Study On Regulated Deficit Irrigation System Of Main Fruiting Apple Orchard Based On Soil Water Availability

Southern Xinjiang is located in the extremely arid area of China,where water resources are scarce and unevenly distributed in spatial and temporal distribution.The irrigation method of regional apple orchard is mainly flood irrigation,and the water use efficiency is low.In order to solve this problem,this paper aims to construct a regulated deficit irrigation system suitable for apple orchards in southern Xinjiang and improve water use efficiency.In 2022,the regulated deficit irrigation experiment of apple orchards was carried out in the eleventh company of the fifth regiment of the first division of Xinjiang Production and Construction Corps.Four treatments were set up in the experiment,namely sufficient irrigation（W1）,mild deficit（W2）,moderate deficit（W3）and severe deficit（W4）.Based on soil water availability,the irrigation upper limit of all irrigation treatments is field capacity(θ_fc,unit:cm3 cm-3),that is,the relative water content is 100%.In the experiment,the segmentation point of soil readily available water and difficultly available water was used as the threshold of soil water deficit,that is,the lower limit of irrigation for sufficient irrigation treatment,and the corresponding relative water content was 75%.The wilting coefficient is the soil water content corresponding to the permanent wilting of plants,corresponding to the lower limit of irrigation for severe deficit treatment,and the corresponding relative water content is 45%.Therefore,the relative water content corresponding to the soil water deficit interval is 75%-45%,and the three equal division points correspond to the critical values of mild,moderate and severe soil water deficit,respectively.Therefore,the relative water content corresponding to the lower irrigation limit of mild deficit and moderate deficit treatments is 65%and 45%,respectively.The irrigation soil depth was designed to be 0-60 cm,and the soil water content was monitored in real time.When the soil relative water content was reduced to 75%,65%,55%and45%,W1,W2,W3 and W4treatments began to irrigate respectively.The effects of different irrigation treatments on soil moisture change,water consumption,growth physiology of fruit trees,yield and quality of apple were studied,and the suitable irrigation system was selected.The main results of this study are as follows:（1）Irrigation water is the main source of water consumption of fruit trees.The variation range of soil moisture in 0-60 cm soil layer during the growth period was higher than that in 60-120 cm soil layer.The water absorbed by the roots of fruit tress is mainly concentrated in the 0-60 cm soil layer,and irrigation water is the main source of soil water consumption.The total irrigation amount of W1,W2,W3 and W4treatments was 525.6,424.8,339.6 and 288.6 mm,corresponding to water consumptions of 574.8,477.6,396.6 and 344.4 mm,respectively.（2）Soil water deficit led to the decrease of transpiration rate and photosynthetic rate.Appropriate regulated deficit irrigation can inhibit the growth of branches,increase soluble sugar content,MDA content and POD activity in leaves,increase yield and improve quality.the corresponding apple yields of W1,W2,W3 and W4 treatments were 20707.5,226687.5,18465.0 and 18480.0 kg,respectively.The quality of W2treatment was the best.（3）Based on the indexes of yield,quality,irrigation amount and water use efficiency,the regulated deficit irrigation management mode suitable for the main fruit apple orchard in southern Xinjiang is mild regulated deficit irrigation.The irrigation system is:（1）the irrigation is started when the soil relative water content is reduced to 65%based on the real-time monitoring of soil water content;（2）the calculation formula of irrigation quota（IWQ）is calculated as IWQ mm=0.35×θ_fc×H,where,H=600 mm;（3）and according to the actual situation of irrigation management,without setting a specific number of irrigation.