Abstract Rice (Oryza sativa) has one of highest applied water footprints of any crop, due in many cases to high percolation and lateral seepage rates in flooded rice fields. Better understanding the magnitude and variability of these subsurface water flows and their contribution to the rice field water balance is critical for efforts to reduce the water footprint of rice production and to limit the transport of pollutants to surface water and groundwater. Percolation was directly measured in eight direct-seeded California rice fields that ranged from 20 to 61% clay and a complete water balance was developed for three of these fields. For these latter fields, directly measured percolation rates were compared to percolation calculated with Darcy’s law, and combined percolation and lateral seepage calculated as the residual of a water balance was compared to directly measured values. Across eight fields, cumulative percolation over the growing season ranged from 0.04 to 6.95 cm season−1. The mean cumulative percolation for the three water balance fields was 2.1 cm based on direct measurements compared to 3.2 cm based on Darcy’s law calculations. Combined percolation and lateral seepage calculated as the residual term of a water balance for the three fields was 17.1 cm, compared to 4.4 cm based on direct measurements, corresponding to 13.2 % and 3.4 % of water inputs, respectively (inputs were 98–99 % from irrigation). Based on these results, water management strategies that remove floodwater (e.g. alternate wetting and drying) would have limited potential to reduce water inputs in California rice production (0.7–2.7 cm season-1). Furthermore, using the most conservative (largest) estimates for each component of the water balance, we conclude that the average water requirement for California rice fields is approximately 108 cm season-1.

中文翻译：

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渗透对水种水稻系统中水平衡的贡献

摘要 水稻 (Oryza sativa) 是所有作物中应用水足迹最高的作物之一，这在许多情况下是由于淹水稻田的高渗透率和侧渗率。更好地了解这些地下水流量的大小和变化及其对稻田水平衡的贡献，对于减少水稻生产的水足迹和限制污染物向地表水和地下水的迁移至关重要。在八个直接播种的加利福尼亚稻田中直接测量了渗透，这些稻田的粘土含量从 20% 到 61% 不等，并且为其中三个田地开发了完整的水平衡。对于后面这些场，直接测量的渗透率与用达西定律计算的渗透率进行了比较，将作为水平衡残差计算的渗透和侧向渗流与直接测量值进行比较。在八个田地中，生长季节的累积渗透范围为 0.04 到 6.95 厘米季节-1。三个水平衡场的平均累积渗流根据直接测量为 2.1 厘米，而根据达西定律计算为 3.2 厘米。结合渗流和横向渗流计算为三个领域的水平衡的剩余项为 17.1 厘米，而根据直接测量为 4.4 厘米，分别对应于水输入的 13.2% 和 3.4%（输入为 98-99%来自灌溉）。基于这些结果，去除洪水的水管理策略（例如 交替润湿和干燥）减少加利福尼亚水稻生产（0.7-2.7 厘米第 1 季）的水投入的潜力有限。此外，对水平衡的每个组成部分使用最保守（最大）的估计，我们得出结论，加利福尼亚稻田的平均需水量约为 108 厘米第 1 季。