was used to compute several environmental impacts for four variants of IWM-based cropping system tested over a pluri-annual experiment, and compared with a standard reference. When expressed per unit of cultivated area, most environmental indicators were improved in IWM-based systems, including the energy input, greenhouse gas emission, eutrophication and acidification, and ecotoxicity and human toxicity. In-field fuel consumption was a rather minor contribution to the overall energy demand and to global warming. The ranking of the tested cropping systems was different when the indicators were expressed per unit of harvested agricultural goods or per unit of farmer's income. With these two functional units, the differences among systems tended to be weaker, and some indicators of environmental impacts were higher in IWM-based systems. Indicators focusing on biodiversity and soil quality displayed few differences among systems.