Effects Of Different Drip Irrigation Rates On Physiological Growth,yield And Quality Of Dwarf Closely Planted Apple Trees

Located on the north rim of the Tarim Basin in Xinjiang,Aksu region is the primary apple producing area in Xinjiang,and also an advantageous apple producing area in China.Despite the year-on-year increase in apple planting area and output,water resources shortage and inefficient irrigation water utilization are the key factors restricting the healthy development of apple industry in the region.In this paper,"Red love"（red apple）planted in 2016 was used as the test material.Set three drip irrigation rates:W1 treatment（the wet area can cover 80%of the main distribution area of Apple Roots,and the 6h irrigation）,W2 treatment（the wet area can cover 100%of the main distribution area of Apple Roots,and the 9h irrigation）,W3 treatment（the wet area can cover 120%of the main distribution area of Apple Roots,and the 12h irrigation）.The dripper flow rate was 10L·h^-1,and flood irrigation（CK）was used as a control to study the effects of different drip irrigations on water consumption rate by transpiration,and flood irrigation（CK）was used as the control.To study the spatial distribution law of soil volume water content of dwarf closely planted apple trees under different drip irrigation.Principal component analysis and grey correlation analysis were taken to comprehensively assess the optimal irrigation amount and frequency suited for apple trees in the study area,which carries great significance for studying water conservation in apple drip irrigation in Aksu region.The results show that:（1）The vertical and radial one-dimensional distribution laws of soil volume water content with different drip irrigation amount one day before and one day after irrigation are the same,showing a change trend of first increasing and then decreasing.The two-dimensional distribution of soil volume and water content is circular in high-value area.The high-value area scope of soil volume and water content gradually expands with the increase of irrigation gradient.Under different drip irrigation,the one-dimensional and two-dimensional distributions of soil volume and water content conform to the exponential model,with soil volume and water content positively correlated with the vertical and radial distances.The average soil volume and water content increase significantly after irrigation,but continually decreases with the prolongation of days.（2）The Sap flow velocity of apple trees presents a single bee-shaped curve and a"ji"-shaped change trend under different drip irrigation,displaying stable variation at night.Sap flow velocity;continually decreases between sunset-1:00 the next day,showing stable variation from 1:00 the next day-before sunrise.With the increase of irrigation gradient,the onset time and peak time of Sap flow velocity;will advance.From June to September,the water consumption of apple trees under different drip irrigation amounts is as follows:W3>W2>W1.Compared with other months,apple trees have much greater water consumption by transpiration in July and August.（3）On the instantaneous time scale,solar radiation,atmospheric temperature and air relative humidity are important meteorological factors that affect the sap flow velocity of apple trees.On the daily scale,solar radiation and atmospheric temperature are the key meteorological factors affecting the sap flow velocity;change of apple trees.With the increase of time scale,there are fewer meteorological factors affecting the sap flow velocity of apple trees,and R~2gradually increases.On the daily scale,the soil volume water content at 30cm and 50cm soil layers has a significant effect on the stem velocity rate of apple trees.（4）The new shoot growth of apple trees gradually increases with the increase of drip irrigation.Appropriate reduction of drip irrigation will help to cap the new shoot growth in advance,inhibit the vigorous growth of branches,and promote the differentiation of flower buds.The average daily growth rates of the horizontal and vertical diameters of apples rapidly increase at first,then steady increase,and finally slowly increase.The horizontal and vertical diameters of apples under different drip irrigation are ranked in descending order as follows:W3>W2>W1（5）With the increase of drip irrigation,the transpiration rate,stomatal conductance,net photosynthetic rate and water use efficiency of apple tree leaves increase first and then decrease,suggesting that appropriate drip irrigation helps to improve the photosynthetic characteristics and water use efficiency of apple leaves.Under too much drip irrigation,the photosynthesis of leaves will not be significantly higher,but there will be an inhibitory effect.The intercellular CO₂concentration increases with the decrease of drip irrigation,and the two are inversely correlated.Compared with the young fruit stage,the transpiration rate,stomatal conductance,net photosynthetic rate and intercellular CO₂concentration are significantly higher in the fruit enlargement stage.（6）Different drip irrigation exert significant effects on fruit quality and yield.Appropriate reduction of drip irrigation can increase the content of soluble solids,total sugar vitamin C and mineral elements（K,Ca,Mg,Fe,Zn,Cu）,and reduce the content of total acid.As drip irrigation increases,fruit shape index,single fruit weight and yield increase.Appropriate drip irrigation（W2 treatment）can increase the irrigation water productivity of apple trees(3.11kg·m^-3),and CK treatment has the smallest irrigation water productivity(1.48 kg·m^-3).（7）Based on principal component analysis and grey correlation analysis,a total of 9 indexes are comprehensively evaluated,including yield,irrigation water productivity,soluble solids,total sugar,total acid,water,vitamin C,net photosynthetic rate,and new growth branch length.It is found that W2 treatment has the highest principal component comprehensive score and grey correlation,meaning that the drip irrigation set by W2 treatment is more suitable for the physiology and growth of apple trees in the study area.By comprehensive analysis,the annual irrigation amount of W2 treatment can save48.12%water compared with conventional flood irrigation.There are a total of 11 times of irrigation in the whole growth period,with annual drip irrigation at 5836.5m~3·hm^-2:flood irrigation(2250m~3·hm^-2/time)for spring irrigation and winter irrigation,and drip irrigation(148.5m~3·hm^-2/time)set by drip irrigation W2 in the other growing seasons.