| Groundwater and irrigation water supply in arid and semi-arid areas is of great significance for soil secondary salinization control and crop growth.Hetao Irrigation District in Inner Mongolia is a typical salinization irrigation area in Northwest China.Due to the perennial irrigation of the Yellow River and the drought climate,the local agricultural production is plagued by soil salinization.Appropriate groundwater depth can improve soil environment and promote crop growth and development.Reasonable irrigation system can regulate soil water and salt conditions and increase water use efficiency and yield of irrigation water.Therefore,seeking reasonable groundwater depth,soil salt content and optimizing irrigation system play an important role in ensuring crop growth in irrigated areas.In this paper,the Jiefangzha irrigation area of Hetao Irrigation District is taken as the research area.The enhanced vegetation index(EVI,Enhanced Vegetation Index)extracted from remote sensing images,the groundwater depth data obtained from field experiments and the soil salinity at different depths are used to construct a two-factor coordinate system.The joint response of groundwater depth and soil salinity to vegetation index is determined,and then the soil salinity and groundwater depth range suitable for crop growth are calculated.Irrigation system optimization is based on the example of maize,under the condition that the existing irrigation quota and irrigation times remain unchanged,the irrigation time and irrigation quota at each stage are adjusted to improve water use efficiency and yield,and the influence of irrigation system adjustment on soil salt content is analyzed.At the same time,leaf area index(LAI,Leaf Area Index)was used as the assimilation variable to conduct assimilation research on SWAP model and remote sensing data by using optimization algorithm,which could realize regional yield monitoring.By modifying the irrigation system in the assimilated model to the optimized irrigation system,the regional yield distribution map after the optimized irrigation system is obtained,and then the applicability of the optimized irrigation system in the region is analyzed,which can provide reference for local adjustment of irrigation system..The main conclusions of this paper are as follows:(1)Through quantitative analysis of the combined effects of ground water depth and soil salt content on vegetation index,the appropriate gr oundwater depth and soil salt content for crops were obtained:1)The g roundwater depth should be controlled within 0.99～2.01 and 1.03～1.54m in May and June of wheat,and the soil salt content should be betwee n 1.0～1.3 and 1.53～2.02g/kg.2)The groundwater depth of corn field in June,July and August should be controlled in the range of 1.56～1.80,1.82～2.0m,1.43～2.31m,and the soil salt content should be 1.24～1.68,1.25～1.55,0.98～1.40g/kg;3)The groundwater depth of sunflower field in July and August should be controlled at 0.75～1.70,1.20～1.61m,and th e soil salt content should be 1.46～1.70,5.55～5.84g/kg.(2)Based on the local sensitivity analysis method,six parameters,TSUMEA,SPAN,EFF,TBASE,CVS and CVO,were more sensitive to LAI and yield of maize simulated by SWAP model.(3)Different vegetation indices were used to perform LAI inversion for each growth period of maize,and data assimilation was carried out between LAI inversion and LAI simulated by SWAP model.The R~2values of LAI after assimilation and LAI measured at jointing stage,heading stage and filling stage were 0.90,0.89 and 0.83,respectively.RMSE were 0.262,0.179 and0.211.The average regional yield after assimilation was 11058.56kg/ha..(4)The irrigation system was optimized by adjusting the irrigation date to June 26,July 20 and August 11,and adjusting the irrigation water quota to32mm,146mm and 100mm at each stage.The optimized irrigation system can increase the yield by 6.3%,the water use efficiency by 6.02%,and the regional average yield of the crop growth model by 4%. |
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