Spatiotemporal dynamics of rhizosphere soil water, temperature and salinity under various drip irrigation regimes and their effects on cotton biomass formation

Optimizing drip irrigation regimes is critical for managing the rhizosphere soil environment and enhancing cotton productivity in arid regions. A two-year field experiment (2023–2024) was conducted in northern Xinjiang, China, with four irrigation levels (60%, 80%, 100%, and 120% of crop evapotranspiration, denoted as W1 to W4). High-resolution in-situ sensors monitored soil water content, temperature, and electrical conductivity hourly at 10–100 cm depths, and a Logistic model was employed to analyze biomass responses. High irrigation (W4) promoted water infiltration to 60–80 cm depth and stimulated taproot elongation, whereas low irrigation (W1) restricted water to 30–40 cm and inhibited taproot growth. Increased irrigation reduced soil effective accumulated temperature (W4 decreased by 6.37% in 2023 and 7.74% in 2024 compared to W1) but enhanced salt leaching to deeper layers. The Logistic model identified initiation thresholds for rapid biomass accumulation: vegetative organs began to accumulate rapidly at approximately 500 °C and 50 mm (reaching the plateau phase at approximately 200 mm and 900 °C), whereas reproductive organs required > 800 °C, with water consumption thresholds varying by treatment (approximately 150 mm under W1, 180–220 mm under W2 and W3, and 250–300 mm under W4). Path analysis indicated that irrigation amount primarily governed biomass by directly regulating soil water, which promoted taproot elongation and water consumption, forming a positive feedback loop. This study demonstrates that drip irrigation regimes co-regulate cotton growth by mediating the synergistic spatiotemporal variations of water, temperature, and salinity in the rhizosphere, providing a theoretical basis for precision irrigation management aimed at water-saving, salt control, and high productivity in arid cotton production.