Study on the growth, water consumption and yield of drip-irrigated apple trees with dwarfing rootstock and close planting in South Xinjiang

Abstract:【Objective】In southern Xinjiang, evaporation is strong and rainfall is scarce. Water resource is extremely limited. This study was carried out in order to improve water use efficiency and develop high-yield and efficient water management programs.【Methods】In this experiment, 5-year-old densely planted Royal Gala trees on dwarfing rootstock were used as the experimental materials in 2019—2020 in Alar, southern Xinjiang. Five irrigation volumes were set: W1 (13.5 mm), W2 (18 mm), W3(22.5 mm),W4 (27 mm) and W5 (31.5 mm). ET0-P was used to guide irrigation. Irrigation was triggered at the same time in the five irrigation treatments when ET0-P reached 22.5 mm. The study examined the influences of different irrigation volumes on apple growth, water consumption during growth period, yield and wa-ter use efficiency, and to provide reference for the large-scale production of apples on dwarfing root-stocks in densely planted orchards in southern Xinjiang.【Results】New shoots grew rapidly initially and but slowly later, and the length of new shoots increased significantly with the increase in irrigation vol-ume. There was a significant difference in water consumption between different irrigation treatments(p ＜ 0.05). The W1 treatment had the lowest water consumption, which was 304.21 mm and 349.01mm in 2019 and 2020, respectively, and the W5 treatment had the highest water consumption, which  was 692.28 mm and 746.94 mm in 2019 and 2020, respectively. Water consumption rate increased first and then decreased during the growth period. It reached the highest value during the fruit expansion pe-riod. The water consumption in W5 treatment reached 511.72-542.89 mm in fruit expansion period, fol-lowed by the fruit maturity period, which was 119.68-131.45 mm, and the lowest in flowering and fruit-setting period, which was 60.88-72.60 mm. The variations in water consumption modulus coefficient and water consumption intensity were consistent with water consumption. In 2019 and 2020, the water consumption modulus and water consumption intensity during fruit expansion period in W5 treatment were 0.73-0.74 and 6.73-7.24 mm · d- 1, respectively, and the water consumption modulus coefficient and water consumption intensity during the fruit setting period were 0.09-0.10 and 4.54-4.68 mm·d-1,respectively. The crop coefficient increased with the increase in irrigation volume, and the crop coeffi-cient during the whole growth period was the largest in W5 treatment and lowest in W1 treatment in both seasons. Crop coefficient showed a single-peak curve during the whole growth period, peaking in the fruit expansion period. The value in W5 treatment was 1.36 and 1.49 while that in W1 treatment was 0.59 and 0.68 in 2019 and 2020, respectively. Apple yield increased first and then decreased with the in-crease in irrigation volume. The yield in W4 treatment was the largest, which was 26 960 kg · hm-2 and 35 328 kg·hm-2 in 2019 and 2020, respectively, not significantly different from W3 treatment, but signifi- cantly higher than the other treatments. The water use efficiency in W1 and W3 treatments was larger,and the two-year average values were 6.59 kg·m-3 and 6.46 kg·m-3, respectively. There was no signifi-cant difference in water use efficiency among W1, W2, W3 and W4 treatments in 2019, but they were sig- nificantly higher than W5 treatment. The result in 2020 was consistent with that in 2019, but there were significant differences among the treatments. Irrigation water use efficiency displayed a similar pattern with water use efficiency. However, in 2019, there was no significant difference between W1 and W3 treatments, and between W2 and W4 treatments, and in 2020, there was significant difference between W2 and W4 treatments. At the same time, it could be seen from the regression that the correlation coeffi- cients between the average value of output in each treatment, water use efficiency, and irrigation water use efficiency and the irrigation volume in 2019 and 2020 were 0.80, 0.66, and 0.70, respectively, and both water use efficiency and irrigation water use efficiency decreased with the increase in irrigation volume. The fitting curve of irrigation water use efficiency, water use efficiency, yield and irrigation vol-ume correspond to an irrigation volume of about 460 mm.【Conclusion】Comprehensive analysis of ap-ple growth, water consumption, yield and water use efficiency showed that the irrigation volume during the growth period was 22.5 mm, and the irrigation frequency was 21 times, which was a suitable irriga-tion mode for dense apple planted on dwarfing rootstocks in South Xinjiang.