| The hilly areas in North China are the main areas of Apple planting,and the scale of orchards is expanding,at the same time,the main problem faced by farmers is the shortage of the water resources,the extensive irrigation methods have greatly hindered the quality and high yield of apples.In this paper,the field experiments were carried out on the dwarf red Fuji 3-years-old apple trees to explore the suitable pit depths as well as reasonable upper and lower limits of irrigation,analysis the response relationships between roots,morphological and physiological characters,indexes on photosynthetic characteristics and pit depths as well as reasonable upper and lower limits of irrigation.Meanwhile,the logistic growth model of each index was established at the same time,and discussed the influence of the pit depth and the irrigation of each parameters in the model equations.Finally,each treatment has been evaluated by Principal Component Analysis（PCA）.By this way,evaluating indicator system about pit depths and reasonable upper and lower limits of irrigation was formulated which is based on young apple tree.The main conclusions of this paper are as follows:1.Study on dynamic changes law of soil moisture in different treatments under water storage pit irrigation（1）The soil water content in the water storage pit irrigation increased at first and then decreased in the vertical direction.The soil water content highvalue area treated with water storage pit irrigation obviously decreased with the increase of pit depth,and became wider with the increase of the upper and lower limits of irrigation.The depth of soil water content maximum is two times of the depth of the corresponding pit.The soil water distribution was affected by pit depth,and the upper and lower limits of irrigation affected soil moisture content,and the two factors affect the soil moisture content together.（2）Under the condition of water storage pit irrigation,the average moisture of planned moist layer decreased with the increase of pit depth and irrigation,and the maximum decrease was surface irrigation treatment.2.Regulation of roots growth of different treatments under water storage pit irrigationThe root length,density and total root volume of young apple trees increased first and then decreased trend in the whole growth period.The root length density and total root volume under treatment of the upper and lower limits of irrigation range from 60%θ田to 90%θ田were both better than those of other two irrigation range treatments（from 50%θ田to 80%θ田,from 70%θ田to100%θ田）,the root distribution and soil water distribution of 40 cm pit depth were more match than 60 cm pit depth,simultaneously,the treatment of 40 cm pit depth can induce root growth deeper than the treatment of 20 cm pit depth.The water storage pit depth 40 cm reduce the influence of drought on the surface to the apple trees,promote the cultivation of drought-resistant variety.3.Regulation of morphological and physiological characters of different treatment under water storage pit irrigation（1）The new branches and trunk diameter of young apple trees all showed "S" type during the whole growth period.The accumulative growth of new branches was largest when the pit depth 40 cm and upper and lower limits of irrigation range from 60%θ田to 90%θ田;the accumulative growth of trunk diameter decreased with the increase of pit depth,and increased with theincrease of upper and lower limits of irrigation,and the growth of tree trunk was more sensitive to irrigation.The Logistic growth model can accurately simulate the monthly variation of the accumulative growth of new branches and trunk diameter of young apple trees,and the model was highly fitted.（2）The leaf water potential was closely related to soil water content,and the leaf water potential of surface irrigation was lower than that of water storage pit irrigation.Under water storage pit irrigation,the leaf water potential increases with the pit depth and the upper and lower limits of irrigation;the daily variation of leaf water potential was minimum at the pit depth of 40 cm,and the upper and lower limits of irrigation range from 70%θ田to 100%θ田.4.Regulation of indexes on photosynthetic characteristics of different treatment under water storage pit irrigation（1）The difference in the photosynthetic characteristics of young trees were obviously affected by the solar radiation intensity,rainfall,temperature and other external influences,overall water storage pit irrigation was better than surface irrigation.It has the strongest photosynthetic active radiation under the treatment of 60 cm depth pit and upper and lower limits of irrigation ranger from70%θ田to 100%θ田;stomata conductance and CO2 density intercellular indexes were significantly better than those of the other two irrigation treatments at the upper and lower limits of irrigation range from 60%θ田to 90%θ田,and both of the two indexes were increased with the increase of pit depth;transpiration rate and net photosynthetic rate got the peak value under the treatment of upper and lower limits of irrigation range from 70%θ田to 100%θ田.（2）During the whole growth period of young apple tree,leaf water use efficiency decreases firstly and increases again.The leaf water use efficiency decreased with the increase of pit depth and the upper and lower limits of irrigation.During the whole growth period of young apple tree,leaf light use efficiency of leaves was gradually increasing,then decreased rapidly,and thenincreased gradually.The leaf light use efficiency of leaves decreased with the deepening of pit depth,and increased with the increase of the upper and lower limits of irrigation.As a whole,the leaf water use efficiency and light energy use efficiency of the water storage pit irrigation were higher than those of surface irrigation.Combining with the above theoretical analysis as well as using principal component analysis method（PCA）,under condition of loam soil and arid and semi-arid continental climate in North China,the treatment of water storage pit irrigation which is suit for close planting dwarf srock red Fuji 3-years-old apple trees is 40 cm depth pit as well as upper and lower limits of irrigation range from60%θ田to 90%θ田. |
