In arid and semi-arid regions, improving water use irrigation efficiency under limited seasonal water supply is critical for sustainable cotton production. While the effects of seasonal irrigation amount have been widely studied, the independent and interactive roles of irrigation interval under a fixed seasonal irrigation constraint remain insufficiently quantified. This study aimed to evaluate how irrigation amount and interval jointly regulate soil water dynamics, evapotranspiration partitioning, yield formation, and water use efficiency (WUE) in cotton. A two-year, controlled soil-column experiment was conducted using a full-factorial design with two seasonal irrigation amounts (350 and 200 mm) and four irrigation intervals (every 3, 6, 9, or 12 days). The AquaCrop model was locally calibrated with 2024 data and validated with independent 2025 observations. The validated model was then used to conduct scenario simulations across 16 irrigation combinations to analyze process-level responses. The model reproduced canopy cover and soil water storage (SWS) dynamics with good accuracy (R² > 0.89; NRMSE < 16%). The results showed that irrigation amount primarily controlled overall water availability, whereas irrigation interval reshaped the temporal fluctuation pattern of soil water content (SWC) in the shallow root zone. Under moderate irrigation levels, an intermediate interval (every 6 days) improved WUE by stabilizing SWC and maintaining high transpiration proportions. Under severe deficit conditions, prolonged intervals intensified periodic water stress and reduced yield. Simulated transpiration accounted for 95–97% of seasonal evapotranspiration in the controlled system, reflecting limited soil evaporation under column conditions. These findings highlight that irrigation interval, beyond total irrigation amount, is an important management variable for optimizing cotton irrigation scheduling under water-limited conditions. The combined experimental and modeling framework provides practical guidance for irrigation design in arid regions.

Soil erosion, structural degradation, and inefficient nitrogen (N) use jointly constrain dryland agriculture on the Loess Plateau—a globally recognized ecologically fragile region. A common concern is that soil conservation practices may reduce short-term crop productivity. This study evaluated whether conservation tillage based on no-tillage and straw mulching, particularly when coupled with controlled-release N, could enhance soil aggregate stability, apparent nutrient availability, soybean productivity, and N-use efficiency. A two-year field experiment was conducted in 2022–2023 at the Shenmu Erosion and Environment Research Station, Shaanxi Province, China. Five treatments were compared: conventional tillage without N application (CTCK), conventional tillage with normal N application (CTU), conservation tillage without N application (SMCK), conservation tillage with normal N application (SMU), and conservation tillage with controlled-release N (SMS). SMS consistently increased the proportion of >0.25 mm water-stable macroaggregates, mean weight diameter, and geometric mean diameter. It also increased soil organic carbon and its particulate and mineral-associated fractions in the 0–30 cm profile, improved total N, mineral N, total P, and available P, and produced the highest soybean yield. Across two years, SMS yielded 1960.57 kg ha⁻¹, 162.26% higher than CTCK and 66.66% higher than CTU. The treatment also achieved the highest agronomic efficiency despite reduced N input. These findings indicate that integrating conservation tillage with controlled-release N can enhance soil structural stability, apparent nutrient availability, and soybean productivity. It confirms that soil conservation and high crop output are mutually reinforcing rather than conflicting. Given the ecological sensitivity of the Loess Plateau, this integrated strategy offers a promising pathway toward more resilient dryland farming systems.