Deficit irrigation combined with a high planting density optimizes root and soil water–nitrogen distribution to enhance cotton productivity in arid regions

Increasing the cotton planting density can reduce irrigation while maintaining the seed cotton yield. However, the underlying physiological and ecological mechanisms remain unclear. We hypothesized that increasing the planting density and reducing irrigation would promote dynamic consistency in the distribution of the roots, soil water, and nitrogen, leading to improved cotton water productivity and ultimately achieving a stable seed cotton yield. To test this hypothesis, a 3-year field experiment (2019–2021) was conducted in Xinjiang, China. The main plots were subjected to 3 irrigation levels based on crop evapotranspiration (ETc): 0.6 (deficit), 0.8 (typical), and 1.0 ETc (adequate). Subplots were planted at 3 densities: 13.5 (low), 18.0 (typical), and 22.5 plants m −2 (high). Under typical irrigation conditions, the seed cotton yield was significantly higher at a typical planting density than at a low or high planting density. However, with adequate irrigation, a low planting density resulted in a higher yield, while a high planting density combined with adequate irrigation reduced the yield by 14.7 % compared with typical conditions (typical irrigation + typical planting density). Under deficit irrigation, the seed cotton yield at a high planting density was 9.2–23.5 % higher than that at a low or typical planting density, achieving yield stability with 20 % water saving. The dry matter accumulation and harvest index showed no significant differences between typical irrigation + typical planting density and deficit irrigation + high planting density. Deficit irrigation combined with a high planting density resulted in a higher overlap rate of the root distribution area, soil water consumption area, and nitrate nitrogen consumption area, leading to higher water productivity than that of other density and irrigation combinations. Deficit irrigation combined with a high planting density can reduce water input by 20 % without sacrificing cotton yield, likely because of increased water productivity through the enhanced dynamic consistency of root distribution and soil water-nitrogen consumption. These findings provide valuable ecological and physiological insights for achieving water savings without compromising yield in arid and water-scarce regions. • Deficit irrigation at high planting density maintains seed cotton yield. • Deficit irrigation at high planting density increases water productivity. • Deficit irrigation at high density improves consistency of root distribution and soil water-nitrogen consumption. • This consistency contributes to increased water productivity and yield stability.