Controlled drainage (CD), sometimes called drainage water management, is a practice whereby the drainage system outflow is managed during specific periods to retain more water in the field. Although CD has been shown to reduce downstream nitrate-N (NO₃^--N) load, seasonal patterns have been less consistent which can potentially impact the effectiveness of conservation practices. The main objective of this study was to assess the regional and seasonal impact of conventional free drainage (FD) and CD on drainage flow and nitrate-N load. Using experimental data from ongoing and historical CD experiments across the Corn Belt and in North Carolina, we evaluated subsurface drain flow, nitrate-N load, and performance of CD systems. Across the data set and regions, there was little difference in annual flow from FD conditions. Seasonally, more northern and western sites experienced a greater percentage of the annual flow occurring in the spring. There was no nitrate-N concentration reduction with CD. Flow and nitrate-N load reductions with CD did not vary by plant hardiness zone across the region, but the season with the greatest reduction did shift from winter to spring moving north and west in the study area. Absolute flow reductions (in mm) were similar regardless of precipitation category. Consequently, the percent reduction was lower as the amount of precipitation (category) increased. Overall, this analysis found CD to be an effective practice for reducing drain flow and nitrate-N loading directly delivered by the drains to downstream water bodies across the region.

受控排水 (CD)，有时也称为排水管理，是一种在特定时期管理排水系统流出量以在田间保留更多水的做法。虽然 CD 已被证明可以减少下游的硝酸盐 -N（NO ₃ ^--N) 负载，季节性模式不太一致，这可能会影响保护实践的有效性。本研究的主要目的是评估常规自由排水 (FD) 和 CD 对排水流量和硝酸盐氮负荷的区域和季节性影响。使用来自整个玉米带和北卡罗来纳州正在进行和历史 CD 实验的实验数据，我们评估了地下排水流、硝酸盐-N 负载和 CD 系统的性能。在整个数据集和区域中，FD 条件下的年流量几乎没有差异。季节性地，更多的北部和西部站点经历了更大比例的春季年流量。CD 没有降低硝酸盐-N 浓度。CD 的流量和硝酸盐 N 负荷减少不会因整个地区的植物抗寒区而异，但减少幅度最大的季节确实从冬季转移到春季，研究区向北和向西移动。无论降水类别如何，绝对流量减少（以毫米为单位）都是相似的。因此，随着降水量（类别）的增加，减少的百分比较低。总体而言，该分析发现 CD 是一种有效的做法，可减少排水管直接输送到该地区下游水体的排水管流量和硝酸盐氮负荷。