5. Calibration of AquaCrop Salinity Stress Parameters for Barley Under Different Irrigation Regimes in a Dry Environment

In the arid environment of southern Tunisia, FAO’s AquaCrop model version 4.0 has been calibrated to evaluate the effect of irrigation strategies with saline water on barley yield. Data sets during barley cropping seasons 2012 and 2013 in Médenine, southern Tunisia, were used to calibrate and evaluate this model. Barley canopy cover, grain yield, biomass production, and soil salinity and water content were simulated under three irrigation regimes. The RMSE, Willmott index of agreement (d), and r² analysis showed good agreement between the simulated and observed data, especially for the biomass production and grain yield. The difference between observed and simulated grain yield under full irrigation was only 1% for the first and second seasons. The difference for biomass was around 2%. The trend of canopy cover was well simulated with slight over estimation in the beginning of the season for both seasons. Salinity stress parameters were adjusted to simulate the combined effect of drought and salinity stress where the electrical conductivity of water (ECw) was used as the indicator threshold of salinity instead of the saturated soil-paste extract (ECe) in this case. The model tended to overestimate the soil water content and the ECe but with reasonable statistical indices for total root zone soil water content (RMSE: 8.6–11 mm, d: 0.78–0.98) and for ECe (RMSE: 1.35–0.94 dS/m, d: 0.63–0.88).