Experimental Study On Improving Salt Leaching Effect Of Coastal Saline Soil By Adding Straw And Gypsum

The saline alkali soil in the newly reclaimed irrigation area of Jiangsu coastal beach has high salt content,poor soil structure and poor drainage,and the output speed of salt with drainage is slow.Chemical soil improvers can be used to improve the soil structure by increasing soil organic matter,and the discharge of harmful salt ions in the soil can be accelerated by chemical ion replacement.This study discussed the effect of adding straw and gypsum modifier on accelerating the desalination process of newly reclaimed soil in coastal areas.Through indoor soil column test,the effects of adding straw and gypsum on the change of salt composition and leaching effect of saline soil were studied.On the basis of the experiment,the hydrous-1d model is used to construct a dynamic model of water and salt of coastal saline soil with straw and gypsum as modifier,simulate the soil desalination effect of soil column with gypsum and straw as modifier in different leaching modes,and explore the soil desalination effect of straw and gypsum in different rainfall typical years by using the long-series meteorological data of the study area,The application effect of straw and gypsum as soil conditioner was analyzed.The main research results of this paper are as follows:(1)The physical and chemical properties of leached soil showed that the chemical improvement treatment with gypsum greatly improved the saturated hydraulic conductivity of soil,and the average value of straw in the two groups increased by 266.3%compared with the control group.After leaching,the ECE and SAR of saline soil decreased significantly,and reached the desalination standard after three leaching cycles(PV).When straw was applied to soil improvement,the stability of soil aggregates did not increase significantly.Compared with the initial measured value of soil before leaching,the stability of soil water stable aggregates increased by 24.2%and 28.9%respectively.(2)The chemical properties of the leaching solution showed that in the treatment of adding gypsum and straw,the ion components of the leaching solution of saline soil were different,and the emission of K+and Mg2+ ions were similar under different treatments.Gypsum can provide divalent cations for soil and promote the exchange of Na+in soil.Compared with the treatment of adding gypsum alone,straw+gypsum group can leach more soluble Na+ ions and reduce soil SAR more effectively.(3)The soil ECE at the observation point is negatively correlated with the leaching times and positively correlated with the potential evaporation intensity(EP).The addition of straw can effectively reduce the soil ECE value,but the effect decreases gradually with the increase of leaching frequency.The desalting effect of two times of leaching is better than that of four and ten times.(4)There is abundant rainfall in wet years,and the difference of desalination effect between the four test groups is not obvious.All the four test groups meet the desalination standard.The rainfall intensity in normal water year is high and concentrated,and only the gypsum group does not meet the desalination standard.The effect of straw mulching group was the best in dry years.Long term simulated gypsum leaching soil,resulting in the increase of soil salt content.