Abstract: Increasing plant density under insufficient or lowirrigation conditions is a new water-saving production technology for cotton, especially in the dry and short growing season cotton regions of Xinjiang, China. Increasing planting density would increase canopy coverage and total water consumption, and change rhizosphere salt distribution. We conducted a field experiment with three planting densities (low density M1, 135000 plants·hm^-2; medium density M2, 180000 plants·hm^-2; high density M3, 225000 plants·hm^-2) and three irrigation quota\[severe- deficit W1 (50% ET_C, crop water demand), 3150 m³·hm^-2; mild deficit W2 (75% ET_C), 4050 m³·hm^-2; full irrigation W3 (100% ET_C), 4980 m³·hm^-2\], to analyze their effects on 0-60 cm soil salt content, uniformity coefficient, surface accumulation coefficient, variation, and salt rejection rate. The results showed that with increasing planting density, soil salt content and surface accumulation coefficient were significantly reduced, while the uniformity of salt distribution increased. Increasing irrigation quota reduced soil salt content of different planting densities, but the salt distribution gradually changed from the “bottom accumulation in the film” to “surface accumulation in the film”, and the uniformity of which was significantly reduced. In addition, there were significant differences in salt change and salt rejection rate under different treatments. With increasing planting density, salt change and rejection rate were gradually reduced, and the results were completely opposite with increasing irrigation quota. The combinations of low density + mild deficit irrigation, medium density + full irrigation, and high density + full irrigation led to the greatest change in salt content and the highest rejection rate, which were 0.041 g·kg^-1 vs. 18.2%, 0.041 g·kg^-1 vs. 25.6%, and 0.055 g·kg^-1 vs.30.50%,respectively. The sensitivity of soil salt to different irrigation quota depended on planting density. When the irrigation quota fall into the range of 3150-4050 m³·hm^-2 (50%-75% ET_C), planting density is recommended to be 135000 plants·hm^-2; when the irrigation quota is 4980 m³·hm^-2 (100% ET_C), the planting density to be 180000-225000 plants·hm^-2,which can effectively reduce soil salinization level, conserve water, and maintain a higher productivity level. Our results provide reference for reasonable selection of planting density and irrigation quota with drip irrigation under plastic films in machine-harvested cotton fields.

Key words: planting density, irrigation quota, machine-harvested cotton, soil salinity, salt movement.