Guanzhong Plain is one of the most critical maize production areas in Northwest China. It is essential to study the maize irrigation requirement and improve water use efficiency in this area. There is a lack of knowledge about the evaporation portioning and irrigation requirements of crops grown in this region. Based on evapotranspiration observed in a maize cropland using the eddy covariance (EC) technique during four growing seasons (2013, 2014, 2015, and 2017), the seasonal variation of evapotranspiration components and the crop coefficients (Kc) for summer maize in a dry semi-arid area were determined. Energy partitioning has an obvious seasonal variation during growing seasons. The pattern of evapotranspiration partitioning has a clear seasonal variation with the development of the canopy. The pattern of the ratio of transpiration (T) to evapotranspiration (ET) is consistent with the canopy development. For four growing seasons, on a seasonal basis, the ratios of T to ET and E to ET were comparable. In addition, the locally developed crop coefficients were 0.57, 1.01, and 0.50 for the initial, mid, and late stages, respectively. The single crop coefficient derived from local datasets can provide a good prediction of ET. The Kc values reported in this paper were consistent with previous studies conducted in other regions using EC systems but were generally lower than the Kc values derived from ET data measured by lysimeters, the Bowen Ratio Energy Balance system, and the soil water balance method. This indicates that the variability of the locally developed crop coefficient caused by measurement methods is higher than the variability caused by climate.

中文翻译：

---

干旱半湿润气候条件下玉米蒸散分配及作物系数

关中平原是西北地区最重要的玉米产区之一。研究玉米灌溉需求并提高该地区的水分利用效率至关重要。对该地区种植的作物的蒸发分配和灌溉要求缺乏了解。基于在四个生长季节（2013 年、2014 年、2015 年和 2017 年）使用涡度协方差 (EC) 技术在玉米农田中观察到的蒸发蒸腾量，夏季玉米在干旱地区的蒸散量分量和作物系数 (Kc) 的季节性变化确定了半干旱地区。能量分配在生长季节具有明显的季节性变化。蒸散分配格局随着冠层的发育有明显的季节变化。蒸腾量 (T) 与蒸散量 (ET) 的比率模式与冠层发育一致。对于四个生长季节，在季节性基础上，T 与 ET 和 E 与 ET 的比率具有可比性。此外，当地发展的作物系数在初期、中期和后期分别为 0.57、1.01 和 0.50。来自本地数据集的单一作物系数可以提供良好的 ET 预测。本文报告的 Kc 值与之前在其他地区使用 EC 系统进行的研究一致，但通常低于由蒸渗仪、Bowen 比率能量平衡系统和土壤水分平衡方法测量的 ET 数据得出的 Kc 值。