Simulation of soil water and nitrate transport in a wheat field under various nitrogen fertilizer rates and rainfed conditions using HYDRUS-1D

Abstract

In this study, we used HYDRUS-1D software to simulate soil water and nitrate (NO3-N) transport in a rainfed wheat field under various nitrogen (N) fertilizer scenarios (0 to 126 kg ha–1) in Morocco. We used inverse modeling to calibrate the input parameters involved in the simulation. The comparison between simulated and measured soil water (SWC) and NO3-N contents at different soil layers was carried out using the index of agreement (d), determination coefficient (R2), RMSE, and MAE. By considering the soil profile (0–100 cm), acceptable SWC simulation accuracies were obtained for the calibration and validation steps (d=0.88–0.94, R2=0.67 to 0.80, RMSE=0.034–0.051 cm3cm–3, and MAE=0.024–0.038 cm3cm–3), while NO3-N simulation was less accurate (d=0.49–0.82, R2=0.20–0.58, RMSE=0.015–0.068 mg cm–3, and MAE=0.012–0.046 mg cm–3). In addition, the observed NO3-N contents showed a lack of significant differences in the root zone (20–100 cm) between N fertilizer rates (p>0.05), which was consistent with the lack of N fertilizer effects on simulated NO3-N leaching below the soil profile by HYDRUS-1D. The NO3-N leached amount accounted for 25 kg ha–1 and was derived mainly from the initial soil N contents. The simulated N balance of the soil profile revealed that volatilization and denitrification were the major pathways of N fertilizer loss, accounting for about 3.8 and 51.7% of the N fertilizer rates, respectively. We suggest further studies to improve the simulation accuracies of HYDRUS-1D using sufficient calibration data from long-term wheat experiments to ensure effective N fertilization management in the study area.