Irrigation Decision Parameters for Cotton in Arid Xinjiang Based on Growth-Stage-Specific Soil Moisture Thresholds

Water scarcity critically constrains sustainable cotton production in arid Xinjiang, China. Conventional irrigation management often relies on empirical decision-making, resulting in a dynamic mismatch between water supply and the growth-stage-specific water demands of cotton, thereby constraining the full potential of agricultural water resources. A transition from experience-based irrigation to quantitative parameter-driven smart decision-making is urgently required. Smart irrigation requires soil moisture thresholds tailored to different growth stages to serve as irrigation decision parameters. To identify refined irrigation parameters that reconcile high yield with enhanced water productivity, this study conducted a two-year field experiment in northern Xinjiang, imposing distinct lower and upper soil moisture limits (expressed as % of field capacity, FC) across seedling, budding, flowering and boll, and boll opening stages. Treatment effects on soil moisture dynamics, plant growth, yield, water use efficiency (WUE), and irrigation water productivity (IWP) were systematically evaluated. Synergistic optimization of yield and WUE identified optimal thresholds: lower limits of 50–54% FC at seedling, 56–61% FC at budding, 74–76% FC at flowering and boll, and 53–57% FC at boll opening; upper limits were 100% FC for all stages except boll opening, set at 85% FC. Relative to conventional farmer irrigation decision-making, threshold-based irrigation saved 13.41% water, increased seed cotton yield by 10.72%, and enhanced WUE and IWP by 42.31% and 28.10%, respectively. This study provides irrigation decision parameters derived from soil moisture thresholds across different growth stages and planned wetted layer depths, offering directly embeddable engineering inputs for smart drip irrigation platforms to enable precise, demand-driven water management and establish a technical foundation for precision irrigation in the arid cotton fields of Xinjiang.