Abstract Weeds are often solely considered with a negative viewpoint, but they may also provide services for agroecosystems. Especially, the residual weed flora that is tolerated by integrated crop protection may contribute to a reduction of nitrate leaching and soil erosion during the summer and autumn fallow. To date, the determinants underlying these environmental weed benefits are largely unknown. The present study developed new indicators to account for the potential beneficial role of annual weed flora to reduce nitrate leaching and soil erosion at the field scale, and then calculated them from the outputs of a weed dynamics model. The aim was to analyse which cropping systems facilitate residual weed flora to reduce nitrate leaching and soil erosion, while minimizing negative weed impacts on crop production. When developing the indicators, the potential weed-based reduction of nitrate leaching was considered to increase with both the growth of the weed flora and the weed species potential to take up nitrogen; the potential weed-based reduction of soil erosion was assumed to increase with soil cover by weeds when soil cover by cash crops was low. Our simulation study included 259 arable cropping systems (covering a wide range of herbicide and tillage intensity, with each cropping system simulated over 28 years and repeated 10 times with 10 different weather series) in which the dynamics of 25 annual weed species was simulated. Simulations showed that the cropping systems promoting a high potential weed-based reduction of nitrate leaching were generally also those with a high potential weed-based reduction of soil erosion, pointing to a compatibility between these benefits provided by the weed flora. However, the cropping systems promoting these environmental benefits were generally also those that presented the highest crop yield losses. Tillage and crop rotation were identified as the cultural techniques with the greatest influence on the potential weed-based reduction of nitrate leaching and soil erosion, while herbicides had a more limited effect. Most of the studied cropping systems (representing “real situations” in which farmers or experimenters make the decisions about crop rotations and cultural techniques) tended to favour low crop yield losses rather than high weed-based environmental benefits. Interestingly, a few systems achieved both objectives. Systems that achieved relatively low crop yield losses and high weed-based environmental benefits mainly combined infrequent superficial tillage operations, with a low proportion of winter crops in the rotation and a very low tillage depth. Finally, only a few weed traits determined the role of the weed flora to potentially reduce nitrate leaching and soil erosion. They were seed traits (seed lipid content, seed area per weight and seed coat thickness), driving the early and fast appearance of the weed canopy after weed seed shed. This suggests that, for annual weed species, a high weed flora potential to reduce nitrate leaching and soil erosion is not restricted to specific weed species able to take up nitrogen and cover soil. Thus, our simulation study indicates that such a high potential to reduce nitrate leaching and soil erosion could therefore be reached in very different agroecosystems in terms of weed seed bank.

中文翻译：

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残留的杂草可以在哪些种植系统中减少硝酸盐浸出和土壤侵蚀？

摘要 杂草通常只被认为是消极的，但它们也可能为农业生态系统提供服务。特别是，综合作物保护所容忍的残留杂草群可能有助于减少夏季和秋季休耕期间的硝酸盐浸出和土壤侵蚀。迄今为止，这些环境杂草效益的决定因素在很大程度上是未知的。本研究开发了新的指标，以说明一年生杂草菌群在减少田间硝酸盐浸出和土壤侵蚀方面的潜在有益作用，然后根据杂草动力学模型的输出计算它们。目的是分析哪些种植系统有利于残留的杂草菌群，以减少硝酸盐浸出和土壤侵蚀，同时最大限度地减少杂草对作物生产的负面影响。在制定指标时，杂草对硝酸盐浸出的潜在减少被认为随着杂草菌群的生长和杂草种类吸收氮的潜力而增加；当经济作物的土壤覆盖率较低时，假设杂草对土壤侵蚀的潜在减少会随着杂草覆盖率的增加而增加。我们的模拟研究包括 259 个耕地种植系统（涵盖广泛的除草剂和耕作强度，每个种植系统模拟了 28 年以上，并在 10 个不同的天气系列中重复 10 次），其中模拟了 25 种一年生杂草的动态。模拟表明，促进以杂草为基础的高潜力减少硝酸盐浸出的种植系统通常也具有以杂草为基础的高潜力减少土壤侵蚀的种植系统，指出杂草植物群提供的这些好处之间的兼容性。然而，促进这些环境效益的种植系统通常也是那些表现出最高作物产量损失的系统。耕作和轮作被确定为对潜在的以杂草为基础的硝酸盐浸出和土壤侵蚀的减少影响最大的栽培技术，而除草剂的作用更为有限。大多数研究的种植系统（代表农民或试验者做出关于作物轮作和栽培技术决定的“真实情况”）倾向于低作物产量损失，而不是高杂草环境效益。有趣的是，一些系统实现了这两个目标。实现相对较低的作物产量损失和基于杂草的高环境效益的系统主要结合了不频繁的浅耕作业、轮作中冬季作物的比例低和耕作深度非常低。最后，只有少数杂草性状决定了杂草菌群在潜在减少硝酸盐浸出和土壤侵蚀方面的作用。它们是种子性状（种子脂质含量、每单位重量的种子面积和种皮厚度），在杂草种子脱落后推动杂草冠层的早期和快速出现。这表明，对于一年生杂草种类，减少硝酸盐浸出和土壤侵蚀的高杂草群落潜力并不限于能够吸收氮和覆盖土壤的特定杂草种类。因此，