LAUSR

Abstract The AquaCrop model was evaluated considering a data set from a cowpea (BR3-Tracuateua cultivar) cultivation in Castanhal/Brazil under different irrigations during the reproductive phase, which is sensitive to water deficit. Data on leaf area index (LAI), soil water content (SWC), biomass, and final yield of two harvests were used for model calibration (2013) and validation (2014). LAI data were used for parameterization of canopy cover (CC), and some crop parameters obtained in the field. The model was also used to evaluate the impacts of sowing dates, as well as the strategy of using an economical irrigation threshold (60% of Readily Available Water) on the water use and crop yield. Regarding the results after parameterization of the canopy cover curve, the model efficiency index (EF) presented a satisfactory performance (0.98), which is due to the high correlation coefficient (R2 = 0.99) between the simulated and observed values and the low values of normalized root mean square error (NRMSE 0.70) for all treatments, with low estimated errors and NRMSE representing 8.12% of mean SWC observations during validation, indicating high precision for simulation of biomass and cowpea yield. The model performance index ranged from 0.92 to 0.94 for biomass and from 0.92 to 0.99 for final yield. These results showed that AquaCrop is suitable for simulating biomass production and yield of cowpea. Additionally, sowing in early April is appropriate for better water use and productivity and the tested irrigation threshold can be indicated to significantly improve final crop yields.