Cover crop (CC) mixtures including both legume and non-legume species have the potential to reduce nitrate leaching and increase N availability in the system through biological N₂ fixation (BNF). However, the provision of multiple services depends on the biomass expression of functionally diverse species. Cover crop growth can be manipulated through management, but more knowledge is needed on species expression, and the effects on nitrate leaching and BNF. We investigated this in a long-term organic crop rotation experiment, where an undersown legume-based CC mixture, composed of perennial ryegrass (Lolium perenne L.), chicory (Chicorium intybus L.), white clover (Trifolium repens L.) and red clover (Trifolium pratense L.), was grown under different cropping system and fertility management in three consecutive years. We found a linear complementary relation between legume and non-legume biomass when CC growth was the greatest. Non-legume biomass was high under non-N-limiting conditions, while legume biomass and N input via BNF were high where the risk of nitrate leaching was low, as shown by the low and stable nitrate leaching above a threshold of 0.4 Mg clover DM ha⁻¹. Above this threshold, the percentage of N derived from the atmosphere (%Ndfa) was high and stable (91 %), while lower and more variable with lower legume biomass. Overall, our results show that legume-based CC mixtures are self-regulating in terms of nitrate leaching reduction and N input via BNF.

包括豆科植物和非豆科植物在内的农作物混合物均具有通过生物固氮₂（BNF）减少硝酸盐淋失并增加系统中氮素利用率的潜力。但是，提供多种服务取决于功能多样的物种的生物量表达。覆盖作物的生长可以通过管理来控制，但是还需要更多有关物种表达的知识，以及对硝酸盐浸出和BNF的影响。我们在一项长期的有机作物轮作试验中对此进行了调查，该试验中使用的是一种未播种的豆科植物CC混合物，该混合物由多年生黑麦草（Lolium perenne L.），菊苣（Chicorium intybus L.），白三叶草（Trifolium repens L.）和红三叶草（白三叶L.），已连续三年在不同的种植系统和肥力管理下生长。当CC增长最大时，我们发现豆类和非豆类生物量之间存在线性互补关系。在非-N限制条件下，非豆类生物量较高，而在硝酸盐浸出风险较低的情况下，豆类生物量和通过BNF的氮输入较高，这表明硝酸盐浸出量低且稳定（高于0.4 Mg三叶草DM） ha ^-1。高于此阈值，来自大气的氮百分比（％Ndfa）高而稳定（91％），而豆类生物量越低，氮的百分比就越高。总体而言，我们的研究结果表明，基于豆类的CC混合物在减少硝酸盐浸出和通过BNF输入氮方面具有自我调节作用。