Abstract: [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 was 12.1 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 evapotranspiration was greater than the rainfall, the water supply from rainfall could not meet the water consumption by apple orchard, resulting in deficit of soil water content. However, in a normal year (2014) with average precipitation the water consumption of young apple orchard can be met. The soil water and evapotranspiration of apple orchard had a rapid hydrological response to rainfall in the loess tableland, and rain water in the apple orchard can be rapidly transformed into evaporation and vegetation transpiration.

Key words: Loess Tableland, apple orchard, water balance, evapotranspiration, precipitation, soil water storage