Research On Efficient Use Of Brackish Water For Cotton Under Drip Irrigation With Membrane

Object:Scientific and reasonable use of brackish water resources for agricultural irrigation can not only save freshwater resources and alleviate the situation of water stress,but also have the effect of drought resistance and yield increase,which is of great significance to ensure sustainable agricultural development and maintain social stability.In this thesis through the study of brackish water irrigation experiment for cotton under membrane drip irrigation,we elucidated the effect of brackish water under membrane drip irrigation on soil environment and cotton physiological growth in cotton fields,explored the mechanism of different irrigation water mineralization degrees on soil carbon emission in cotton fields,clarified the utilization potential of brackish water with different mineralization degrees,and provided theoretical support for realizing carbon sequestration and emission reduction in cotton fields and enriching the technology system for efficient utilization of brackish water in cotton in Xinjiang region.Methods:This experiment was conducted in 2021 and 2022 at Shihezi University water-saving irrigation experimental station,with cotton under film drip irrigation as the research object,and four gradients of irrigation water mineralization（made by using industrial salt and local irrigation water blending）with treatment numbers CK,S1,S2,and S3 were set up to conduct a field trial study.Results:（1）The soil salinity of the brackish water drip irrigated cotton field showed an increasing trend with the increase of irrigation water mineralization,and the salinity gradually accumulated in the soil depth of40～60 cm as the cotton growth period progressed.The use of 8 g/L irrigation water for under-membrane drip irrigation caused a significant increase in soil water content and conductivity and a significant decrease in soil nitrate nitrogen content,resulting in soil nutrient loss,affecting crop growth and reducing soil respiration rate.Irrigation water mineralization of 3 g/L and 5 g/L increased soil water content and conductivity in cotton fields and inhibited soil respiration,but did not significantly affect soil mineral nitrogen content.（2）Influenced by the mineralization of irrigation water,soil respiration in cotton fields was mainly related to the soil temperature from 0 to 10 cm,and the relationship between them could be characterized by a quadratic equation,and 26.9℃was the most suitable soil temperature for soil respiration.Under brackish water irrigation,soil moisture was no longer the soil parameter limiting soil respiration rate,and the correlation between soil conductivity and soil mineral nitrogen and soil respiration rate was enhanced.With increasing mineralization,soil conductivity not only acted directly on soil respiration,but also indirectly affected soil respiration rate by suppressing changes in soil temperature and soil nitrate-nitrogen content.（3）Under-film drip irrigation with irrigation water with mineralization less than 3 g/L did not significantly affect the physiological growth of cotton and could guarantee the crop yield.Under-membrane drip irrigation with 8 g/L irrigation water significantly reduced net photosynthetic rate,transpiration rate and stomatal conductance of cotton,increased intercellular CO₂ concentration of cotton,thus reducing plant height,stem thickness and leaf area index of cotton,inhibiting crop growth,reducing its above-ground biomass accumulation and reducing crop yield.（4）Sub-membrane drip irrigation with brackish water increased increased the break ratio strength of cotton fibers,increased the Markelon value,and generally reduced the quality of cotton.3 g/L of irrigation water could improve the water-carbon use efficiency of sub-membrane drip irrigated cotton.Conclusion:In summary,the use of irrigation water less than 3 g/L under film drip irrigation can increase cotton yield,improve water utilization efficiency,reduce soil respiration rate and reduce farmland carbon emissions without significantly increasing soil salt content,which is the appropriate salinity range of irrigation water under brackish water film drip irrigation in Xinjiang.