Evaluation of FAO aquacrop model for ability to simulate attainable yields and water use for field tomatoes grown under deficit irrigation in Harare, Zimbabwe

Crop simulation models have an important role in evaluating irrigation management strategies for improving agricultural water use. The aim of this study was to evaluate the AquaCrop model for ability to simulate water use and tomato (Lycopersicon esculentum Mill.) fruit yields under deficit irrigation conditions. A fieldexperiment was conducted at Thornpark, University of Zimbabwe Research site over four seasons (2014 and 2017). The data collected for yield and water use were used to run and evaluate the performance of AquaCrop in predicting water use efficiency and fruit yield. Four treatments defined in relation to 100% of the crop water requirement (ETc) were simulated: T1 100% ETc; T2 80% ETc; T3 60% ETc and T4 50% ETc. The model performance was satisfactory, with a good correlation between the simulated and observed soil water content (SWC) and fruit yield (FY). All the statistical indicators (The Normalised Root Mean Square Error (R2), Root Mean Square Error (RMSE), Nush Sutcliffe Model Efficiency (EF), Pearson Correlation Coefficient (r), and Willmott’s Index of Agreement (d)) used to compare the observed and predicted parameters, showed good performance; for example the EF showed values of 0.91 for SWC, the (r) showed values of 0.95 for SWC and a FY of 2.79 and 2.39 metric tonnes ha-1 for the simulated results. The results showed that the values of the simulated FY were consistent with the measured, with corresponding coefficients of determination (R2) of 0.93. The results revealed AquaCropisable to simulate the yield of tomato and the seasonal water requirements to an appreciable degree. However, it must be pointed out that the calibration of AquaCrop suffered from lack of measured data on the progress of crop canopy cover, which is an important parameter used in developing the model. The results obtained showed that AquaCrop can be used effectively in simulating tomato production under deficit irrigation and, therefore, it can be used as a decisionmaking tool for irrigation management of tomatoes in Zimbabwe.