Study On Numerical Simulation And Application Of Water Uptake By Roots Of Mature Walnut Under Drip Irrigation

Aksu region is located in the arid inland area of Northwest China,with precipitation less than 100 mm.The local agriculture mainly depends on groundwater pumping and irrigation,and the limited groundwater exploitation restricts the development of agriculture today.The problem of agricultural water use is more serious.Under the policy of vigorously promoting water-saving agriculture,aiming at the problem of limited irrigation system setting level in field plot experimental research,this paper takes the mature walnut tree in Xinjiang Agricultural University Experimental Station in Aksu region of XinJiang as the research object,and uses hydrous-1d software to carry out numerical simulation research on 128 irrigation system scenarios.The purpose of this study is to provide theoretical basis and scientific guidance for the cultivation and irrigation system of walnut under the condition of drip irrigation.In this experiment,Trime IPH soil moisture meter was used to measure the soil moisture content,Hemiview canopy analysis system was used to monitor the leaf area index,micro lysimeter was used to measure the soil evaporation between walnut trees,meteorological data was measured by small meteorological station,and the root distribution of walnut trees was measured by layered and segmented mining method.On this basis,the drip irrigation system of mature walnut was simulated by hydrous-1d model and irrigation system optimization model.The research contents and achievements of this paper are as follows:(1)Law of soil water movementFor the low water treatment with irrigation quota of 37.5 mm,the irrigation amount is small,the soil water storage layer is in the range of 0-40 cm,and the shallow water storage area is less,which can not meet the soil water supply of less than 60 cm.The amount of water treatment with irrigation quota of 45.0 mm is suitable,the soil water storage layer is in the range of 0-100 cm,and the deep water storage in the range of 0-100 cm is sufficient,which can meet the soil water supply in the range of 0-100 cm.When the irrigation quota is 52.5 mm,the irrigation amount of high water treatment is large,and the soil water storage layer is in the range of 0～120cm,with deep leakage,which results in the waste of irrigation water.In this chapter,through the analysis of wave variation,it is concluded that with the increase of irrigation quota,the active layer of soil water moves up,and the water storage layer moves down.According to the analysis of the change of soil water attenuation,it is found that the initial period(1-4 days)is the most intense,and then gradually weakened with time;under different irrigation quota conditions,the less the irrigation amount is,the more intense the change of soil water loss is,and the greater the value of soil water loss rate is.And on the 8th day after irrigation,the soil moisture content of each soil layer of middle and high water treatment was higher than 60%of the field water holding rate,meeting the normal growth of adult walnut trees.(2)Study on distribution characteristics and distribution function of root systemThe spatial distribution characteristics and distribution functions of the roots of the mature walnut trees mainly show the changes in the horizontal and vertical directions.In the horizontal range of 0-150 cm,the peak biomass of walnut root appeared in the range of 0-30 cm,which was 28 143 mg,accounting for 27%.The density of root length increased first and then decreased with the horizontal distance.The change range of root surface area density was 1.51-2.76 cm2/cm3 and 1.25 cm2/cm3.The trend of root volume density was similar to that of root surface area density.That is to say,the fluctuation range is relatively small between 0.17-0.28 cm3/cm3,and the variation range is 0.11 cm2/cm3.In the range of 120-150 cm,the water absorption volume density of root system also decreased significantly.This area was in the water stress area,so the volume density of root system decreased significantly.The peak value of root volume also appeared in the range of 90-120 cm,which was 2 493.01 cm3,accounting for 25%of the total root surface area density;at this time,the cumulative value of root surface area density reached 85%.The distribution function of root biomass,root length,root surface area and root volume density in horizontal direction shows the distribution law of quadratic function form,which increases first and then decreases with the increase of distance from trunk(x).In the vertical direction the change trend of root biomass is a "single peak curve" that first increases and then decreases.The peak value is distributed in the area of 20-30 cm,accounting for 26%of the total surface area of root system.The variation trend of root length,root surface area and root volume is basically similar,the main distribution area is 0-80 cm,and the peak value appears in the area of 20-30 cm.The distribution function of root biomass,root length,root surface area and root volume density all showed the distribution rule of quadratic function form first increasing and then decreasing with the increase of soil depth(z),and the correlation was significant at the level of P<0.01.(3)Irrigation schedule optimization based on Hydrus-1D modelOn the basis of the high accuracy of the validation of the Hydrus-1D model,the simulation of the Hydrus-1D model is applied.Through the simulation of soil water in the growing period of mature walnut,the amount of deep leakage and water stress of soil water under different irrigation systems can be obtained,and then the optimal irrigation system can be selected.In this study,128 scenarios of irrigation system were designed,and the drip irrigation system of mature walnut in South Xinjiang was further determined under the simulation comparison of field measured data in 2018 and 2019.The limit value is selected to eliminate the impact of rainfall on production and growth in the growth period.There will be some deviation in practical application,but it will not have a negative effect on physiological indicators such as yield,which can guide the drip irrigation of mature walnut in South Xinjiang.After optimization,the drip irrigation system of mature walnut was 35 mm,11 times,9 days,385 mm,50 mm,7 times,14 days and 350 mm.At this time,the sum of water stress and deep leakage is 0.62 mm and 1.75 mm respectively,which shows that the combination of hydrous-1d model can reduce the water loss of farmland to the maximum extent and improve the irrigation utilization efficiency.