Modeling the Projected Impacts of Mustard Cover Crops on Soil Water Content and Maize growth in Southwest Texas

Mustard grown as a cover crop retains root zone soil water content (SWC); however, if terminated late, it may lead to excessive water uptake. To test this, we analyzed seven global climate models (GCMs) together with the Decision Support System for Agrotechnology Transfer (DSSAT) to predict the effect of the projected climates on mustard and maize SWC, leaf area index (LAI), aboveground biomass (AGB), and yield in Southwest Texas. GCM drove these predictions in CROPGRO. Our study 1) developed a methodology to predict temporal variations in SWC, 2) calibrated the model and validated it against measured data, and 3) examined the quantity of inputs required for SWC predictions. Results show that mustard retained SWC (0.29-0.38 m3 m-3) only in future scenarios with moderate to high rainfalls. SWC (0.13-0.19) significantly decreased in scenarios where rainfall declined to lower levels. In 2019, simulated SWC for mustard was initially lower than observed but later aligned with it at midseason, indicating effective parameterization of infiltration and evapotranspiration (RMSE = 0.04). In 2020, simulated values of soil moisture closely matched observed ones at the 10 cm depth, although slight underestimations revealed the model’s sensitivity to variations in soil water in root zone. Model simulated LAI well for maize (RMSE = 0.1) and mustard (MAE = 0.1), and AGB for maize (RMSE = 1416.7 kg ha-1) and mustard (MAE = 149.2 kg ha-1; RMSE = 159.2). Under wet conditions, mustard retained soil moisture, supported maize growth, and boosted yield; under dry conditions, its effect was neutral.