Study On Salt Tolerance Threshold And Regulation Technology Of Cotton Root Zone Under Mulch Drip Irrigation

Objective:The shortage of freshwater resources and soil salinization seriously restrict the development of agriculture in Xinjiang.As a salt-tolerant pioneer crop,cotton has become a major economic crop in Xinjiang through its promotion and the growing area of cotton.This study explored the effects of different initial soil salt content,different irrigation quota,and salinity on the water and salt transport and the physiological growth,yield,and quality of cotton under mulch drip irrigation.Through the salt production function and mathematical model,the salt tolerance threshold and critical irrigation value of drip irrigation cotton at different growth stages were determinedMethods:The orthogonal experiment of three factors and four levels was carried out in the cotton growth period in 2022.Set four different soil initial salt content（T1:2.0 g/kg,T2:4.0 g/kg,T3:6.0g/kg,T4:8.0 g/kg）,four irrigation quotas（W1:3375 m³/hm²,W2:3750 m³/hm²,W3:4125 m³/hm²,W4:4500 m³/hm²）,and four irrigation salinity（S1:2.0 g/L,S2:5.0 g/L,S3:8.0 g/L,S4:11.0 g/L）.Results:（1）In the 10～40 cm soil layer,the soil mass moisture content and soil conductivity increased with depth.When the irrigation quota is fixed,the soil mass moisture content of the treatment with high initial soil salt content and high irrigation salinity is higher than that of the treatment with low initial soil salt content and low irrigation salinity.The soil conductivity fluctuates with time.（2）Plant height,stem diameter,leaf area,transpiration rate,net photosynthetic rate,stomatal conductance,the maximum photochemical quantum yield of PSⅡ,maximum fluorescence of leaves,the potential activity of PSⅡ,and aboveground biomass.The treatment with a high irrigation quota,low irrigation salinity,and low soil initial salt content is superior to the treatment with a low irrigation quota,high irrigation salinity,and high soil initial salt content.Non-photochemical quenching and intercellular CO₂ concentration are contrary to the law.（3）Through path analysis of cotton physiological growth index and yield index,the correlation coefficient between boll number per plant and yield is the largest,0.86.The direct path coefficient is0.49,and the indirect path coefficient is 0.37;The correlation coefficient between net photosynthetic rate and yield was 0.74,the direct path coefficient was 0.20,and the indirect path coefficient was 0.55;The correlation coefficient between non-photochemical quenching and yield is-0.80,the direct path coefficient is-0.34,and the indirect path coefficient is-0.46.The direct effect of boll number per plant on yield was the largest,and the indirect effect of net photosynthetic rate was the largest.（4）The principal component analysis of the cotton yield index and quality index showed that the first principal component（PC1）was significantly positively correlated with the number of bolls per plant,weight per boll,yield,irrigation water use efficiency,uniformity index,and elongation;The second principal component（PC2）was significantly positively correlated with the number of bolls per plant,yield,irrigation water use efficiency,the average length of the upper half and breaking ratio intensity.The best treatment was the T3W4S2 treatment,with a score of 1.26,and the worst treatment was the T4W1S4 treatment,with a score of-1.84.（5）Using the salt production function,it can be seen that the sensitivity of cotton to salt varies at different growth stages,showing the rule of bud stage>flowering and boll stage>boll opening stage.Salt tolerance threshold of cotton at different growth stages:0.79～1.19 m S/cm at the bud stage,0.86～1.32 m S/cm at flowering and boll stage,1.71～1.97 m S/cm at the boll opening stage.（6）The genetic algorithm is used to optimize the solution by establishing the ternary quadratic equation.When the initial salt content of the soil is 0.20%,and the salinity of irrigation water is 11.00 g,the critical value of irrigation water in the bud stage is 506.81 m³/hm²;When the initial salt content of the soil is 0.80%and the salinity of irrigation water is 2.02 g,the critical value of irrigation water at flowering and boll stage is 2698.27 m³/hm²;When the initial salt content of the soil is 0.80%and the mineralization degree of irrigation water is 1.96 g,the critical value of irrigation water in the period of floc opening is 549.05 m³/hm².The research results can preliminarily reveal the response mechanism of cotton yield to soil water and salt stress and provide the specific scientific theoretical basis for water and salt regulation and saline soil management in arid and semi-arid areas of northwest China.