A cost-benefit analysis of rice field winter flooding for conservation purposes in Camargue, Southern France

Rice plants have a high silica content, which prevents rice straw from being used as a compostable bi-product in the same way as that from wheat and many other crops. The most common post-harvest practice in rice fields in France is to burn and then plough the fields. Flooding harvested fields during winter may create agronomical and environmental advantages, but the economic profitability of the practice has not been adequately studied. We used a cost-benefit analysis to explore six possible agricultural scenarios during the rice intercrop period, at the scale of individual farms and of society as a whole. All scenarios were economically realistic for the farmer (benefits-to costs ratios > 1), except current burning-ploughing which was just below economic equilibrium (B/C = 0.93). The most beneficial however was harvesting rice in flooded fields, which saved irrigation pumping costs. Similar results existed at the society level, and burning-ploughing was again clearly unacceptable (B/C = 0.73), largely because of greenhouse gas emissions and the absence of ecosystem benefits made available by flooding fields. Harvesting rice in flooded conditions and maintaining water in the fields afterwards was the most profitable option, and remained so during our sensitivity analysis when a wide range of variable evaluations were simulated. More than burning and ploughing, flooding rice fields facilitates straw and weed seed decomposition and creates a range of environmental benefits including the provision of extensive foraging habitat to wintering waterfowl. Our results suggest that post-harvest flooding of rice fields in France is economically realistic for farmers and the most beneficial practice for society.