Effects Of Soil Matrix Potential Regulated Irrigation On Cotton Growth And Soil Water,Heat And Salt Distribution In Northern Xinjiang

Considering the challenge of water shortage and soil salinization in Northern Xinjiang,a field experiment was conducted in Shihezi City,Xinjiang from April to September in2020.The“Xinluzao 42”was selected as the experiment variety,the lower limit of soil matrix potential（SMP）at 20 cm below the dripper during irrigation period was-40 k Pa as the CK.Three SMP W₁（-10 k Pa）,W₂（-20 k Pa）and W₃（-30 k Pa）were set at the seedling stage（A）,seedling stage+budding stage（B）,seedling stage+budding stage+flowering and bolling stage（C）to regulate the irrigation level.A total of 10 treatments were used to determine the cotton growth,yield,soil moisture content,temperature and salt content of different soil matrix potential control treatments.Finally,the effects of different treatments were comprehensively evaluated by TOPSIS method.This experiment studied the effects of SMP regulation at different growth stages on cotton growth,yield and soil water,heat and salt distribution,so as to provide a theoretical basis for the selection of water-saving,salt controlled and efficient irrigation systems in cotton fields in Northern Xinjiang.The following are the results of the study.（1）Under the same SMP thresholds level,regulated irrigation at different growth stages had significant effects on plant height,stem diameter,leaf area index（LAI）and SPAD value,which were in the order of WC>WB>WA>CK.With the increase of SMP level,plant height,stem diameter,LAI and SPAD value increased significantly.In the seedling stage,each growth index of cotton is small.In this period,the higher SMP regulation irrigation has no obvious effect on the growth of cotton,and each index reaches the peak in the flowering and bolling stage.The plant height of W₁C increased by 28.7%and 50.7%respectively compared with W₃C and CK,the leaf area index increased by 14.2%and 13.4%respectively compared with W₂C and W₃C,and the SPAD value increased by8.4%and 9.1%respectively;Compared with WA,WB and CK treatments,the average stem diameter of WC increased by 26.2%,30.1%and 40.2%respectively.The growth of cotton can be promoted when the SMP level is controlled at about-20～-10 k Pa in different growth stages.（2）Under the same SMP irrigation level,the aboveground dry matter quality and seed cotton yield under regulated irrigation in different growth stages showed the trend of WC>WB>WA>CK.With the increase of SMP,the dry matter mass of cotton boll,root,stem and leaf increased,and the treatment of W₁ and W₂ was significantly higher than that of W₃ and CK.The cotton yield showed an increasing trend.The yield of W₁C treatment was the highest,which was 5.6%and 11.3%higher than that of W₂C and W₁B.At the same time,the water consumption of cotton gradually increased and the water use efficiency decreased slightly.The average length of the upper half of cotton regulated by higher matrix potential is larger,the micronaire value is smaller,the elongation at break is smaller,and the fiber uniformity is at the high-grade level.TOPSIS analysis method is used to obtain the optimal treatment（W₂C）under the comprehensive evaluation of various indexes.Under the condition that cotton can obtain high yield and quality while ensuring a certain water use efficiency,the SMP should be controlled at about-20 k Pa.（3）Under the same regulation level of SMP,the soil moisture content of 0～100 cm soil layer is basically WC>WB>WA>CK.With the increase of SMP,the soil moisture content increased significantly.The soil moisture contents of W₁C and W₂C treatments were 21.2%and 17.6%.The soil temperature decreases with the advance of the growth period,and gradually decreases with the deepening of the soil layer.The peak time lags behind and the fluctuation amplitude decreases.The daily average temperature of the growth period in the film is 28.7℃,which is 1.5℃higher than that outside the film.With the increase of SMP level,the temperature in the film increased gradually in the seedling stage,the warming effect of 10～20 cm soil layer was more obvious,and the soil temperature in the flowering and bolling stage and boll opening stage decreased slightly with the increase of SMP level.At the end of the growth period,the content of soil salt is the least under the drip irrigation zone,and the salt content outside the film is higher than that inside the film.The salt is mainly accumulated in the soil layer of 50～70 cm.Under the same SMP irrigation level,the average value of relative desalination rate of 0～100 cm soil layer in different growth stages showed WC>WB>WA.Under the control of the same growth period,with the increase of SMP level,the better the soil desalination effect,the greater the average relative desalination rate,and the desalination amount in the membrane is higher than that outside the membrane.The desalination effect of W₁C and W₁B treatment was better than that of other treatments,and the average relative desalination rates were 175.16%and 152.44%respectively.Controlling the SMP at-20～-10 k Pa can ensure to provide a more suitable soil hydrothermal environment and control soil salinity under the condition of meeting the growth needs of cotton.（4）The comprehensive analysis of TOPSIS showed that the W₂C treatment was more conducive to cotton growth and development,yield formation and higher water use efficiency and better desalination effect.Under the condition of ensuring water-saving,salt control and efficient production in cotton fields in Northern Xinjiang,it is recommended to implement-20 k Pa SMP regulated irrigation in seedling stage,budding stage and flowering and bolling stage as the best irrigation management.