Study On Improvement Of Saline-Alkali Soil By Drip Irrigation Leaching Combined With Underground Pipe And Shaft Drainage

Objective:Excessive irrigation and flood irrigation are usually used to discharge farmland soil salinity in Xinjiang,but this leads to groundwater table elevation and poor salt discharge,which directly affects soil nutrients and microbial environment,and indirectly affects crop yield.Therefore,reasonable combination of irrigation and drainage measures can improve saline-alkali land while ensuring the stability of agricultural ecological environment.Methods:taking the typical arid and salinized farmland in Xinjiang（cotton field in An Ji Hai Township,Shawan County）as the research object,based on the research results of underground pipe drainage experiment in this area from 2016 to 2017,we carry out twice the combined drainage test of underground pipe and shaft from May 2020 to October 2021,and monitoring the soil water and salt,physical and chemical properties and cotton growth indexes in two consecutive growth periods.Three treatments of 0m（P1）,5m（P2）,7.5m（P3）away from the underground pipe and four treatments of 5m（S1）,15m（S2）,30m（S3）and60m（S4）away from the shaft were set up.Through the collaborative improvement of saline farmland by drip irrigation leaching combined with underground pipe and shaft drainage test,the spatial and temporal distribution and variation law of drainage-salt were analyzed,and the response of soil nutrients,ions,soil enzyme activity and soil microbial community diversity under collaborative improvement were discussed.Compared with single underground pipe drainage mode,the improvement effect of underground pipe and shaft drainage on saline soil was clarified.Results:（1）After drip irrigation combined with subsurface pipe and shaft drainage,the water content in400～700 cm soil layer was higher than that in shallow soil layer,while the desalination rate was opposite.The combined drainage reduced the soil electrical conductivity of 0～200 cm in the test area by 73.1%on average,which was 8.3%higher than that of the single use of subsurface pipe drainage from 2016 to 2017.In addition,the soil electrical conductivity of 200～700 cm in the test area also decreased by 75.5%on average,which has changed from the single subsurface pipe drainage to the combined drainage of subsurface pipe and shaft.And the groundwater level decreased by 30%compared with the single pipe drainage measures,and the groundwater level decreased by about 2 m compared with the single pipe drainage measures.（2）The distribution trend of total nitrogen content in each treatment was similar,and the total nitrogen content in 2021 increased by 0.63～1.88 times on average compared with the same period last year.The average concentrations of Cl^-and Na⁺in soil decreased by 17.2%and 15.8%,and the average contents of Ca²⁺and K⁺increased by 165.6%and 38.8%.The microbial dominant species（phylum level）were more evenly distributed.The activities of catalase,phosphatase and protease increased by 14.2%,6.4%and 8.1%on average,and the activities of urease and sucrase decreased by 3.7%and 2%on average.（3）The leaf area index and plant height of cotton under drip irrigation combined with subsurface pipe and shaft drainage mode were 1.2 and 1.6 times higher than those under single subsurface pipe drainage mode,and the dry matter weight of cotton increased by 31.8%～83.15%in the second year after irrigation.The yield index increased by 18%（single boll weight）,8%（seed cotton yield）and 12%（lint yield）compared with the single drainage mode.This indicated that leaching reduced soil salinity,resulting in the decrease of Cl^-,Na⁺content,urease activity and relative abundance of Firmicutes in soil,which promoted the growth index and yield of cotton.Conclusion:The results reveal the salt drainage effect and soil improvement effect under the collaborative improvement mode of drip irrigation under mulch combined with underground pipe and shaft drainage,and provide scientific reference for improving crop yield and reasonably preventing soil salinization in inland arid and salinization areas.