| Hetao Irrigation Area in Inner Mongolia is located in the middle and upper reaches of the Yellow River,which is one of the largest irrigation areas in China.Agricultural irrigation water accounts for more than 90%of the total water consumption.In this area,surface irrigation has been the main irrigation method for a long time,characterized with low water use efficiency,shallow underground water level and increasingly serious secondary salinization of soil.Therefore,it is of great significance for the sustainable application in Hetao Irrigation Area of Inner Mongolia to fully study and reveal the distribution characteristics and temporal and spatial variation of soil water and salt in this area,seek more efficient water-saving irrigation methods,and put forward relevant irrigation management and control countermeasures.In order to further develop water-saving and efficient irrigation methods and realize the control of agricultural water-saving and salinization,the typical salinized farmland in Hetao irrigation area was selected in this study.The methods of field experiment,statistical analysis and model simulation were used.Three irrigation methods,border irrigation?BI?,furrow irrigation?FI?and drip irrigation?DI?,were set in the field experiment.One irrigation level of border irrigation is implemented according to the local Yellow River water diversion date and traditional irrigation model,and three irrigation levels of high?H?,medium?M?and low?L?are set respectively under furrow irrigation and drip irrigation.The temporal and spatial changes of soil moisture and salinity,the response of spring maize growth and economic benefits under different irrigation methods were comprehensively analyzed.Water and solute transport process model HYDRUS-2D and maize growth model DSSAT-CERES-Maize were used to simulate and predict the soil water and salt transport process under different scenarios and the growth of spring maize under the climate change,so as to put forward the appropriate water-saving strategy and irrigation schedule suggestions.The main contents and conclusions are as follows:?1?The inter-annual variation of soil water and salt under different mulching irrigation methods was analyzed.Through the analysis of soil volume water content change,vertical dynamic change of electrical conductivity,soil water storage and soil salt storage in different engineering treatments of 0?120 cm profile during sowing and harvest,it was found that the reduced degree of soil water content in ridge cropping treatment was less than that in plain cropping treatment,which played a certain effect of water conservation.Ridge cropping also had a good effect on the conductivity of salt suppression.Soil salt in mulching treatment was concentrated in the surface layer,and ridge cropping mulching treatment had obvious effect of water retention and steam suppression,which played a better effect of salt pressing.?2?The movement of soil water and salt under different film mulching irrigation methods was simulated.Compared to drip irrigation and furrow irrigation soil water and salt movement under the condition of simulated values and measured results show that the surface soil moisture and salinity fluctuation is bigger,the effect of area is relatively less volatile,deep soil fluctuates significantly decreases,and the main reason is that the surface soil by soil evaporation and atmospheric temperature fluctuation affected by external environment.Compared with furrow irrigation,drip irrigation performed better in retaining water pressure and salt in root zone.The HYDRUS-2D model is accurate in simulating soil water and salt migration in drip and trench irrigation,which makes up for the shortcomings of field experiments in observing some important times in some regions.?3?The response of crop growth and yield under different mulching irrigation methods was analyzed.On average,10 percent of irrigation water was lost through deep seepage under border irrigation,while under low water conditions for drip irrigation,about 10?29mm of groundwater rose through the capillary to recharge the root zone for crop absorption;Compared with traditional border irrigation,high water treatment with furrow irrigation can increase corn grain yield and net benefit,while medium water treatment can save 31%of irrigation water while maintaining the same yield and net benefit.Under drip irrigation,high and medium water treatment significantly improved spring maize grain yield and net yield and had higher water use efficiency?WUE?under the conditions of 19%and 57%water conservation compared with border irrigation.When water diversion resources are still relatively sufficient,furrow irrigation of 360 mm,or even 450 mm can be selected to achieve similar or slightly higher yields and economic benefits than border irrigation.However,in areas where irrigation water resources are relatively deficient,and the economic conditions and farmers'acceptance are relatively high,it is suggested to choose a more water-saving drip irrigation method,and utilize the intermediate water treatment with the lower limit of soil matrix potential of-30 k Pa to greatly save irrigation water while increasing grain yield and net income.?4?The growth process of maize under different precipitation years was simulated.Through the comparison and analysis of the RMSE of simulated soil moisture and observed between DSSAT-CERES-Maize and HYDRUS-2D,the results showed that there was a big deviation between soil moisture dynamic simulation and observation value by DSSAT-CERES-Maize and HYDRUS-2D.In order to improve the DSSAT-CERES-Maize model to simulate the growth and development process of maize under ridge film mulching,the parameters of DSSAT-CERES-Maize soil module were modified by trial and deviation method,mainly including the root growth parameter SRGF,soil drainage performance parameter SLDR and runoff potential parameter SLRO.It was found that the deviation between the simulated and observed values of maize yield in 2017 and 2018 was reduced,and the relative root mean square error?RMSE?between the simulated and observed values of soil moisture was relatively reduced,and the simulation accuracy was improved.The modified DSSAT-CERES-Maize irrigation method was optimized for different precipitation years in Hetao area.According to the yield and WUE,it can be found that the best irrigation measure was to set the threshold at 10%?the plant available water is lower than 10%?for the three years of high water year,normal water year and drought year.Therefore,based on the modified DSSAT-CERES-Maize model,the optimal irrigation water quantity of maize under ridge mulching and film mulching in Hetao area can be quantified.?5?The growth process of maize under climate change was simulated.In order to optimize the water management measures of spring maize in Hetao area under climate change,meteorological data of 29 climate change scenarios were generated based on Hetao historical meteorological data?1961-2018?,driving DSSAT-CERES-Maize to simulate spring maize yield,WUE and irrigation amount with ARR1-ARR9 irrigation measures under 29 climate change scenarios.The results showed that the yield of maize decreased by211,942,943 and 1262 kg hm-2 under the nine irrigation measures in each scenario only when the temperature increased by 0.5?,1.0?,1.5?and 2.0?.When the temperature increased by 0.5?,WUE decreased by 0.2 kg hm-2 mm-1 under the nine irrigation measures,while the WUE increased by 0.42 kg hm-2 mm-1 under ARR1-ARR9 irrigation measures when the rainfall increased by 5%.Under the condition of temperature and rainfall changing at the same time,the WUE value of all the nine irrigation measures was the smallest,while the WUE value of+2.0?&25%didn't decreased significantly compared with+1.5?&25%,which indicated that temperature and rainfall had interactive effects on WUE,When the irrigation water limit was set at 10%,the water content of spring maize in Hetao area could be optimized by WUE(12.3-27 kg hm-2 m-1)and irrigation amount?286-311 mm?.To sum up,based on three-year field experiment and combined with model tools,the study clarified the soil water and salt transport under different irrigation methods,analyzed and predicted the maize growth,yield and economic benefits under different scenarios,and put forward the appropriate irrigation level of different irrigation methods in Hetao irrigation area.The research results will provide scientific basis for the formulation of water-saving irrigation system and agricultural water and soil resources management in Hetao irrigation area. |
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