| In order to achieve long-term brackish water drip irrigation under membrane cotton root zone will not appear obvious salt deposition caused by soil salinization and can be popularized in arid areas of irrigation system.This paper set 9 group of elution fractions and a set of fresh water as the control group for carrying out film with drip irrigation cotton experiments at Mongolia autonomous prefecture in tarim river basin irrigation experimental station.During the growth cycle of cotton,water content(volumetric water content/field water holding capacity)and soil conductivity at different section depths in the root area of cotton were manually monitored before each drip irrigation for exploring the influence on water and salt transport in the root area with different leaching fractions.The sample method was used to monitor the yield of seed cotton to determine the leaching demand,and the principal component analysis and TOPSIS analysis were used to obtain the best washing salt scheme for popularization.The main research results are as follows.(1)The higher content of sodium ions in brackish water changes the soil structure and reduces the permeability coefficient of soil.Compared with fresh water,the water flow in the vadosperm zone of cotton field under brackish drip irrigation is shallower in the same time interval.(2)The salinity of brackish water has a significant effect on the salt accumulation in cotton root region.Under brackish water drip irrigation film,the root region of cotton with 0～30cm presents a "low-salt zone",and the deepest part of the "low-salt zone" is 30 cm.(3)With the increase of the leaching fraction,the amount of water remaining in the main root area(0～30cm section)gradually increase in the growth cycle of cotton within the same time interval.When the leaching fraction is greater than or equal to 0.25,insufficient gravity water release will occur in the main root area within a single irrigation interval(5d).At the same time,the degree of water alternations in the 30～60cm root section also increase with the increase of the leaching fraction,which is conducive to the leaching of salt in the root region by soil water.(4)The minimum leaching fraction of salt accumulation in the root section before and after the planting period of cotton under membrane drip irrigation in the arid region is 0.1.When the leaching fraction is 0～0.1,with the increase of the leaching fraction,the variation amplitude and trend of the profile in the taproot region(0～30cm)decrease in turn during the planting period of cotton.And with the increase of the leaching fraction,this depth gradually expand.When the leaching fraction is 0.25,the root region(0～40cm)forms a stable "low-salt zone" in the whole cotton growth cycle.(5)The cotton yield of the 9 groups are 4222kg/ha～6243kg/ha,and the highest cotton yield is 0.15.Principal component analysis shows that the absolute value of component matrix of cotton yield,drip irrigation water and cotton yield are all greater than 0.9,and the three evaluation factors have good correlation.According to the TOPSIS comprehensive scoring method,the scores of 9 groups of leaching experiments range from 0.000778 to 0.685626,and the corresponding optimal scheme is LF=0.15. |
