| The area of saline soil in China is about 34.6 million hectares.Due to the poorly rainfall and large evaporation,nearly one-fifth of,7.6 million hectares,arable land are salinized from tropical to cold temperate zone,from coastal to inland,from humid regions to extremely arid desert regions.However,the safety and rational use of soil resources are key elements to improve the quality of cultivated land and to build the best terrestrial ecosystem structure.Saline-alkali land management and water-saving irrigation in saline-alkali land are important measures for the country to store grain in the soil and store grain on the technology,so as well are important guarantee for national food security and ecological security.Therefore,seeking a planting technique based on the principle of water-saving and salt-controlling to reduce the level of soil salinization,enhance soil fertility,and improve the economic benefits of farmland is an urgent problem during the century.To this end,this article is through the combination of experimental method and model simulation,the mechanism of soil water and salt transport in sand cavern structure and the response mechanism of crop roots are studied,and a new method and concept of saving water resources and improving the utilization of salinized farmland are proposed to provide theoretical basis on the field management.(1)Through the two-dimensional artificial soil construction of heterogeneous sand cavern,the article investigate the migration process of the wet front of homogeneous soil and heterogeneous soil under different irrigation treatments.Find the accumulation of soil water and salt in each treatment after redistribution,and fitted each other using the Kostiakov infiltration formula in Origin9.0.The results showed that the homogeneous soil infiltration process conforms to the Kostiakov infiltration formula,and the fitting coefficient is larger than 0.99;The soil salinity is mainly concentrated at a depth of 10-15cm,and the leaching depth is not enough.The heterogeneous soil structure of the sand cavern can significantly expand the soil wet volume,and the irrigation salinity is positively correlated with the wet volume.However,too much irrigation salinity leads to the salt accumulate in the cross-sectional area of the soil and the surface of the soil.Therefore,2g/L irrigation water concentration is recommended for the soil leaching,and the salt washing depth can reach to 20cm.(2)Through the two-dimensional homogeneous soil with tomato planting experiment,the temperature difference was used to construct the dimensional difference of the tomato root system,the mechanism of the root system dimension and the soil water and salt in the root zone was explored,and the conceptual model and hypothesis of the "water-salt-root system" correlation were proposed.The deeper the root system is,the less radiation zone effected by the high salinity in the surface soil;The larger the root system dimension,the lower the soil salt concentration in the root zone.The relatively larger root dimension is conducive to the formation of an alternate mode of action between the water absorption zone and the leaching zone,which provides the possibility of ensuring the healthy root growth.(3)Through the tomato planting experiment of artificially three-dimensional heterogeneous soil structure of the sand cavern,the law of water and salt transport in the soil of the sand cavern structure and the crop response mechanism are studied.Compared with fresh water treatment,brackish water irrigation will form a low-salt zone in the soil,which has a significant effect on salty washing and can increase crop evapotranspiration by 9.54%.In the entire soil profile,the soil moisture at the same depth is in a dynamic equilibrium state,which can independently adjust the root system's moisture demand.(4)The pressure film instrument is used to study the influence of the eight major ions on the soil moisture characteristic curves of sandy soil and clay loam under different treatments,and the measured values are fitted with RETC software.Increasing the ion concentration of the soaking solution can significantly reduce the volumetric water content of the soil and increase the water permeability of the soil;However,the low-concentration ion solution has no significant effect on increasing the volumetric water content of clay loam soil treated with brackish water.In addition,Mg2+can increasing the water retention capacity in sandy soil.Positice ions solution in 2%concentration can increase the water permeability in the clay loam.(5)Using the Hydrus-2D model to simulate the changing process of soil water content and salt content over time in the heterogeneous two-dimensional soil structure of sand cavern monitored by the water and salt sensor,finding suitable soil hydrodynamic characteristic parameters,and using the simulated values to compare with the standard deviation o(?)ne measured value and the correlation coefficient verify the rationality of the model,The simulation result is relatively reliable.To sum up,based on the physical differences in particle gradation,porosity,hydrophilicity,and water conductivity between different soil textures,the self-regulation mechanism of different texture soils to the water and salt movement process and the effect of crop root structure on the soil response mechanism of water and salt transport are researched.Through the artificial construction of the heterogeneous sand cavern in the two-dimensional and three-dimensional soil structure,the positive effect of the sand cavern structure on improving the water and salt migration and accumulation characteristics of saline-alkali soil was discussed from the perspective of soil and crop dual factors.The results show that using sand cavern heterogeneous soil structure to improve soil water and salt dynamic transport mechanism and crop response mechanism has theoretical and practical significance for the improvement of saline-alkali soil. |
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