The midwestern United States is a highly productive agricultural region, and extended crop-free periods in winter/spring can result in nitrogen (N) and phosphorus (P) losses to waterways that degrade downstream water quality. Planting winter cover crops can improve soil health while reducing nutrient leaching from farm fields during the fallow period. In this study, we used linear mixed effects models and multivariate statistics to determine the effect of cover crops on soil nutrients by comparing fields with cover crops (n = 9) versus those without (n = 6) in two Indiana agricultural watersheds: the Shatto Ditch Watershed, which had >60% of croppable acres in winter cover crops, and the Kirkpatrick Ditch Watershed, which had ∼20%. We found that cover crops decreased soil nitrate-N by >50% and that the magnitude of reduction was related to the amount of cover crop biomass. In contrast, cover crops had variable effects on water extractable P and Mehlich III soil test P. Finally, cover crop biomass significantly increased soil N mineralization and nitrification rates, demonstrating that cover crops have the potential to supply bioavailable N to cash crop after termination. Our study showed that widespread implementation of winter cover crops holds considerable promise for reducing nutrient loss and improving soil health. The degree to which these results are generalizable across other systems depends on factors such as climate, soil characteristics, and past and current agronomic practices.

中文翻译：

---

冬季覆盖作物对印第安纳州两个中耕流域土壤养分的影响

美国中西部是一个高产农业区，冬季/春季延长无作物期会导致水道中的氮 (N) 和磷 (P) 损失，从而降低下游水质。种植冬季覆盖作物可以改善土壤健康，同时减少休耕期间农田的养分流失。在这项研究中，我们使用线性混合效应模型和多变量统计通过用覆盖作物（比较字段，以确定对土壤养分覆盖作物的效果Ñ  = 9）与那些没有（Ñ = 6) 在印第安纳州的两个农业流域：Shatto Ditch 流域，其冬季覆盖作物的可耕地面积超过 60%，而 Kirkpatrick Ditch 流域的可种植面积约为 20%。我们发现覆盖作物使土壤硝酸盐氮减少了 50% 以上，减少的幅度与覆盖作物生物量有关。相比之下，覆盖作物对可提取水磷和 Mehlich III 土壤测试 P 有不同的影响。最后，覆盖作物生物量显着增加了土壤氮矿化和硝化率，表明覆盖作物有潜力在终止后为经济作物提供生物可利用的氮。我们的研究表明，冬季覆盖作物的广泛实施对于减少养分流失和改善土壤健康具有相当大的希望。