Conducting field experiments to determine an optimal strategy for managing water consumption in paddy fields is quite time-consuming and expensive. This study applied HYDRUS-2D model to simulate fluctuations in water level and nitrate transfer over the 2 years of 2013 and 2014 at Rice Research Institute of Iran (Rasht). To monitor water-level fluctuations, a piezometer was installed in the plot. Three irrigation management regimes were considered: first, permanent water flooding or irrigating by as much as 1.3 times the amount of evaporation from the evaporation pan (I 1 ); second, applying irrigation treatment by one time the amount of evaporation from the evaporation pan (I 2 ); third, irrigating by 0.7 times the amount of evaporation from the evaporation pan (I 3 ) from the transplanting date to the end of irrigation period (10 days before harvest). Two fertilizing treatments were considered, i.e., C1 = 60 kg N ha −1 and C2 = 60 kg N ha −1 + 5000 kg compost ha −1 equal to 160 kg N ha −1 . After model run, observed and simulated values were compared using EF (efficiency factor), RMSE (root-mean-squared error), and nRMSE (normalized root-mean-squared error) indices. The results of EF, RMSE, and nRMSE with respect to water-level changes at the calibration stage were 0.94, 5.39 cm, and 7.6%, respectively. At the validation stage, the results of EF, RMSE, and nRMSE were 0.96, 2.25 cm, and 3.2%, respectively. The nRMSE index showed the model's excellent performance in simulating water-level changes. In the case of nitrate transfer, at the calibration stage, the EF values at the two fertilizer levels of C1 and C2 were 0.60 and 0.85, and nRMSE values were 27 and 9.97%, respectively. At the validation stage, the EF values at the two levels of C1 and C2 were 0.60 and 0.99, and nRMSE values were 13.7 and 1.3%, respectively. Based on the values of nRMSE index, the performance of the model in simulating nitrate transfer was shown to vary in the medium-to-excellent class. Overall, the simulation results showed that the HYDRUS-2D model exhibited an appropriate ability to simulate water movement and nitrate transport either from chemical or compost sources; therefore, it can be used for irrigation and fertilizer management in the case of paddy fields to analyze different scenarios.

中文翻译：

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HYDRUS-2D模型在不同灌溉和氮肥施用管理下水稻栽培中的水流和硝酸盐转移模拟

进行田间试验以确定管理稻田耗水量的最佳策略非常耗时且成本高昂。本研究应用 HYDRUS-2D 模型来模拟伊朗水稻研究所（Rasht）2013 年和 2014 年两年间的水位波动和硝酸盐转移。为了监测水位波动，在地块中安装了一个压力计。考虑了三种灌溉管理制度：首先，永久性水淹或灌溉，其灌溉量是蒸发盘蒸发量的 1.3 倍 (I 1 )；第二，以蒸发盘蒸发量的1倍进行灌溉处理（I 2 ）；三、按0灌溉。从移栽日期到灌溉期结束（收获前10天）蒸发盘（I 3 ）蒸发量的7倍。考虑了两种施肥处理，即C1 = 60 kg N ha -1 和C2 = 60 kg N ha -1 + 5000 kg 堆肥ha -1 等于160 kg N ha -1 。模型运行后，使用 EF（效率因子）、RMSE（均方根误差）和 nRMSE（归一化均方根误差）指数比较观察值和模拟值。在校准阶段，EF、RMSE 和 nRMSE 相对于水位变化的结果分别为 0.94、5.39 cm 和 7.6%。在验证阶段，EF、RMSE 和 nRMSE 的结果分别为 0.96、2.25 cm 和 3.2%。nRMSE 指数显示了该模型在模拟水位变化方面的优异性能。在硝酸盐转移的情况下，在校准阶段，C1和C2两种肥料水平下的EF值分别为0.60和0.85，nRMSE值分别为27%和9.97%。在验证阶段，C1和C2两个水平的EF值分别为0.60和0.99，nRMSE值分别为13.7和1.3%。根据 nRMSE 指数的值，模型在模拟硝酸盐转移方面的性能显示为中等至优秀级别。总体而言，模拟结果表明 HYDRUS-2D 模型表现出适当的能力来模拟来自化学或堆肥来源的水运动和硝酸盐传输；因此，它可以在水田的情况下用于灌溉和肥料管理，以分析不同的场景。和 nRMSE 值分别为 27% 和 9.97%。在验证阶段，C1和C2两个水平的EF值分别为0.60和0.99，nRMSE值分别为13.7和1.3%。根据 nRMSE 指数的值，模型在模拟硝酸盐转移方面的性能显示为中等至优秀级别。总体而言，模拟结果表明 HYDRUS-2D 模型表现出适当的能力来模拟来自化学或堆肥来源的水运动和硝酸盐传输；因此，它可以在水田的情况下用于灌溉和肥料管理，以分析不同的场景。和 nRMSE 值分别为 27% 和 9.97%。在验证阶段，C1和C2两个水平的EF值分别为0.60和0.99，nRMSE值分别为13.7和1.3%。根据 nRMSE 指数的值，模型在模拟硝酸盐转移方面的性能显示为中等至优秀级别。总体而言，模拟结果表明 HYDRUS-2D 模型表现出适当的能力来模拟来自化学或堆肥来源的水运动和硝酸盐传输；因此，它可以在水田的情况下用于灌溉和肥料管理，以分析不同的场景。根据 nRMSE 指数的值，模型在模拟硝酸盐转移方面的性能显示为中等至优秀级别。总体而言，模拟结果表明 HYDRUS-2D 模型表现出适当的能力来模拟来自化学或堆肥来源的水运动和硝酸盐传输；因此，它可以在水田的情况下用于灌溉和肥料管理，以分析不同的场景。根据 nRMSE 指数的值，模型在模拟硝酸盐转移方面的性能显示为中等至优秀级别。总体而言，模拟结果表明 HYDRUS-2D 模型表现出适当的能力来模拟来自化学或堆肥来源的水运动和硝酸盐传输；因此，它可以在水田的情况下用于灌溉和肥料管理，以分析不同的场景。