Nitrate leaching from agricultural production systems threatens groundwater and surface water quality. Grazing of forage crops can result in high inputs of urinary-N and soil compaction from livestock treading. However, the effects of soil compaction from winter grazing on nitrate leaching are poorly understood. The objective of this study was to test the hypothesis that the effects of soil compaction on nitrate leaching after winter grazing depend on rainfall (amount and temporal pattern) and evaporation-regulated soil water content. HYDRUS-1D was used to simulate post-winter grazing drainage and nitrate leaching with five degrees of soil compaction and four factors (i.e. forage crop establishment method, fallow period, climate, and urine addition). Empirical data were obtained from a previous experiment conducted on a moderately well-drained soil (Templeton silt loam, Udic Haplustept) in Canterbury, New Zealand. The results suggested that soil compaction can increase nitrate leaching, and this was more likely to occur in cultivated soils, following high input of urea N, during longer fallow periods and where rainfall is higher during the fallow periods (winter/spring). The increase in nitrate leaching from compaction was mainly attributed to greater drainage as a result of reduced evaporation and a lower capacity to retain water before drainage was triggered. A conceptual model was developed to explain the effect of compaction on drainage during two different phases of soil evaporation that depend on soil water content. This study highlighted the importance of soil water content to determining drainage and nitrate leaching. Therefore, management practices that help to promote soil drying by increasing evaporation (e.g. use no-tillage to establish forage crops to reduce compaction, shallow tillage after winter grazing) and transpiration (e.g. sowing a catch crop earlier) are essential to reducing the risk of drainage and nitrate leaching after winter grazing.

农业生产系统中的硝酸盐浸出威胁着地下水和地表水的质量。牧草作物的放牧会导致大量的尿氮输入和牲畜踩踏造成的土壤板结。然而，人们对冬季放牧造成的土壤压实对硝酸盐淋失的影响知之甚少。本研究的目的是检验冬季放牧后土壤压实对硝酸盐淋失的影响取决于降雨量（数量和时间模式）和蒸发调节的土壤含水量的假设。HYDRUS-1D用于模拟冬后放牧排水和硝酸盐淋溶，土壤压实度为五度和四个因素（即牧草种植方法、休耕期、气候和尿量）。经验数据来自先前在新西兰坎特伯雷的适度排水良好的土壤（Templeton 淤泥壤土，Udic Haplustept）上进行的实验。结果表明，土壤压实可以增加硝酸盐淋失，这更可能发生在耕作土壤中，在高尿素 N 输入后，在较长的休耕期和休耕期（冬季/春季）降雨量较高的地方。压实过程中硝酸盐浸出的增加主要是由于蒸发减少导致排水量增加以及在排水被触发之前保持水分的能力降低。开发了一个概念模型来解释在取决于土壤含水量的土壤蒸发的两个不同阶段期间压实对排水的影响。这项研究强调了土壤含水量对确定排水和硝酸盐淋失的重要性。因此，通过增加蒸发（例如使用免耕来建立饲草作物以减少压实、冬季放牧后浅耕）和蒸腾作用（例如提早播种作物）有助于促进土壤干燥的管理实践对于降低冬季放牧后的排水和硝酸盐淋失。