Journal of Agricultural Engineering

Understanding of water and nitrogen (NO₃-N) dynamics within the crop root zone is important in devising efficient nitrogen management and environmental protection strategies. Field measurement on water and nutrient movements supported with modelling studies have been widely used to predict the water and NO₃-N distribution in the crop root zone. The objective of this study was to simulate the water and NO₃-N distribution in the soil under drip fertigated tomato irrigated with water of different qualities under polyhouse conditions. Field data were collected on spatial and temporal distribution of water and available NO₃-N during growing season. HYDRUS-2D model was calibrated and validated for simulating the water and NO₃-N distribution in crop root zone using coefficient of determination (R²), root mean square error (RMSE), index of agreement, and Nash-Sutcliffe model efficiency (NSE) as model performance indicators. The R² for calibration and validation period ranged from 0.70 to 0.99 for water distribution, and 0.70 to 0.96 for NO₃-N distribution implying that observed and predicted values were highly correlated. The value of RMSE ranged from 0.004 to 0.0016 cm.cm-3 for water, and 0.002-0.006 mg.ml^-1 for NO₃-N distribution. The index of agreement value varied from 0.86-0.98 for water distribution, and 0.89-0.99 for NO₃-N distribution. The lower values of NSE (0.17) represented less satisfactory performance, whereas higher values (0.98) for water distribution represented best fit of the observed and predicted values; and (-) 0.09 indicated that the mean observed NO₃-N content offered a better predictor than the model. The NSE value of 0.94 for NO₃-N distribution, showed that HYDRUS-2D demonstrated acceptable level of accuracy in NO₃-N prediction. The study concluded that the HYDRUS model performed well for predicting the water and NO₃-N distribution in tomato crop irrigated with water of different qualities under polyhouse conditions.