Reducing nitrate leaching from agricultural land to aquifers has been a high priority concern for more than a half century. This study presents theory and observations of a threshold concentration of nitrate in the root zone (Cmax), which the leachate concentration increases at higher rates with increasing root-zone nitrate concentration. The value of Cmax is derived both by direct results from container experiments with varying nitrogen (N) fertigation and as a calibration parameter in N-transport models beneath commercial agricultural plots. For five different crops, Cmax ranged between 20 and 45 mg L⁻¹ of NO₃–N derived from experiments and models. However, for lettuce (Lactuca sativa L.), which was irrigated with a large leaching fraction, Cmax could not be defined. In crops irrigated and fertilized in the warm/dry season (corn [Zea mays L.] and citrus), the experiments show a dramatic change in leachate-concentration slope, and simulations reveal a wide range of sensitivity of leachate NO₃–N concentration to Cmax. In annual crops irrigated and fertilized in the cool/wet season (e.g., potato [Solanum tuberosum L.] in a Mediterranean climate), the experiments show a distinct Cmax that is less dramatic than that of the summer-irrigated crops in the container experiment and a smaller impact of Cmax in N-transport models. The simulations show that, for summer-irrigated crops, maintaining fertigation at C < Cmax has a significant effect reducing deep leachate concentrations, whereas for the winter annual crops the simulations revealed no threshold effect. It is suggested that for summer-irrigated crops, fertigation below Cmax robustly serves the co-sustainability of intensive agriculture and aquifer water quality; this is also suggested for winter crops, but the benefits are not robust. For short-season, small root-system crops (e.g., lettuce), efforts should be made to detach the crop from the soil.

中文翻译：

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使用阈值硝酸盐根吸收现象维持覆盖含水层的集约化农业

半个多世纪以来，减少从农业用地向含水层浸出的硝酸盐一直是人们高度关注的问题。本研究介绍了根区硝酸盐阈值浓度 ( C max) 的理论和观察结果，随着根区硝酸盐浓度的增加，渗滤液浓度以更高的速率增加。C max的值来自不同氮 (N) 施肥的容器实验的直接结果，以及作为商业农业地块下 N 传输模型中的校准参数。对于五种不同的作物，C max 介于 20 到 45 mg L ^-1的 NO ₃ –N之间，这些范围来自实验和模型。然而，对于生菜（Lactuca sativaL.)，用大浸出率灌溉，C max 无法定义。在暖季/旱季灌溉和施肥的作物（玉米 [ Zea mays L.] 和柑橘）中，实验显示渗滤液浓度斜率发生了显着变化，并且模拟显示渗滤液 NO ₃ –N 浓度的敏感性范围很广至C最大值。在凉爽/潮湿季节灌溉和施肥的一年生作物（例如，地中海气候中的马铃薯 [ Solanum tuberosum L.]）中，实验显示出明显的C max 比容器中的夏季灌溉作物的C max 低实验和C的较小影响N-传输模型中的最大值。模拟表明，对于夏季灌溉作物，将施肥维持在C  <  C max 具有显着降低深度渗滤液浓度的效果，而对于冬季一年生作物，模拟显示没有阈值效应。建议对于夏季灌溉作物，低于C max 的施肥有力地促进了集约化农业和含水层水质的共同可持续性；这也建议用于冬季作物，但收益并不强。对于短季、小型根系作物（如生菜），应努力将作物与土壤分离。