Simulating the Yield Response of Orange Fleshed Sweet Potato 'Isondlo' to Water Stress Using the FAO AquaCrop Model

Research trials that evaluated response of orange fleshed sweet potato to three irrigation treatments were carried out on a sandy loam soil under a rain shelter at ARC-Roodeplaat Vegetable and Ornamental Plant Institute, Republic of South Africa. The crops were irrigated using a sprinkler irrigation system in the summer season of 2008/09 and 2009/10. Meteorological records, soil water content, crop growth measurements, biomass production and final harvestable yield were collected and used to calibrate the FAO AquaCrop model. Calibration was done using the data collected in 2008/09 and the model was tested against independent data sets collected in 2009/10. The model predicted biomass, canopy cover and the harvestable yield for both stressed and non-stressed treatments reasonably well. Crops irrigated at full irrigation gave higher biomass and harvestable yield compared to the water stressed treatments. Correlation coefficients (r(2)) of 0.92 and 0.96 were found between measured and predicted values for canopy cover and biomass production. The agreement of observed and simulated values of biomass was relatively good for the low irrigated treatments (30FC). The model overestimated for the medium irrigated treatments (60FC). This suggests that the model could be used, by refining the parameters, to simulate different irrigation scenarios for decision making in irrigation schemes in South Africa. The effect of different irrigation management scenarios was also simulated to evaluate the effect of water stress on yield and biomass production. A decline in total root yield due to water stress was simulated; with a tendency of yield drop when the crop was subjected to water stress later in the growing season. For successful orange fleshed sweet potato production, irrigation management that stresses the crop for a short period of time without compromising water productivity and yield should be preferred.