水分利用效率（WUE）是农田生态系统碳水循环的重要指标，对指导农业灌溉和提高水分生产力有重要意义。宁夏灌区是我国地处干旱气候带的大型灌区，其中，玉米种植面积最大。在涡度通量观测农田生态系统实际蒸散发（ET）的基础上，利用氢氧稳定同位素法将蒸散发分割为土壤蒸发（evaporation，E）、植物蒸腾（transpiration，T），并通过光能利用模型估算宁夏引黄灌区典型玉米农田生态系统的总初级生产力（GPP），计算群体水分利用效率WUE_T=GPP/T、生态系统水分利用效率WUE_ET=GPP/ET以及固有水分利用效率（Intrinsic Water Use Efficiency）IWUE_VPD=（GPP·VPD）/ET三种水分利用效率，进而从函数响应关系、相关性以及敏感性三个方面分析不同水分利用效率与气温、饱和水汽压差（VPD）、CO₂浓度、光合有效辐射以及土壤含水量等环境因子之间的关系。结果表明：宁夏引黄灌区玉米农田生态系统生长季的实际蒸散发变化呈单驼峰型，作物蒸腾与实际蒸散发的变化趋势相一致。WUE_T在生育期内呈“W型”变化，WUE_ET与IWUE_VPD在生育期内呈“单峰型”变化，三种WUE的峰值出现在抽雄期，分别达到5.90 kg C·m^-3·H₂O、5.02 kg C·m^-3·H₂O和32.90 kg C·hPa·m^-3·H₂O，灌浆后期三种水分利用效率开始降低，玉米成熟晚期由于蒸腾微弱所以WUE_T略有增加。WUE_T、WUE_ET和IWUE_VPD与土壤含水量显著正相关，相关度和敏感性最强；VPD与三种WUE显著负相关，相关度和敏感性最强次之；气温、光合有效辐射以及CO₂浓度与三种WUE的负相关性但不是敏感因素。因此，在宁夏引黄灌区土壤水分和VPD是影响玉米农田生态系统WUE的关键因素。

Water use efficiency (WUE) is an important indicator of the carbon-water cycle of farmland ecosystems and is of great significance for guiding agricultural irrigation and improving water productivity. Ningxia Irrigation area is a large-scale irrigation district located in the arid climate zone of China, where the corn planting area is the largest. Based on eddy flux observation of actual evapotranspiration (ET) of farmland ecosystems, this paper used the hydrogen and oxygen stable isotope method to segment evapotranspiration and estimated the total primary productivity (GPP) of typical maize farmland ecosystems in the Yellow River irrigation area of Ningxia using the LUE (Light Use Efficiency) model. Population Water Use Efficiency WUE_T = GPP/T, Ecosystem Water Use Efficiency WUE_ET = GPP/T, and Intrinsic Water Use Efficiency IWUE_VPD = (GPP·VPD)/ET were calculated. Then, the relationship between different WUE and environmental factors, such as air temperature, saturated water vapor pressure difference, CO₂ concentration, effective photosynthetic radiation, and soil water content was analyzed from three aspects: functional response relationship, correlation, and sensitivity. The result showed that the variation of actual evapotranspiration in the growing season of the maize agro-ecosystem in the Ningxia yellow irrigation area was single-humped, and the trends of crop transpiration and actual evapotranspiration were consistent. The variation of water use efficiency in the growing season was different among the three species, with WUE_T showing a “W-shaped” variation pattern during the growing season while WUE_ET and IWUE_VPD showed a “single-hump” variation pattern. All three WUE peaks occurred at the male tasseling stage, reaching (5.90 kg C·m^-3·H₂O, 5.02 kg C·m^-3·H₂O, 32.9 kg C·hPa·m^-3·H₂O) respectively. The three kinds of water use efficiency began to decrease in the late filing period, and WUE_T increased slightly in the late ripening period due to weak transpiration. Among the five environmental factors, WUE_T, WUE_ET and IWUE_VPD were positively correlated with soil water content, and the correlation and sensitivity were the strongest. The three water use efficiencies were significantly negatively correlated with VPD, with the second strongest correlation and sensitivity. Air temperature, photosynthetically active radiation, and CO₂ concentration were negatively correlated with the three kinds of WUE but not critical factors. Therefore, soil moisture and VPD are the key factors affecting the WUE of the maize farmland ecosystem in the Yellow River irrigation area of Ningxia.