Modeling Nitrogen Dynamics in Maize under Drip Fertigation Using the HYDRUS Model: A Calibration and Validation Approach

Nutrient transport models simulate nutrient distribution in soil and help understand the relationship between nutrient application timing, crop uptake, yield, soil health, and groundwater pollution. Identifying a suitable model is crucial. A field experiment was conducted to model nitrogen dynamics using the HYDRUS-2D model in a split-plot design with three irrigation levels (0.6 ETc (I1), 0.8 ETc (I2), 1.0 ETc (I3)) and four nitrogen treatments (80% RDN (N1), 100% RDN (N2), 120% RDN (N3), and manual application (N4)) on sandy clay loam soil during kharif 2018, rabi 2018-19, and kharif 2019 at Dr N.T.R. College of Agricultural Engineering, Bapatla, Andhra Pradesh. The model was calibrated and validated for drip-fertigated maize. HYDRUS-2D uses Richard's equation for water flow and a non-equilibrium chemical transport model to simulate solute movement during transient flow in variably saturated porous media. The advection-dispersion equation was applied to simulate single non-reactive ion transport in a three-dimensional axi-symmetrical setup. Validation during kharif 2019 was done to simulate nitrogen concentration. Calibration results showed increased crop nitrogen uptake with higher N application from the development stage. Simulated and observed available nitrogen content up to 100 cm depth at 50 days after sowing (30 cm from emitter) showed good agreement, with R² = 0.981. Relative error ranged from -14.71% to -5.17%, averaging -8.62%. Root Mean Square Error (RMSE) was 0.103, and model efficiency was 0.98. Nitrogen availability was higher at 15 cm from the emitter. Therefore, HYDRUS can effectively simulate soil water and nutrient dynamics and is suitable for application in other crops and conditions.