Crop Diversification as a Mechanism for Improving the Sustainability of Cropping Systems : An 8-Year On-Farm Experiment Involving Farmers, Advisers and Scientists in South-Western France

Crop diversification is considered to be an effective mechanism for increasing the sustainability of cropping systems and promoting their agroecological transition. To test this hypothesis for common cropping systems in south-western France that contribute to degradation of environmental resources, farmers, agricultural advisers and scientists developed a participative co-design project that led to the design of eight diversified cropping systems. 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. 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 to 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 semi-net margin of 10-35% compared to those of the initial systems. 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 but for certain specialised high-value cropping systems, which often have high environmental impacts, tends to reduce their economic sustainability