| The coastal reclamation area of Jiangsu Province is a region where the groundwater is buried shallowly,and the groundwater can recharge the soil in the aeration zone through the rise of capillary.Groundwater affects the root growth of crops,and then affects the root shoot relationship of crops,photosynthesis of irrigation layer,water use efficiency of crops and crop yield.Shallow groundwater is a potential resource for crops to use through soil water.Too deep groundwater depth will bring drought stress to crops,while too shallow groundwater depth will bring waterlogging stress to crops.Reasonable control of shallow groundwater level plays an important role in high yield of crops.Surface drainage layout can quickly remove farmland water and reduce the buried depth of groundwater with high efficiency.Based on the meteorological data of long series and typical hydrological years,this paper uses DRAINMOD model to simulate and analyze the change of groundwater depth The changes of crop yields of winter wheat and sweet potato under different surface drainage layout arrangements were analyzed by AquaCrop simulation.The research results of this paper are as follows:（1）DRAINMOD model is used to calibrate and verify the groundwater depth by inputting meteorological parameters and soil parameters.RMSE-observations standard deviation ratio（RSR）between simulated and actual values of groundwater depth in regular rate and verification period is 0.4 and 0.54 respectively,Percentage bias（PBIAS）is 1.54%and 4.73%respectively,Correlation coefficient（r）is 0.91 and 0.83 respectively,and Nash-Sutcliffe efficiency coefficient（NSE）is 0.84 and 0.68 respectively.DRAINMOD model can accurately simulate the change of groundwater depth in the study area,and can simulate the effect of different subsurface drainage on farmland waterlogging according to long-series meteorological data.In the sensitivity analysis of DRAINMOD model,the three parameters of impermeable layer depth,soil lateral saturated hydraulic conductivity and soil drainage are the biggest influencing variables of the model.These three parameters are adjusted in the calibration and verification of model simulation.（2）Using aquacrop model,the canopy coverage and biomass of crop growth are calibrated and verified by inputting meteorological parameters,soil parameters and groundwater depth parameters.The simulated and verified RSR of wheat and sweet potato canopy coverage were 0.41 and 0.47 and 0.04 and 0.06,pbias were 1.54%and 2.92%and 1.27%and 4.8%,r were 0.91 and 0.90 and 0.99 and 0.98,NSE were 0.84 and 0.86 and 0.98 and 0.95,respectively.The simulated and actual RSR of biomass calibration and verification of wheat and sweet potato were 0.54 and 0.59 and 0.21 and 0.16,pbias were 4.73%and 6.21%and 15.01%and 10.74%,r were 0.83 and 0.81 and 0.98 and 0.99,NSE were 0.84 and 0.86 and 0.95 and 0.97,respectively.Aquacrop model can accurately simulate the yield and growth of winter wheat and sweet potato in the study area.The most effective root depth and anaerobic point of crop parameters,the permeability coefficient of soil parameters and the moisture content of physical properties are the main sensitive parameters of aquacrop model.Among them,soil physical properties are the most sensitive.（3）Based on the simulation results of long-series meteorological data,the layout of subsurface drainage that meets the 85%guarantee rate of waterlogging reduction of high standard farmland in Jiangsu Province is as follows:the guarantee rate of more than 85%can be achieved when the distance between subsurface drainage in the field is less than 20m;When the distance between subsurface drainage is increased to 25m,the buried depth of subsurface drainage shall be arranged below 100cm;When the distance between subsurface drainage is increased to 30m,the buried depth of subsurface drainage shall be arranged at 120cm;From the results of yield analysis,the subsurface drainage arrangement with buried depth of 1.5m and spacing of 20m can reach the highest yield in wheat planting period.More factors are considered in the simulation of sweet potato than wheat,mainly because drought stress accounts for a large part.Through analysis,research and comparison,the subsurface drainage of d150120 can ensure the maximum output.（4）The model simulation found that under the soil conditions in the study area,the groundwater buried depth less than 2.2 m during wheat planting will bring drought stress to winter wheat.When the groundwater depth is less than 1.8 m during potato planting,it will bring drought stress to sweet potato.In this study,when the groundwater depth is less than 1.2 m for a long time,crops will begin to be subjected to waterlogging stress. |
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