Assessing potato transpiration, yield and water productivity under various water regimes and planting dates using the FAO dual Kc approach

Two years of experimental field data on potato (var. Spunta) were used to calibrate and validate the SIMDualKc model. This model adopts the FAO dual Kc approach that provides the partition of crop evapotranspiration into crop transpiration and soil evaporation. Results of model calibration show a good agreement between soil water observations and predictions, with low errors of estimate - RMSE <3.7% of the mean observed soil water - and high modelling efficiency (>0.87). The calibrated basal crop coefficients for the initial stage, mid-season and end of season are 0.15, 1.10 and 0.35, respectively. After model calibration, the crop transpiration simulations were used to derive the yield response factor (Ky = 1.09). Coupling SIMDualKc with the Stewart's model provided for a good prediction of yields, with NRMSE lower than 8%. Irrigation scheduling scenarios were simulated with SIMDualKc model for various planting dates and limited stress conditions. Related results have shown that anticipating planting dates to the second half of February could lead to less irrigation requirements, higher yields and better water productivity relative to consumptive water use (WPET), crop transpiration (WPT) and seasonal water use (WPWU). These WP indicators were useful comparators. Contrarily, the WP relative to season irrigation depths (WPIrrig) showed a great variation among scenarios and a tendency to be higher when deficit irrigation was applied, which contradicts the objectives of farmers in terms of obtaining high yields and economic returns. The model and methodologies used were adequate to support irrigation management advising for farmers.