J Environ Qual. 2019 Jul;48(4):907-914. doi: 10.2134/jeq2018.08.0307.
Cover crops (CC) have both agronomic and environmental benefits but also have the potential to increase losses of dissolved reactive P after freeze-thaw cycles (FTC). This field study, conducted over one nongrowing season (NGS) in Ontario, Canada, characterized water-extractable P (WEP) content in different CC species and compared observed changes in plant WEP content with changes in P content in soil, surface runoff, and shallow groundwater (5-25 cm). Five plots (0.4 ha) of cereal rye ( L.), oilseed radish ( L. var. Metzg Stokes), oat ( L.), and hairy vetch ( Roth) were established after winter wheat ( L.) harvest. Throughout the NGS (October-April), CC shoot tissues and surface soil were routinely sampled for WEP analyses, and groundwater and runoff water samples were collected after rain and snowmelt. Responses to FTC varied among CC species, with P released from frost-intolerant species but not frost-tolerant species. Although CC released P, the top 5 cm of soil contained greater WEP than plants at all times, and the changing WEP content in CC over the NGS was not reflected in soil or water P concentrations. These results suggest that the degree of frost exposure should be considered in the selection of CC species in cold regions; however, in temperate regions with snow cover that insulates the soil surface from heavy frost, P release from vegetation may not lead to increased P loss in runoff.
覆盖作物 (CC) 具有农业和环境效益，但也有可能在冻融循环 (FTC) 后增加溶解反应性磷的损失。这项在加拿大安大略省进行的非生长季节 (NGS) 的实地研究，描述了不同 CC 物种的水可提取磷 (WEP) 含量，并比较了观察到的植物 WEP 含量变化与土壤、地表径流和浅层地下水 (5-25 cm) 中磷含量的变化。在冬小麦 ( L.) 收获后，建立了五个试验区 (0.4 公顷)，种植了黑麦 ( L.)、油菜萝卜 ( L. var. Metzg Stokes)、燕麦 ( L.) 和毛野豌豆 ( Roth)。在整个 NGS（10 月至 4 月）期间，常规采集 CC 茎叶和表层土壤进行 WEP 分析，并在雨后和融雪后收集地下水和径流水样。FTC 对 CC 物种的反应各不相同，不耐寒物种释放磷，但耐寒物种不释放磷。尽管 CC 释放了磷，但在任何时候，土壤表层 5 厘米处的 WEP 含量都大于植物，CC 在 NGS 期间的 WEP 含量变化并未反映在土壤或水中的磷浓度中。这些结果表明，在寒冷地区选择 CC 物种时，应考虑霜冻暴露程度；然而，在有积雪覆盖的温带地区，土壤表面免受严重霜冻的影响，植被释放的磷可能不会导致径流中磷的损失增加。
