Abstract: 【Objective】Discuss the appropriate conductivity threshold value of the brackish water irrigation for the film residual cotton field in southern Xinjiang,and clarify the feasibility plan of the brackish water instead of fresh water irrigation in the residual film soil cotton seedling stage.【Methods】The experiment adopted four factors and three levels orthogonal design of the amount of residual film,irrigation water control limit,soil bulk density and irrigation water conductivity,and carried out pot experiment to analyze the influence of experimental factors on chlorophyll content,nitrogen balance index and water consumption of cotton seedlings.【Results】The irrigation water conductivity was the main factor affecting the chlorophyll content and nitrogen balance index of cotton seedlings. As the irrigation water conductivity increased,the chlorophyll content decreased from 41.67 μg/cm² to 33.18 μg/cm²,and the nitrogen balance index decreased from 60.52 to 39.20. On the first day after irrigation,as the amount of film residue increased,soil water consumption increased from 6.68% to 8.13%;as the irrigation water control limit increased,soil water consumption increased from 7.13% to 8.10%;as soil bulk density increased,soil water consumption decreased from 7.59% to 7.39%;with the increase of irrigation water conductivity,soil water consumption increased first and then decreased,increasing from 7.12% to 7.69% and then decreasing to 7.54%.【Conclusion】Increasing the conductivity of irrigation water and the amount of soil film residue in the film residue cotton fields in southern Xinjiang would reduce the chlorophyll content and nitrogen balance index of cotton seedling stage,and increase the ineffective water consumption of the soil. In the soil with film residue,the amount of residual film was 240 kg/hm² and the conductivity of irrigation water was 2 500 μS/cm as the appropriate conductivity threshold value. The optimal combination of factors when the chlorophyll content and nitrogen balance index reached the maximum was as follows：the amount of residual film was 240 kg/hm²,the irrigation water control limit was 60% field water holding capacity,the soil bulk density was 1.3 g/cm³,and the irrigation water conductivity was 2 500 μS/cm.

Key words: Brackish water, Soil film residue, Cotton, Chlorophyll, Nitrogen balance index, Water consumption