Modelling phosphorus and potassium dynamics in drip-irrigated potato systems using coupled agro-hydrological model

Efficient phosphorus (P) and potassium (K) management in drip-irrigated systems is vital for sustainable agriculture in arid and semi-arid regions, yet their dynamics are less understood. This study combined field experiments with coupled DSSAT and HYDRUS-2D models to investigate P and K behavior in drip-fertigated potato systems under semi-arid conditions. Field data, including soil water content, nutrient distribution, and crop growth were used to calibrate and validate the models for water flow, P and K dynamics. The HYDRUS-2D model was first calibrated and validated for soil water flow using measured water content data. Subsequently, the solute transport module was calibrated against observed soluble P and K concentrations and validated against independent measurements of available P and K. Results showed that K (≤15 cm) and P (≤13 cm) exhibited limited vertical mobility due to strong soil adsorption, while K showed greater lateral movement (≤35 cm) with minimal leaching. Sensitivity analysis identified soil hydraulic properties—especially saturated water content and pore-size distribution—and dispersion coefficients as major drivers of water and solute transport. Simulations aligned well with observed data (RMSE <0.05 cm³ cm−3 for water content; r² >0.8 for solutes), confirming the model’s reliability. Scenario analysis simulations indicated that splitting fertigation into four smaller applications, instead of two large doses, enhanced nutrient availability by 30–40 %, reduced peak fixation and leaching, and maintained tuber yield (30.2–31.5 t ha−1). Increasing irrigation water application by 1.5 times did not change vertical and lateral K and P movements. Overall, frequent, low-concentration fertigation improved nutrient uptake efficiency by 15–20 % and minimized environmental losses. This integrated agro-hydrological modelling approach offers practical insights for precision nutrient and water management, aligning with the United Nations Sustainable Development Goals (SDGs) for food security and resource conservation.