A study on water demand characteristics of apple trees in different growing stages in the Loess Plateau Area

Abstract：【Objective】Accurately determining the water demand and seasonal changes of water demand characteristics of apple trees in each growing stage is an important basis for guiding water-saving irrigation in orchards.【Methods】In this study, the trunk sap flow rates (Js) of sample trees in dry orchard in full productive age was monitored for successive two years by means of thermal dissipation method, and the water consumption intensity of each tree was calculated. Correlation analysises were performed between the Js and the leaf area index (LAI) and the phenological characteristics of apples trees.【Results】The total water consumption of apple trees in 2017 and 2018 was 295.5 and 215.3 mm, respectively, accounting for 88% and 58% of the precipitation in the same period. Specifically, the water consumption of apple trees in fruit expansion stage was the greatest with the proportion of 51% in 2017 and 41% in 2018, of the total transpiration during the entire growing seasons each year. The water consumption in different stages decreased in the order of the fruit ripening stage, fruit formation stage, flowering stage, germination stage, defoliation stage, and the dormancy stage. The seasonal variation in water consumption of the trees was similar to that in precipitation. In the germination stage, the waterconsumption intensity of the trees increased rapidly and reached up to 2.17 mm· d^-1 in the fruit expansion stage. After that, it gradually decreased, and the maximum water consumption intensity in the defoliation stage was 1.19 mm·d^-1 . In the dormancy stage, the sap flow in apple trees ran at lower level. The water consumption in this stage accounted for 5% of the total annual transpiration. The maximum daily transpiration intensity was 0.53 mm·d-1 . The seasonal variation of LAI in apple orchard showed a rapid increase from the early April to the mid May with an average rate of 0.07 (dimensionless) per day and reaching 3.2. After that, however, LAI increased slowly with the rate accounted for only 1% of that in the previous period and up to 3.4 before defoliation. In the mid November, the leaves began to fall rapidly and the LAI dropped nearly to zero within few days in the windy weather.【Conclusion】The water demand of apple trees in different growing stages showed great differences, which was not synchronized with the changes of LAI. It is necessary to carry out precise irrigation based on both water demand and soil moisture in each growing period.