The ‘effective’ root depth of perennial ryegrass used for irrigation scheduling has substantial implications when estimating irrigation requirements. This study included field measurements of 20 percolation lysimeters with diameters and heights of 500 and 900 mm, respectively, installed on the Lincoln University Dairy Farm, Christchurch, New Zealand, to estimate actual evapotranspiration (ET_a) based on water balance analysis for three soil depths: 500, 600 and 700 mm. Reference evapotranspiration (ET_r) was estimated based on the CropWat 8 model. Perennial ryegrass height (h cm) was measured for each lysimeter. Among the three soil depths, 500 mm produced the highest regression coefficient for the crop coefficient (K_c = ET_a/ET_r) and h relationship. The results indicate the need to consider a 500 mm root depth to estimate irrigation requirements on this farm to achieve optimal water productivity. A noticeable fluctuation in daily soil water content for the top 500 mm soil profile, measured in time domain reflectometry probes and with an Aquaflex soil moisture sensor, also reinforces the earlier statement.

中文翻译：

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通过水平衡和土壤水分监测评估灌溉计划的有效牧草根深度

在估算灌溉需求时，用于灌溉计划的多年生黑麦草的“有效”根系深度具有重要意义。这项研究包括对安装在新西兰基督城林肯大学奶牛场的 20 个直径和高度分别为 500 和 900 毫米的渗滤器进行现场测量，以根据三种土壤的水平衡分析估算实际蒸散量 (ET _a )深度：500、600 和 700 毫米。根据 CropWat 8 模型估算参考蒸散量 (ET _{r )。} 测量每个蒸渗仪的多年生黑麦草高度 ( h cm)。在三个土壤深度中，500 mm 产生了最高的作物系数回归系数 ( K _c = ET _a /ET _r ) 和h的关系。结果表明需要考虑 500 毫米的根深来估计该农场的灌溉需求，以实现最佳的水生产力。使用时域反射探头和 Aquaflex 土壤湿度传感器测量的顶部 500 毫米土壤剖面的每日土壤含水量显着波动，也强化了之前的说法。