中文摘要：

[目的]水分是黄土高原地区植被恢复与农林产业持续发展的主要限制因子,通过对半湿润长武塬区苹果经济林的蒸散研究,掌握苹果林生长季的蒸散耗水规律,为区域性苹果经济林的科学管理及充分挖掘苹果林的生产潜力提供依据。[方法]运用水量平衡法于2012—2014年生长季期间（4月15日—10月15日）对苹果园进行蒸散量估算。其中,降水量由自动气象站实时观测,并结合人工观测数据,保证降水数据的连续性;同时,于每月15日和30日利用中子仪（CNC503B）监测0~6 m特定土层的土壤贮水量,其中0~100 cm阶段土层按每10 cm记录读数1次,100~600 cm土层按每20 cm记录读数1次,并利用土钻法进行校准。[结果]盛果期苹果园在生长季内蒸散量呈明显的双峰曲线,第一峰值出现在7月后半月或者8月前半月,第二峰值出现在9月前半月;2012,2013和2014年苹果生长季内的蒸散量占降水量的比例分别为103%,104%与99%;2012年的蒸散量高出降水量12.1 mm,2013年的蒸散量高出降水量18.2 mm,2014年的蒸散量小于降水量1.2 mm;苹果园蒸散量在生长季内的变异系数为1.0左右。[结论]在属于典型雨养农业区的长武塬区,自然降水是苹果经济林生态系统蒸散耗水的主要水分来源,降水量的多少直接影响着苹果的质量与数量。在枯水年（2012年）和偏枯的平水年（2013年）,蒸散量大于降水量,即降水输入不能满足果园蒸散需水,土壤贮水表现为亏缺状态;在平水年（2014年）,当年降水量可以满足果园蒸散耗水的要求。黄土塬区苹果园土壤水及蒸散对降雨产生快速水文响应机制,降落到林地的雨水迅速以土壤蒸发、植被蒸腾等形式进行水分输出。

英文摘要：

[Objective]Water is the main factor limiting vegetation restoration and sustainable development of agriculture and forestry in Loess Tableland. The main purpose of this study was to investigate the evapotranspiration of an apple orchard in the growth cycle,in order to provide a theoretical basis for scientific management of regional apple orchards and the improvement of potential productivity. [Method]Water balance method was used to calculate the evapotranspiration of a young apple orchard in the Loess Tableland during growing season（ from Mid-April to Mid-October） in 2012- 2014.Rainfall was recorded in real time by automatic weather station in real time and calibrated in combination with manual observation to ensure the continuity of rainfall data. The water storage capacity of soil in a profile of 6 m was measured using a neutron probe（ CNC503B） on the 15^ th and 30^th day of each month,for the 0- 100 cm soil layer,the readings were recorded by every 10 cm,and for the 100- 600 cm soil layer,the readings were recorded by every 20 cm. Then the soil water storage was calibrated with soil-auger-drilling method. [Result ]The evapotranspiration of the apple orchard showed an obvious bimodal curve,with first peak in the second half of July or the first half of August,and the second peak in the first half of September; The evapotranspiration accounted for 103%,104% and 103% of the total rainfall during the growing seasons in 2012- 2014,respectively. In addition,the evapotranspiration of the young apple orchard was12. 1 mm greater than rainfall in 2012,18. 2 mm greater in 2013,but 1. 2 mm lower in 2014. The variation coefficient of evapotranspiration within a growth cycle was about 1. 0. [Conclusion]The loess tableland is a typical rain-fed agricultural area,where the water for evapotranspiration mainly comes from natural rainfall. Thus,the amount of rainfall could directly affect the quality and quantity of the production of apple orchard. In dry（ 2012） and relatively dry（ 2013） years,as the evapotrans