Cover crops are increasingly being used for weed management, and planting them as diverse mixtures has become an increasingly popular strategy for their implementation. While ecological theory suggests that cover crop mixtures should be more weed suppressive than cover crop monocultures, few experiments have explicitly tested this for more than a single temporal niche. We assessed the effects of cover crop mixtures (5- or 6-species and 14-species mixtures) and monocultures on weed abundance (weed biomass) and weed suppression at the time of cover crop termination. Separate experiments were conducted in Madbury, NH, from 2014 to 2017 for each of three temporal cover-cropping niches: summer (spring planting–summer termination), fall (summer planting–fall termination), and spring (fall planting–subsequent spring termination). Regardless of temporal niche, mixtures were never more weed suppressive than the most weed-suppressive cover crop grown as a monoculture, and the more diverse mixture (14 species) never outperformed the less diverse mixture. Mean weed-suppression levels of the best-performing monocultures in each temporal niche ranged from 97% to 98% for buckwheat (Fagopyrum esculentum Moench) in the summer niche and forage radish (Raphanus sativus L. var. niger J. Kern.) in the fall niche, and 83% to 100% for triticale (×Triticosecale Wittm. ex A. Camus [Secale × Triticum]) in the winter–spring niche. In comparison, weed-suppression levels for the mixtures ranged from 66% to 97%, 70% to 90%, and 67% to 99% in the summer, fall, and spring niches, respectively. Stability of weed suppression, measured as the coefficient of variation, was two to six times greater in the best-performing monoculture compared with the most stable mixture, depending on the temporal niche. Results of this study suggest that when weed suppression is the sole objective, farmers are more likely to achieve better results planting the most weed-suppressive cover crop as a monoculture than a mixture.

中文翻译：

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覆盖作物混合物在抑制杂草方面是否比覆盖作物单一栽培更好？

覆盖作物越来越多地用于杂草管理，将它们作为多种混合物种植已成为一种越来越受欢迎的实施策略。虽然生态理论表明，覆盖作物混合物应该比覆盖作物单一栽培更能抑制杂草，但很少有实验明确测试这一点，而不是单一的时间生态位。我们评估了覆盖作物混合物（5 种或 6 种和 14 种混合物）和单一栽培对覆盖作物终止时杂草丰度（杂草生物量）和杂草抑制的影响。从 2014 年到 2017 年，在新罕布什尔州麦德伯里对三个临时覆盖种植生态位中的每一个进行了单独的实验：夏季（春季种植-夏季终止）、秋季（夏季种植-秋季终止）和春季（秋季种植-随后的春季终止） ）。无论时间利基如何，混合物从来没有比作为单一栽培种植的最能抑制杂草的覆盖作物更能抑制杂草，而且更多样化的混合物（14种）从来没有超过多样性较低的混合物。荞麦在每个时间生态位中表现最好的单一栽培的平均杂草抑制水平从 97% 到 98% 不等。荞麦Moench）在夏季小生境和草料萝卜（萝卜L.变种。尼日尔J. Kern.）在秋季利基市​​场，83% 到 100% 用于小黑麦（×小​​麦鳞片威特姆。前 A.加缪 [黑麦×小麦]）在冬春季生态位。相比之下，在夏季、秋季和春季生态位中，混合物的杂草抑制水平分别为 66% 至 97%、70% 至 90% 和 67% 至 99%。与最稳定的混合物相比，以变异系数衡量的杂草抑制稳定性在表现最佳的单一栽培中要高出两到六倍，具体取决于时间生态位。这项研究的结果表明，当杂草抑制是唯一目标时，农民将最能抑制杂草的覆盖作物种植为单一种植而不是混合种植更有可能取得更好的结果。