Crop diversification improves cropping system sustainability: An 8-year on-farm experiment in South-Western France

CONTEXT: Conventional cropping systems in south-western France contribute greatly to the degradation of environmental resources. Crop diversification is considered to be an effective mechanism to increase the sustainability of cropping systems and promote their transition to agroecology. To test this hypothesis, farmers, agricultural advisers and scientists developed a participative co-design project. OBJECTIVE: The main objective was to co-design cropping systems to reduce the use of inputs, experiment with them on farms and assess their sustainability over several years. METHODS: Eight diversified cropping systems were designed during multi-actor co-innovation workshops. These systems were established and monitored for eight years (2010-2017) on two fields on each of eight farms located in areas with different soil and climate conditions. At the end of the eight-year study, the performance of these cropping systems was evaluated using 15 economic, environmental and social indicators. RESULTS AND CONCLUSIONS: Crop diversification improved most of the environmental indicators. Pesticide use decreased by 20-64% in five of the eight systems but increased in the other three, due to production contracts that required systematic applications or in order to control high levels of pest or weed pressure. In parallel, mean energy consumption (-30%), greenhouse gas emissions (-36%) and irrigation water consumption (-43%) decreased significantly after diversification, which helped the systems mitigate and adapt to climate change. The economic performance, however, was more contrasted, with four of the eight farms showing a decrease in seminet margin of 10-35% compared to those of the initial systems, but the other four showing an increase of 5-190%. Production of food energy also generally decreased (by up to 40%) after diversification, mainly due to a decrease in the amount of cereals produced (especially maize). Thus, crop diversification usually improves the environmental sustainability of cropping systems; however, for certain specialised high-value cropping systems, which often have high environmental impacts, it tends to reduce their economic performances.