Winter cover crops reduce nitrate loss in an agricultural watershed in the central U.S
Winter cover crops reduce nitrate loss in an agricultural watershed in the central U.S
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DOI：
10.1016/j.agee.2018.07.004
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发表时间：
2018-10-01
影响因子：
6.6
通讯作者：
Royer, Todd V.
中科院分区：
文献类型：
--
作者：
Hanrahan, Brittany R.;Tank, Jennifer L.;Royer, Todd V.
美国中西部的农业用地是造成墨西哥湾北方反复缺氧的氮（N）的主要来源。尽管努力减少损失，从瓷砖排水，整个玉米带农业流域的N出口持续存在。使用有效的农业保护措施，可以减少氮素损失的领域，但鲜为人知的是如何现场规模的实施将转化为流域规模的减少氮素出口。在这项研究中，我们使用了一种高空间和时间分辨率的采样方法，以量化瓷砖排水负荷和流域出口的硝酸盐（NO3--N）种植覆盖作物后的变化> 60%的可耕地面积在一个小的，农业流域。我们发现，中位数NO3--N的损失，从瓷砖排水领域覆盖作物比瓷砖排水领域没有覆盖作物在冬季/春季低69-90%。测得的瞬时流量的主要驱动程序的NO-3-N的损失从瓷砖排水，虽然结果表明，这种关系不同的瓷砖和没有覆盖作物在春季。覆盖作物在田间尺度的签名是明显的流域NO3--N的出口，特别是在流量升高的时候，在流量升高的情况下，平均每日NO3--N的出口是18-22%，在流域规模种植覆盖作物的年份相比，没有。然而，流域NO3--N出口的变化小于所观察到的瓷砖排水负荷的减少。结果表明，瓷砖排水量的减少直接反映了覆盖作物的影响，而流域出口集成了过去和现在的管理，最终复杂化的尝试，以区分在更大的空间尺度上的保护工作的效果。
Agricultural land use in the Midwestern U.S. is the major source of nitrogen (N) causing recurring hypoxia in the northern Gulf of Mexico. Despite efforts to reduce losses, N export from tile-drained, agricultural watersheds throughout the Corn Belt persists. The use of effective agricultural conservation practices can reduce N loss from fields, yet little is known about how field-scale implementation will translate into watershed-scale reductions in N export. In this study, we used a sampling approach with high spatial and temporal resolution to quantify changes in tile drain load and watershed export of nitrate (NO3--N) after planting cover crops on > 60% of croppable acres in a small, agricultural watershed. We found that median NO3--N losses from tiles draining fields with cover crops were 69-90% lower than tiles draining fields without cover crops during winter/spring. Measured instantaneous flow was the major driver of NO-3-N losses from tile drains, though results suggest that this relationship differed between tiles with and without cover crops in spring. The signature of cover crops at the field-scale was evident in watershed NO3--N export, particularly during times of elevated flows; median daily NO3--N exported in elevated flows was 18-22% lower during years with watershed-scale planting of cover crops compared to years without. Nevertheless, changes in watershed NO3--N export were smaller than the observed reductions in tile drain loads. Results indicate that tile drain reductions directly reflected the influence of cover crops at the field-scale while watershed export integrated both past and present management, ultimately complicating attempts to distinguish the effect of conservation efforts at larger spatial scales.