Organic agriculture could achieve the objectives of sustainable agriculture by banning the use of synthetic fertilizers and pesticides. However, organic crops generally show lower performances than conventional ones. In France, organic winter wheat production is characterized by low grain protein content. There is a crucial need for better understanding the variability of grain protein content, because millers require batches with values over 10.5% of dry matter. Here, a regional agronomic diagnosis was carried out to identify the limiting factors and crop management practices explaining the variability of grain protein content. The studied field network was a set of 51 organic winter wheat plots in south-eastern France. The mixed-model method was used for identifying and ranking the limiting factors and the crop management practices responsible for variation in limiting factors. Our results show that the grain protein content variation was mostly explained by the baking quality grade of the cultivar, crop nitrogen status and weed density at flowering. There was a positive correlation between grain protein content and both crop nitrogen status and weed density. To a lesser extent, climatic factors also explained grain protein content variability. A lower water stress increased grain protein content, whereas an increase in the photothermal quotient and daily temperature over 25 °C reduced grain protein content. In south-eastern France, grain protein content of organic winter wheat could be increased by improving fertilization management, using an improved baking quality grade cultivar, choosing a legume fodder crop as preceding crop, or by avoiding late sowing dates.

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限制法国东南部有机冬小麦籽粒蛋白质含量的因素：一种混合模型方法

有机农业可以通过禁止使用合成肥料和农药来实现可持续农业的目标。然而，有机作物通常表现出比常规作物低的性能。在法国，有机冬小麦的生产特点是谷物蛋白质含量低。迫切需要更好地了解谷物蛋白质含量的可变性，因为制粉者需要一批干物质含量超过10.5％的批次。在这里，进行了区域农艺学诊断，以确定限制因素和解释谷物蛋白含量变异性的作物管理实践。研究的田间网络是法国东南部的一组51个有机冬小麦田。混合模型方法用于识别和排序限制因素，并对造成限制因素变化的作物管理实践进行分类。我们的结果表明，籽粒蛋白质含量的变化主要由品种的烘烤质量等级，作物氮素状况和开花时的杂草密度所解释。谷物蛋白质含量与作物氮素状况和杂草密度之间呈正相关。在较小程度上，气候因素也解释了谷物蛋白质含量的变异性。较低的水分胁迫增加了谷物蛋白质含量，而光热商和日温度升高超过25°C则降低了谷物蛋白质含量。在法国东南部，可以通过改善施肥管理来提高有机冬小麦的谷物蛋白含量，