Modelling soil water and maize growth dynamics influenced by shallow groundwater conditions in the Sorraia Valley region, Portugal

The southern European region faces increasing pressure on fresh water resources due to economic development and climate change. Integrative modelling operational tools capable of simulating the full soil-water-atmosphere transfer system are needed to improve agricultural water management at the plot scale. In this study, the MOHID-Land model was used to simulate soil water dynamics and maize growth in a plot located in the Sorraia Valley region, southern Portugal, during the 2014 and 2015 growing seasons. The simulated crop parameters included the leaf area index, canopy height, aboveground biomass, and maize yields. A system-dependent boundary condition that triggered irrigation when a certain threshold pressure head (h_t) was reached in the root zone domain was also implemented in MOHID-Land. This boundary condition was used to optimize the irrigation scheduling practices in scenarios with different groundwater depths and h_t values. MOHID-Land successfully simulated soil water contents and crop growth during the monitored crop seasons, producing acceptable errors of the estimates after normalization (0.061 ≤ NRMSE ≤ 0.390), and relatively high modelling efficiencies (0.11 ≤ EF ≤ 0.94). Model simulations further showed the importance of capillary rise (CR) to the soil water balance, and confirmed the inefficient water use of current irrigation practices. The analyses of the irrigation scenarios showed an increase of CR from 17.7 to 66.9% of the actual evapotranspiration values after optimizing the irrigation scheduling practices, and the contribution of the shallow groundwater to the root zone. Water productivity also increased up to 12% when compared with the farmer's standard irrigation practices. The MOHID-Land model proved to be an effective tool for irrigation water management in the Sorraia Valley region.