Performance Evaluation of the AquaCrop Semi-quantitative Method for Prediction of Radish Growth under Different Levels of Nitrogen Fertilizer

In this research, the performance of semi-quantitative method in AquaCrop model for prediction of biomass and vegetation under various nitrogen fertilizer managements was evaluated by comparing the simulated parameters with the measured results in the greenhouse. The radish cherrybel cultivar was cultivated in the greenhouse of Pardis Aburaihan, University of Tehran without thermal and water stress during two periods (February 2018 and April 2018). The experiment was conducted as a randomized complete block design with different treatments such as zero fertilizer as control (N0), 50 (N1), 100 (N2), 150 (N3), 200 (N4), 250 kg nitrogen per hectare (N5), using Urea fertilizer with three replications. N0 and N3 treatment data of the first cultivation period were used for calibration and the other data were applied for model validation. Relative Root Mean Square Error (RRMSE), Determination Coefficient (R2) and Mean Bios Error (MBE) were used to evaluate the performance of model. The values of these parameters (RRMSE, R2 and MBE) for biomass simulation were 11.12%, 0.973, 0.032 ton.ha-1, respectively for N0 and 10.32%, 0.975, and -0.002 ton.ha-1, respectively for N3 in the calibration step. These parameters for canopy cover simulation were 15.93%, 0.884 and 4.30%, respectively for N0 and 12.84%, 0.916 and 5.94%, respectively for N3 in the calibration step. Also, in the validation step, the range of changes in these parameters for biomass simulation were 13.7-25.7%, 0.923-0.988, -0.110-0.118 ton.ha-1 and for canopy cover simulation were 19-25.4%, 0.768-0.867, 5.7-10.18%, respectively. Based on the results, AquaCrop model simulated the biomass and canopy cover precisely under different levels of nitrogen fertilizer and during the growing period.