Abstract The vast majority (82 %) of the earth’s cultivated area is not irrigated, and half is in semi-arid regions where water tends to limit crop growth. In dryland semi-arid agroecosystems, any precipitation not transpired indicates crop yield that is below potential. Precipitation that is partitioned to deep percolation can transport nitrate out of the root zone, reducing nitrogen use efficiency and potentially contaminating groundwater. To mitigate loss of crop yield to drought, the practice of chemical summer-fallow (suppressing plant growth for a full growing season with herbicide) has been common in semi-arid regions to store water for the following growing season. However, precipitation losses during fallow tend to exceed the amount of precipitation stored, and fallow tends to increase nitrate leaching. We present model simulations informed by field observations that explore the interaction of crop rotation, weather, and soils as controls on precipitation partitioning and nitrate leaching. Simulations reveal that high intensity precipitation periods produce hot moments of deep percolation and nitrate leaching such that 54 % of deep percolation and 56 % of leaching occurs in two of 14 model years. Simulations indicate that thin soils (having limited water storage capacity) produce hot spots for deep percolation and nitrate leaching such that thinner soils ( 100 cm). The practice of fallow facilitates mineralization of soil organic nitrogen to nitrate and increases deep percolation, magnifying the interaction of hot moments and hot spots. Simulations suggest that a field with fallow in rotation once every three years experiences 55 % of its deep percolation and 43 % of its leaching losses during fallow years.

中文翻译：

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旱地农业土壤的水分和硝酸盐流失受管理、土壤和天气的控制

摘要 地球上绝大多数（82%）的耕地没有灌溉，其中一半位于半干旱地区，水往往限制了作物的生长。在旱地半干旱农业生态系统中，任何未蒸发的降水都表明作物产量低于潜力。分配到深层渗透的降水可以将硝酸盐带出根区，降低氮的使用效率并可能污染地下水。为了减轻干旱造成的作物产量损失，半干旱地区普遍采用化学夏令时（用除草剂抑制整个生长季节的植物生长），以便为下一个生长季节储存水分。然而，休耕期间的降水损失往往超过储存的降水量，休耕往往会增加硝酸盐的浸出。我们提供了由实地观察提供的模型模拟，探索作物轮作、天气和土壤的相互作用，作为对降水分配和硝酸盐浸出的控制。模拟表明，高强度降水期会产生深度渗透和硝酸盐浸出的热时刻，因此 54% 的深度渗透和 56% 的浸出发生在 14 个模型年中的两个年份。模拟表明，薄土（储水能力有限）会产生深层渗透和硝酸盐浸出的热点，从而使较薄的土壤（100 厘米）。休耕的做法有利于土壤有机氮矿化为硝酸盐并增加深层渗透，放大热点和热点的相互作用。