Modeling the Projected Climate Change Impacts on Soil Water Content for Mustard and Maize Crop Rotation in Southwest Texas

Abstract Mustard ( Brassica spp .) grown as a cover crop retains root-zone soil water; however, if terminated late, it may lead to excessive water uptake. We calibrated and evaluated the decision support system for agrotechnology transfer (DSSAT) using field data from 2019-20 to simulate soil water content (SWC), leaf area index (LAI), aboveground biomass (AGB), and grain yield for maize ( Zea mays L.) in Southwest Texas. We applied DSSAT with climate projections from seven global climate models (GCMs) to assess soil water dynamics and crop responses under projected climate scenarios. The model performed well, accurately calibrating and evaluating LAI for maize (RMSE = 0.28) and mustard (RMSE = 1.42), and AGB for maize (RMSE = 1092.51 kg ha ⁻ ¹ ) and mustard (RMSE = 772.54 kg ha ⁻ ¹ ). Simulated SWC matched observed values at midseason in 2019 (RMSE = 0.04) and closely followed field observations at 10 cm depth in 2020, confirming the model's sensitivity to root-zone moisture dynamics. Economic returns in 2020 rose by 12% over 2019 due to favorable climate conditions. Future climate impacts were assessed using DSSAT’s Seasonal Analysis tool with bias-corrected projections from seven GCMs under RCP 4.5 and RCP 8.5. Results showed that maize yield peaked in 2050 under RCP 4.5 and declined sharply by 2070 under RCP 8.5. Mustard cover cropping improved SWC (0.29 m ³ m ⁻ ³ ) and improved maize yield under moderate to high rainfall scenarios, but had neutral effects under drier conditions (SWC as 0.13 m ³ m ⁻ ³ ). The study highlights that maintaining SWC above 0.27 m ³ m ⁻ ³ is critical for maize yield stability in this region. Projected maize irrigation demand will increase 20% by 2100. Sensitivity analysis showed that maize yield is strongly influenced by genetic parameters P1, P5, and G2 that regulate phenology and grain filling duration. Our study recommends deficit subsurface drip irrigation with focused irrigation at both flowering and physiological maturity stages to maximize water use efficiency (WUE) and economic returns to sustain maize-mustard production in semi-arid regions under future climate conditions. Our study contributes to the understanding of SWC in mustard-maize rotation system.