Drought has been a major limiting factor affecting agricultural production in the world. Accurately quantitative analysis of the dynamic changes of evapotranspiration and soil water balance is very important for effectively managing water resources and improving water use efficiency under water scarcity. Soil water balance for perennial forage is more complex than the annuals due to stronger roots and periodic evapotranspiration. The objective was to explore the evapotranspiration characteristics and soil water balance of alfalfa (Medicago sativa L.) grasslands under border irrigation at different stand ages and irrigation treatments. A 3-yr field experiment with a full irrigation and 6 regulated deficit irrigation treatments was conducted, and growth-related indicators, soil evaporation and soil water dynamics were observed regularly. Daily evapotranspiration and soil water balance were computed using a modified dual-Kc model which is able to simulate evaporation and transpiration separately. The results showed that soil water simulated by the model and the measured value were in good agreement, and regression coefficients were higher than 0.6 and close to 1.0 in most cuts. The change trend of root zone water under deficit irrigation at single growth stages was similar to that under full irrigation. Under irrigation, the transpiration was the main water loss of alfalfa grasslands. The daily actual evapotranspiration of alfalfa in the 1st cut was higher than 8.0 mm d⁻¹ and even over 15.0 mm d⁻¹ at the middle and later growth stages. In contrast, in the 2nd and 3rd cut, it was always less than 10.0 mm d⁻¹. The daily actual evapotranspiration decreased significantly and immediately after cutting, and daily actual transpiration was reduced to less than 1.0 mm d⁻¹. The change trend of daily actual evapotranspiration under deficit irrigation at single growth stages was also similar to that under full irrigation. The seasonal evapotranspiration could reach 800 mm and was reduced by deficit irrigation. The average proportion of soil evaporation to total evapotranspiration was 18%. With the decrease of irrigation amount, the evapotranspiration, transpiration and irrigation water compensation decreased, while evaporation remained relatively stable and the ratio of evaporation to evapotranspiration increased. A lower relative evapotranspiration deficit (0.041) was obtained under moderate deficit irrigation at the budding stage than those in other deficit cases (0.086 or over). In conclusion, in the arid and semi-arid areas, deficit irrigation could be applied to alfalfa grassland at the budding stage in alfalfa production.

干旱一直是影响世界农业生产的主要限制因素。准确定量分析蒸散量和土壤水平衡的动态变化对于有效管理水资源和提高缺水条件下的用水效率具有重要意义。由于更强的根和周期性的蒸散作用，多年生草料的土壤水分平衡比一年生草料更复杂。目的是探讨紫花苜蓿（Medicago sativaL.) 不同林龄和灌溉处理的边境灌溉下的草原。进行了为期3年的全灌和6次调亏灌溉处理的田间试验，定期观察生长相关指标、土壤蒸发和土壤水分动态。每日蒸散量和土壤水分平衡使用改进的双 Kc 模型计算，该模型能够分别模拟蒸发和蒸腾。结果表明，模型模拟的土壤水分与实测值吻合较好，回归系数均大于0.6，大部分切面接近1.0。单生育期亏缺灌溉下根区水分变化趋势与全灌下相似。在灌溉条件下，蒸腾作用是苜蓿草地失水的主要方式。^-1甚至超过 15.0 mm d ^-1在生长中期和后期。相比之下，在第 2 次和第 3 次切割中，它总是小于 10.0 mm d ^-1。日实际蒸腾量在切割后立即显着下降，日实际蒸腾量减少到小于1.0 mm  d ^-1. 单生育期亏缺灌溉下日实际蒸散量的变化趋势也与全灌下相似。季节性蒸散量可达 800 毫米，并因亏缺灌溉而减少。土壤蒸发量占总蒸发量的平均比例为 18%。随着灌溉量的减少，蒸散量、蒸腾量和灌溉水补偿量均减少，而蒸发量保持相对稳定，蒸发量与蒸散量的比值增加。在萌芽阶段适度亏缺灌溉下获得的相对蒸散量亏缺 (0.041) 比其他亏缺情况下 (0.086 或以上) 低。总之，在干旱和半干旱地区，