Effect Of Drip Irrigation In Different Depth On Growth And Water-Use Efficiency Of Young Apple Trees

Drought and water deficiency inhibit the development of apple production in Shanxiprovince. The reduction and fluctuation of apple production in arid area are mainly attributedto the dryness of deep soil layer in orchard. Subsurface drip irrigation is one of the savingwater irrigation modes. When it is designed, the crop growth habit, cultivation system andsoil characteristics should be taken into account. Different crop habits need differentconcrete parameters. Research for subsurface drip irrigation was mainly conducted invegetables, little was known in the fruit trees. One-year-old 'Gale Gala' apple trees graftedonto Malus hupehensis Rehd. were used to research the effects of drip irrigation in differentdepths on plants growth and water-use efficiency. Four treatments were executed: naturaldrought treatment (control), surface drip irrigation, middle (13cm-underground) dripirrigation and deep (26cm-underground) drip irrigation.The main results are as follows:1The growth of young apple trees varied with different irrigation treatments.Comparedwith the natural drought treatment, the surface and middle drip irrigations had a better plantgrown, while the deep drip irrigation had the best plant growth. At the same time, the surfacedrip irrigation had the best photosynthesis and stomatal conductance. What's more,netphotosynthetic rate of plants with the middle and deep irrigations decreased firstly and thenincreased, with the initial fluorescence had just the opposite change, and the maximumconversion efficiency of photosynthesis sharply reduced.2At the end of the experiment, the plants of the middle and deep irrigations had thehigher relative water content and the day's stem flow than the other two treatments. Inversely,the sap flow of surface drip was higher than the others at night. The instantaneous water useefficiency and the irrigation water use efficiency of plants grew in the deep irrigation werethe highest.In the vertical distribution, the soil moisture content of the surface drip irrigationwas high during0to10cm, the middle drip irrigations was high during10to20cm and thedeep drip irrigation was high during20to40cm.The relative water content of leaves was related to the root activity. When the relativewater content of leaves was down to a certain degree, the drought treatment had the highest root vigor during0to10cm layer, while surface irrigation was during10to20cm layer,middle irrigation was during10to20cm layer, deep irrigation was during30to40cm layer.3According to the synthetic judgment of malondialdehyde content of leaves,leave′srelative electric conductivity and leaf antioxidant enzymes activity,the drought stress levelwas as follows:natural drought treatment> deep drip irrigation>middle dripirrigation>surface drip irrigation.Meanwhile,in all the treatments, the oxidative stress of theirrigation position was lower than the other positions on the basis of malondialdehydecontent and electrical conductances of different positions.4. The middle and deep irrigations enhanced photosynthesis, biomass, and water useefficiency of apple trees. Compared with the middle irrigation, the plants treated with deepirrigation suffered more severely drought stress on early stage and the growth was inhibited.We conclude that middle irrigation is the best irrigation mode under our experimentalconditions.