Study On Simulation Of Soil Water Change And Water Productivity In Apple Orchard Based On EPIC Model

The Loess Plateau is the world’s largest contiguous apple planting area.Apple planting has become an important pillar industry for local economic development.However,the orchard management model in this area is unscientific.In addition,scarce precipitation and strong water consumption for fruit tree growth have led to deep dry farming in the local orchard.The soil water deficit is serious,which seriously affects the sustainable and stable development of the orchard.In this study,different study areas（Fufeng,Changwu,Luochuan,Yan’an,Zichang,Mizhi）were selected from south to north based on the precipitation gradient in the Loess Plateau.On the basis of investigation and fixed-point detection,combined with the Windows-based EPIC model,long-term quantitative simulation of apple production and deep soil moisture changes in different regions of the Loess Plateau,comparison of precipitation in different regions,and evaluation of natural and man-made management factors on orchard yield To determine the appropriate planting density and reasonable water replenishment level for orchards in different regions of the Loess Plateau,and explore the impact of future climate conditions on the yield and soil moisture changes of apple orchards in various regions.It is the soil moisture content of apple orchards in the Loess Plateau.Sustainable utilization and stable development of the apple industry provide scientific basis.The main conclusions of this study are as follows:（1）Through field experiments and investigations,the required parameters for the operation of the apple orchard model in the relevant study area were obtained.The model was calibrated and verified in this study.The EPIC model was used for yield and soil in Fufeng,Changwu,Luochuan,and Yan’an.The simulation accuracy（R²）of the water simulation value is 0.992,0.960,0.982,0.983 and 0.860,0.878,0.860,0.866,respectively,and the simulation accuracy is yield>soil moisture.Although EPIC has high accuracy in the simulation value of yield and soil moisture content in different regions（RRMSE<10%）,the EPIC model only formulates physiological parameters for the crop parameters in the mature period in the process of simulating the growth of apple orchards.There are certain problems in the simulation effects of the juvenile and declining periods of the decay period,and the orchard yields in these two periods are often overestimated.Therefore,in the simulation,you should try to ensure that only the growth period corresponding to the physiological parameters is simulated to ensure the accuracy of the model simulation.（2）According to the simulation results of water productivity and soil moisture changes in apple orchards in different study areas from 1980 to 2020,it is shown that the output of Fufeng,Changwu,Luochuan,and Yan’an apple orchards all increased first and reached the maximum and then fluctuates.Decreasing trend,the annual average yields are 27.52 t·hm^-2,26.75 t·hm^-2,26.41 t·hm^-2,25.81 t·hm^-2,and the average yield is positive with the local multi-year average precipitation.Relevant;drought stress occurred successively in the 21st,18th,18th,and 16th years in the four places respectively.The average annual drought stress days were 13.31,16.37,15.55and 27.08 days,and the deep soil dry layer appeared on the 16th,13th,and 13th respectively.And 8 years;the decrease values of the effective water storage in the deep soil are about 1417.0mm,1468.5 mm,1540.5 mm,and 1573.0mm,respectively,and the declining rates are 64.41mm·a^-1,81.58mm·a^-1,85.58 mm·a^-1,98.31 mm·a^-1,the descending rate is Yan’an>Changwu>Luochuan>Fufeng;as the average annual precipitation level in the study area increases,the time of drought stress in the orchards in each study area increases.Later,the formation period of stable soil dry layer is also delayed correspondingly,and the average annual output of orchard increases,and 18-25 years is the more reasonable utilization interval of orchard soil moisture.（3）In the simulation process,under the condition of increasing precipitation,the output of orchard does not increase continuously.Both low and high precipitation will affect the output of orchard.The suitable precipitation interval is 500～800mm.In this precipitation interval The inner orchard can achieve the best production conditions;under different management measures,the output of the orchards in Fufeng,Changwu,Luochuan,and Yan’an shows different regularities with soil moisture,and high planting density cannot get the best output.As a result,the most suitable planting densities in the four regions were 1143 plants·hm^-2,1000 plants·hm^-2,1000plants·hm^-2 and 833 plants·hm^-2.The change of planting density did not affect the soil moisture of the orchard.The rate of content consumption is relatively consistent with the rate of soil moisture decline under different planting densities,but with the increase of planting density of orchards,the appearance of the dry soil layer of the orchard is earlier;Fufeng,Changwu,Luochuan,and Yan’an are the most common areas.The suitable supplementary irrigation levels are 100mm,150mm,150mm and200mm.With the increase of irrigation water level,the overall soil water consumption rate of orchard differs significantly,but the increase of irrigation water level delays the appearance of dry soil layer,and The impact on the yield of fruit trees in the middle and late stages of growth is more obvious.Orchards with higher irrigation levels have higher yields and higher average annual yields.（4）In the future climate situation,the temperature and precipitation of Fufeng,Changwu,and Yan’an will all increase under the current climate level.The temperature increase range is 0.57～5.66℃,and the precipitation increase level is34.20～80.57mm;The increase in precipitation has a promoting effect on the increase in yield and the delay of soil water consumption;the increase in temperature will cause the decrease in the average yield for many years and the formation of a stable dry layer of soil earlier;the increase in temperature has a greater impact on the temperature The negative impact of high yields is greater than the positive impact of rising precipitation,especially in the current climate conditions where the average temperature is higher and the rainfall is scarce,the yield will be greatly reduced in the future climate scenarios,and the time when the dry soil layer appears Significantly ahead of schedule;in the two scenarios of RCP4.5 and RCP8.5,the increase in precipitation has limited impact on deep soil moisture,because precipitation cannot supplement the consumption of deep soil,but gives fruit trees even more when the temperature rises.Suitable growth conditions,this effect is generally not conducive to the maintenance of high-yield life of fruit trees,especially in drier areas,this negative effect is more obvious.In summary,the calibrated EPIC model can be used to simulate the growth of apple orchards in the Loess Plateau,and the simulation effect is good.Considering comprehensively from the perspectives of increased production,continuous use of soil moisture,and orchard economic benefits,the reasonable use period of fruit trees is 18-25 years,the reasonable planting density is 833-1143 plants·hm^-2,and the water supply should not exceed 800mm·a^-1.