A Coupled AquaCrop–Richards Model for Improved Crop Yield Prediction Through Physically Based Soil Water Dynamics

Abstract

Crop modelling is essential for agricultural water management but often relies on simplified water balance routines that limit representation of soil moisture dynamics. To address this limitation, we developed a coupled model that integrates the 1‐D Richards equation, solved using a finite difference method into the FAO AquaCrop. The coupled model was calibrated and validated using soil moisture, canopy cover, above‐ground biomass and seed cotton yield data from field experiments in the southeastern United States. Compared with hourly field measurements of soil moisture, AquaCrop–Richards achieved an average root mean square error (RMSE) of 0.023 m 3  m −3 across three soil depths over the growing season. Model performance for canopy cover, biomass and yield resulted in RMSE values of 12.18%, 1.77 t ha −1 and 0.96 t ha −1 , respectively, against observations. Under fully irrigated conditions, both models produced statistically indistinguishable yield estimates. However, under rainfed conditions, AquaCrop simulated 15.5% higher yields than AquaCrop–Richards. Analysis showed that AquaCrop produced rapid stepwise drainage, resulting in root‐zone water content 33%–37% lower than the coupled model. This reduced soil moisture triggered earlier water stress which led to yield overestimation. These results indicate that AquaCrop‐Richards improves soil moisture representation and is robust under water‐limited conditions.