Predicting maize transpiration,water use and productivity for developing improved supplemental irrigation schedules in western uruguay to cope with climate variability

Abstract

Various maize irrigation treatments including full and deficit irrigation were used to calibrate and validate the soil water balance and irrigation scheduling model SIMDualKc at Paysandú, western Uruguay. The model adopts the dual crop coefficient approach to partition actual evapotranspiration (ETc act) into actual transpiration (Tc act) and soil evaporation (Es). Low errors of estimation were obtained for simulating soil water content (Root mean square errors (RMSE) ≤ 0.014 cm3·cm-3 with calibrated parameters, and RMSE ≤ 0.023 cm3·cm-3 with default parameters). The ratio Es/Tc act ranged from 26% to 33% and Es/ETc act varied from 20% to 25%, with higher values when the crop was stressed offering less soil coverage. Due to rainfall regime, runoff and deep percolation were quite large. The Stewarts phasic model was tested and used to predict maize yield from Tc act with acceptable errors, in the range of those reported in literature. Water productivity values were high, ranging 1.39 to 2.17 kg·m-3 and 1.75 to 2.55 kg·m-3 when considering total water use and crop ET, respectively. Using a 22-year climatic data series, rainfed maize was assessed with poor results for nearly 40% of the years. Differently, alternative supplemental irrigation schedules assessed for the dry and very dry years have shown good results, particularly for mild deficit irrigation. Overall, results show appropriateness for using SIMDualKc to support the irrigation practice.