Data_Sheet_3_Carbon Dioxide Emission and Soil Sequestration for the French Agro-Food System: Present and Prospective Scenarios.xlsx

France is a major agricultural power, characterized by a high degree of regional specialization, either in stockless cash crop farming, exporting most of its intensive cereal production, or in intensive livestock farming highly dependent on foreign feed imports. This agricultural model is characterized by wide nutrient and carbon cycle opening and severe environmental pollution. Based on the nutrient accounting GRAFS model, two contrasted scenarios for the French agricultural system at the 2050 horizon have recently been designed and evaluated for their capacity to meet both the national population's food demand and environmental standards in terms of water pollution. The first scenario (O/S, for opening and specialization) assumes the continuation of the current trends of intensification, specialization, and opening to international markets. The second one (A/R/D, for autonomy, reconnection, and demitarian diet) assumes a radical change toward organic farming with diversification of crop rotations, reconnection of crop and livestock farming, and reduction of the proportion of animal proteins in the human diet. Herein we calculate the budget of CO2 emissions and C sequestration in soils of these two scenarios compared with the current situation of the French agro-food system, by coupling the GRAFS and AMG models. These simulations reveal that the overall CO2 emissions balance of the O/S scenario is far higher than those of the A/R/D, namely because of the emissions associated with mineral fertilizer manufacture, and imported feed and mechanization of land management requiring a large amount of fossil fuel. As the organic carbon content of the soil is known to be highly path-dependent (in the sense that it is the inheritance of previous land use practices), we tested the effect of two rates of implementation of the two scenarios and evaluated the response time of the C soil store, which is of the order of two decades or more. This reveals that after about two-three decades following the implementation of a scenario, an equilibrium is reached with no more net soil C emission nor sequestration.

法国作为农业大国，其特征在于高度的区域专业化，无论是以无畜的现金作物耕作为主，出口大部分集约化谷物生产，还是以高度依赖外国饲料进口的集约化畜牧业。这一农业模式以广泛的营养和碳循环敞开及严重的环境污染为特征。基于营养会计GRAFS模型，近期已针对2050年远景设计并评估了两种对比鲜明的法国农业系统情景，以评估其满足国家人口粮食需求及在水资源污染方面达到环境标准的潜力。第一种情景（O/S，代表敞开与专业化）假定当前集约化、专业化和对外开放的趋势将持续。第二种情景（A/R/D，代表自主、重连和减少肉食摄入）假定向有机农业的彻底转变，包括作物轮作的多样化、作物与畜牧业的重连以及人类饮食中动物蛋白比例的减少。在此，我们通过耦合GRAFS和AMG模型，计算了这两种情景与法国农业食品系统当前状况相比的二氧化碳排放和土壤碳封存预算。这些模拟显示，O/S情景的整体二氧化碳排放平衡远高于A/R/D情景，这主要是由于与矿物肥料制造、进口饲料和土地管理机械化相关的排放，这些活动需要大量的化石燃料。鉴于土壤有机碳含量众所周知具有高度路径依赖性（即在意义上，它是先前土地利用实践的继承），我们测试了两种实施速率对两种情景的影响，并评估了碳土壤储存库的响应时间，该响应时间约为二十年或更长。这表明，在实施一种情景约二十至三十年后，将达到一个平衡状态，此时土壤不再有净碳排放或封存。