Effect Of Mulched Drip Irrigation Under Saline Water On Soil Physicochemical Properties And Crop Growth

The underground saline water resources in Hetao Irrigation District（HID）are abundant,the spatial variability of water quality is large,and the problem of soil salinization is becoming more and more serious.HID is an important commodity grain base in China.There is a risk of soil structure deterioration in saline water irrigation in many areas of HID.In this study,corn was planted in the form of drip irrigation under film in Shuguang Experimental Station of HID in Inner Mongolia during the corn growing season（May to September）from 2021 to2022,and field positioning test of saline water irrigation was carried out.Underground water was taken as a control（CK）.The same concentration and different types of chloride salts were added into the groundwater(20 mmol_c·L^-1)respectively to form different treatments（Na Cl,KCl,Ca Cl₂ and Mg Cl₂,labeled as T1,T2,T3 and T4 respectively）.These formed similar conductivity（EC）and different cation composition saline water treatment.Soil physical properties（soil water content,soil water holding capacity and pore structure characteristics）,chemical properties（soil EC_e,p H,ion concentration in root zone,Sodium Adsorption Ratio and Cation Ratio of Soil Structural Stability）,crop growth indicators（plant height,LAI and yields）and ion absorption content of crop organs were measured.The characteristics of soil pore structure,the spatial and temporal distribution of water and salt,and the response mechanism of crop growth were studied.The effects of saline water with different cation compositions on soil physical and chemical properties and crop growth under drip irrigation under mulch were analyzed.The research results can provide theoretical basis for safe utilization of underground saline water in the HID.The main conclusions are as follows:（1）The results showed that more Na⁺and K⁺in irrigation water would deteriorate soil pore structure,while Ca²⁺and Mg²⁺had a beneficial effect on soil pore structure.A two-year field experiment found that the addition of monovalent cations such as Na⁺and K⁺to irrigation water could lead to serious or mild deterioration of soil pore structure.At the same time,the soil porosity and rounding rate were reduced,the soil connectivity was weakened,the water infiltration of the soil surface is reduced,and the water storage effect of the deep soil is reduced.In contrast,Ca²⁺and Mg²⁺could effectively improve soil macroporosity and roundness,stabilized soil macropore morphology and improved soil connectivity,which was conducive to improving the infiltration performance of soil surface water and was conducive to crop absorption of water and fertilizer.（s）More Na⁺in irrigation water increased soil p H,SAR and CROSS.The addition of Ca²⁺and Mg²⁺reduced soil p H,SAR and CROSS,and alleviated the salinization of soil surface.Compared with CK,T2 treatment had no obvious salt accumulation.T1,T3 and T4treatments produced salt accumulation in different regions of the soil.T1 treatment accumulated more salt in the surface soil of crop root zone,which was not conducive to the further infiltration of irrigation water.The salt of T3 and T4 treatments accumulated outside the film.The experiment showed that more Ca²⁺and Mg²⁺in irrigation water could make more salt move out of crop growing area with water evaporation and reduce salt stress in crop root zone.Based on the two-year experiment,with the increase of irrigation times,the p H of 0-40cm soil in T1 and T2 treatments showed an upward trend,which was not conducive to the improvement of alkalized soil.The soil p H of T3 and T4 treatments decreased year by year,and T3 treatment had the best effect on reducing soil p H and reducing the degree of salinization of soil surface.The results showed that the addition of appropriate concentrations of Ca²⁺and Mg²⁺could significantly reduce the concentration of Na⁺in soil solution,reduce SAR and CROSS in crop root zone soil,and improve the soil water and salt environment in crop root zone.（3）The results showed that the appropriate concentration of K⁺,Ca²⁺and Mg²⁺in irrigation water could improve the dry weight accumulation and the final yield of crops.Under the condition of saline water irrigation,the increase of Na⁺concentration in the aboveground organs of corn significantly reduced the plant height,LAI and the accumulation of dry matter in stems and leaves,and the crop yield tended to decrease.Compared with the negative effect of more Na⁺,the appropriate concentration of K⁺,Ca²⁺and Mg²⁺in irrigation water was helpful to improve the dry matter accumulation of crops and the final yield formation.The results showed that Mg²⁺had the best effect on improving the biomass and yields of corn.Therefore,in view of the moderate salinization farmland in HID,considering the physical and chemical properties of soil and the water and salt environment of crop root zone,the appropriate concentration of Ca Cl₂ and Mg Cl₂ was added to reduce the concentration of Na⁺in soil under the irrigation of saline water with high concentration of Na⁺,so as to improve the soil pore structure and water and salt environment,and improve the dry matter accumulation and yield of crops.