Water and Nitrogen Dynamics in Drip Fertigated Tomato for Water of Different Qualities under Polyhouse Conditions

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.