Spatiotemporal Variation Of Water And Salt Before And After Improvement Of Saline-alkali Land In Hetao Irrigation District And Improvement Effect

As an important commodity grain producing area in China,soil salinization is a key factor affecting the high quality development of the irrigation area,and the application of comprehensive technology for saline land management is becoming more and more urgent.2018-2020 Wuyuan County launched the implementation of 50,000 mu of"salt and grass improvement(forage)for herding"pilot demonstration project,which is based on The project is based on the"five-in-one"comprehensive improvement measures,supplemented by the construction of farmland water conservancy infrastructure to carry out comprehensive saline land management in the demonstration area,during which several improvement enterprises and units are introduced to carry out experimental demonstrations.In this thesis,we use regional soil-groundwater-surface water information monitoring,classical statistics,geostatistics,spatial interpolation,correlation analysis and other methods to study the spatial and temporal variability of soil water and salt,the effect of saline soil improvement,groundwater dynamics,and soil water-salt balance in the test area under the conditions of integrated saline land improvement.The assessment index system was constructed by combining the Delphi method and traditional statistical methods,and the weights and assessment methods of each index were determined to achieve a comprehensive assessment of the improvement effect of improvement enterprises and experimental units.The research results are as follows:(1)Before improvement,the soil salinity structure ratio of each layer ranged from4.76%to 33.05%,which was subject to the combined effect of structural and stochastic factors,and the spatial variability of surface soil salinity was large;after improvement,the soil salinity structure ratio decreased by 7.28%and the soil organic matter structure ratio decreased by 3.73%,which enhanced the soil structure,reduced the variability of organic matter and salinity,and tended to be homogeneous in spatial distribution,and the analysis concluded that It is mainly due to the implementation of deep pine and rotary tillage measures that broke the soil plow bottom layer and improved the soil structure.The cations in soil salt-based ions are mainly Na⁺and K⁺,accounting for 39.09%of the total ions,and the soil anions are mainly Cl^-and SO₄^2-,accounting for 18.34%and18.56%of the total ions.The soil salts in the test area are mainly sodium salts and sulfates,and the salt ions develop in the direction of homogeneity after improvement.(2)Under the intervention of comprehensive improvement measures,the soil salt phenology in the study area was significantly weakened,the soil in the cultivated layer was desalinated,the soil in the deep layer accumulated salt,and the distribution of soil salts in each layer tended to be even.Before spring tillage,the total soil salinity in the cultivated layer decreased by about 2.67 g/kg in the late improvement period(April 2020)compared with the early improvement period(April 2018),and the total soil salinity in the deep layer of 40-100 cm increased by about 1.60 g/kg,and after autumn harvest,the total soil salinity in the cultivated layer decreased by about 0.801g/kg,and the increase in total soil salinity in the 40-100cm deep layer was about 0.537g/kg.The application of organic fertilizers and other amendments during the improvement period increased the soil carbon content by an average of 2.16%,which significantly improved the soil environment in the tillage layer of the study area and increased the safety zone for crop growth,making it more favorable for crop growth.(3)The burial depth of groundwater was positively correlated with its mineralization and negatively correlated with soil salinity.The depth of groundwater increased by 0.35 m during the improvement period,the mineralization increased by 0.18g/L,and the soil salinity decreased.The groundwater depth is controlled between 1.8?2.2m,which is beneficial to crop growth and can avoid aggravating the secondary salinization of soil to a certain extent.The groundwater level is 2.13 m after improvement,which indicates that the implementation of agricultural water conservancy engineering infrastructure construction projects such as ditch dredging and remediation and channel lining effectively controls the groundwater level and weakens the negative impact of groundwater on soil salinity.(4)With the increase of groundwater burial depth during the improvement period,the total net input of salt from groundwater to 1m soil layer year by year was 0.3650,0.2821,0.1847 million t,decreasing year by year,and the amount of salt diverted by irrigation water from 2018 to 2020 was 1.83,1.68,1.82 million t,and the amount of salt discharged by open ditch drainage was 1.59,1.55,1.62 million t,respectively,and the open ditch Salt discharge efficiency is 72.54%,79.25%,80.74%,the amount of salt discharge is improving year by year,1m soil salt accumulation(desalination)from 2018to 2020 is 16.58,-12.66,-23.665kg/mu,the study area improvement period salt control effect and salt discharge efficiency improved year by year,the root layer soil from salt accumulation to desalination,soil and water environment improved year by year,indicating that agricultural water conservancy This shows that the construction of agricultural water conservancy infrastructure and the implementation of the"five-in-one"comprehensive improvement measures are effective in improving saline soils in saline irrigation areas.(5)Through sorting and analysis,two types of evaluation index systems were developed:the first type of system includes four primary indicators(soil salinity,crop growth,soil strength and economic efficiency indicators),eight secondary indicators(total salt,alkalinity,seedling retention rate,yield,organic matter,total nitrogen,volumetric quality,input-output ratio),and the service targets are enterprises that apply soil improvement products or models to demonstrate improvement effects,with the purpose of excellent The second type of system includes four primary indicators(soil salinity,soil strength,economic and social benefits and environmental benefits)and eight secondary indicators(total salt,alkalinity,organic matter,total nitrogen,volumetric quality,input-output ratio,development of technical regulations or standards,heavy metal load),and the service targets are scientific research institutes and transfer enterprises,and the annual target achievement is the evaluation purpose.(6)The weight coefficients of each index of the evaluation system,evaluation rules and classification standards were determined,and the evaluation index system of saline land improvement was finally constructed and the improvement effect of improvement enterprises and experimental units in the experimental area was comprehensively evaluated.Four kinds of improvement products were selected,including organic fertilizer and biodynamic regulator for saline land.