| The Loess Plateau in Northern Shaanxi is one of the best apple growing areas in the world.However,the rainfall in this area is small and the distribution of rainwater is unbalanced during the apple growth period,Therefore,apple trees can not meet the water demand in a specific growth period,which affects the final yield and quality of fruit trees.In order to explore the drip irrigation mode of high quality and high efficiency apple production in loess area,In this study,8-year-old Hanfu apple trees were selected as the research objects,and set up three drip irrigation methods: alternate root divided drip irrigation（ADI）,single tube drip irrigation（UDI） and double tube drip irrigation（BDI）,and three irrigation gradients;high water（W1）,middle water（W2） and low water（W3）.There were 9 treatments in this experiment,and each treatment was repeated three times.The effects of drip irrigation methods and irrigation treatments on soil moisture,physiological growth,yield,quality and water use efficiency of apple trees were studied.The main results are as follows:（1）The results showed that the alternate drip irrigation with different roots under moderate irrigation（W2） could increase the soil moisture content and reduce the water consumption of apple trees.There were significant differences in the effects of different drip irrigation treatments on soil moisture content.When the irrigation amount was the same,the order of average soil moisture content was ADI > UDI > BDI.In the flowering and fruiting period of apple trees in 2019,under W1 irrigation treatment,the average soil moisture content of BDI treatment,ADI treatment and UDI treatment were 15.23%,17.27% and 15.92% respectively.There was an increasing trend between 20-40 cm,and a decreasing trend between 40-60 cm.The soil water content first increased and then decreased with soil depth.ADI treatment significantly increased soil water content,which was higher than BDI treatment and UDI treatment.In 0-100 cm soil layer,ADI-W1 treatment had the highest soil volume water content（18.95%）,which was 6.49% and 13.4% higher than UDI-W1 and BDI-W1,respectively.The order of water consumption was W1 > W2 > W3.The order of water consumption at each growth stage of apple trees under each treatment was fruit expansion stage（stage Ⅲ）> flowering and fruit setting stage（stage Ⅱ）> germination and leaf expansion stage（stage Ⅰ）> fruit maturity stage（stage Ⅳ）.The water consumption of ADI treatment was the smallest,and that of BDI treatment was the largest.The water consumption of BDI-W2 treatment in phase Ⅱ increased by 22.1% in 2019 and 4.2% in 2020 compared with ADI-W2 treatment.（2）The results showed that the alternate drip irrigation with different roots under moderate irrigation（W2） could promote the growth of shoot and leaf area,increase the absorbed root length density and root dry weight density,and significantly improve the net photosynthetic rate and instantaneous water use efficiency.The diameter and length of new shoots and LAI of ADI-W2 treated apple were the largest in the middle and late growth period,Severe water deficit inhibited the growth of apple shoots and leaf areas to a certain extent.Apple roots were mainly distributed in 20-60 cm soil layer,and the absorbed root length density accounted for 66.3% of the total roots in 2019.The root dry weight density of ADI-W2 treatment reached the maximum value of 163.7gm-3 in 40-60 cm soil layer on the north and south sides,and the maximum value of 959.9m/m3 in 40-60 cm soil layer on the north and south sides.With the increase of irrigation amount,the root distribution will move down.At the fruit expansion stage（DAF =80d）,the net photosynthetic rate（Pn）,carboxylation efficiency（CE）and leaf instantaneous water use efficiency（LWUE）of ADI-W2 treatment reached the maximum.Pn,Tr,Gs and CE of apple leaves at 11:00 increased first and then decreased with the increase of DAF.The diurnal variation curve of Pn in apple leaves under different water treatments showed "M" type,and the phenomenon of "midday depression" of Pn in ADI treatment was not obvious.The peak value of LWUE in all treatments except ADI-W2 treatment appeared at 10:00 a.m.,which was delayed by ADI-W2 treatment,and the daily average value of LWUE reached the maximum value(3.22μmol·mmol-1) in all treatments.（3）The results showed that moderate irrigation（W2） could improve the fruit yield and single fruit weight,and significantly improve the physical and chemical quality of fruit.At the same time,this treatment could significantly improve the water use efficiency of fruit trees,while severe deficit irrigation（W3） could improve the water use efficiency of irrigation,but it was not conducive to the formation of yield.There was a significant positive correlation between soil moisture and fruit yield,while there was a significant binary nonlinear relationship between leaf area index,net photosynthetic rate and fruit yield.Under the same drip irrigation,fruit hardness decreased with the increase of irrigation water.ADI treatment significantly increased fruit firmness,ADI and BDI treatment increased fruit shape index,but the effect was not significant.The excellent fruit rate of Apple increased significantly with the increase of irrigation amount.The soluble solids,soluble sugar and vitamin C of ADI were higher than those of BDI and UDI.ADI-W1 and ADI-W2 treatments significantly increased the single fruit weight in these two years.Under the same drip irrigation mode,the order of irrigation water use efficiency was W3 > W2 > W1.The irrigation water use efficiency of ADI-W3 treatment was the highest,which was 46.36kg/m3 and 45.90kg/m3 in 2019 and 2020,respectively.The water use efficiency of ADI treatment was significantly higher than that of the other two drip irrigation modes.The water use efficiency of ADI-W2 treatment reached the maximum in two years,which was 7.12kg/m3 and 8.41kg/m3,respectively It is 8.9% and 15.4% higher than ADI-W1 and ADI-W3 respectively,and 7.0% and 13.0% higher in 2020. |
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