Upland fields converted from paddy fields often have a hardpan layer that can cause excessive wet and dry conditions. In this study, the water stress affected by this hardpan was evaluated. Data were obtained from a converted maize field that was divided into plots with and without hardpan. A soil-water-atmosphere-plant (SWAP) model was used to estimate the water stress conditions, such as the reduction in the daily transpiration rate and the vertical distribution of reduction in root water uptake for both plots. When hardpan was present, stress due to wet and dry conditions was more intense in the layer above the hardpan, and dry condition persisted after the hardpan dried. Without hardpan, the wet stress decreased more quickly than when the hardpan was present. The vertical distributions of reduction in root water uptake revealed that dry and wet conditions occasionally occurred at the same time in both plots. In this situation, without hardpan, the shallow layer dried and the deeper layer was wet. With hardpan, the same condition occurred, or the hardpan dried and other shallower and deeper layers were wet. It was considered that the latter condition was a unique characteristic of plots with hardpan—converted fields. The vertical distributions of reduction in root water uptake with the SWAP model can be used as an index to examine the relationship between water stress and tillage practices.

由稻田改建而成的旱地通常有一层硬土层，会导致过度潮湿和干燥的条件。在这项研究中，评估了受该硬质板影响的水分压力。数据是从转化的玉米田中获得的，该田被分为有和没有硬盘的地块。土壤-水-大气-植物 (SWAP) 模型用于估计水分胁迫条件，例如两个地块的每日蒸腾速率减少和根系吸水量减少的垂直分布。当存在硬质板时，由于湿和干条件导致的应力在硬质板上方的层中更为强烈，并且在硬质板干燥后干燥条件持续存在。没有硬板时，湿应力比存在硬板时下降得更快。根系吸水量减少的垂直分布表明，两个地块中偶尔会同时出现干湿条件。在这种情况下，没有硬板，浅层干燥，深层湿润。对于硬质板，发生了相同的情况，或者硬质板干燥而其他更浅和更深的层是湿的。后一种情况被认为是具有硬板转换地块的地块的独特特征。SWAP 模型根系吸水量减少的垂直分布可用作检查水分压力与耕作方法之间关系的指标。或者硬盘干了，其他更浅和更深的层是湿的。后一种情况被认为是具有硬板转换地块的地块的独特特征。SWAP 模型根系吸水量减少的垂直分布可用作检查水分压力与耕作方法之间关系的指标。或者硬盘干了，其他更浅和更深的层是湿的。后一种情况被认为是具有硬板转换地块的地块的独特特征。SWAP 模型根系吸水量减少的垂直分布可用作检查水分压力与耕作方法之间关系的指标。