The dual Kc approach to assess maize and sweet sorghum transpiration and soil evaporation under saline conditions: Application of the SIMDualKc model

Soil salinization is an increasing threat in agricultural water scarce regions, where even saline irrigation waters can be seen as an important resource. The sustainable use of these waters requires a precise knowledge of the processes involved, with modeling assuming a critical role in irrigation water management. The objective of this study was to develop and test an empirical approach for considering the effect of transient salinity stress on maize and sweet sorghum transpiration rates estimated by the SIMDualKc model. This approach took into account the soil salinity status given by the electrical conductivity of the soil saturation extract (ECe) at the beginning and at the end of each growing season, crop tolerance to soil salinity (ECethreshold and b), and soil water availability under saline condition. Model simulations of soil water content (SWC) were compared with field observations, while estimates of actual crop evapotranspiration (ETcact) and crop transpiration (Tcact) were compared with those computed with HYDRUS-1D. SIMDualKc successfully simulated SWC in plots irrigated with fresh and synthetic saline waters, producing a regression coefficient (b0) close to 1, a root mean square error (RMSE) below 0.012 m3 m−3, and a modeling efficiency (EF) above 0.80. SIMDualKc estimates of the ETcact/ETc and Tcact/Tc ratios for maize and sweet sorghum showed a seasonal reduction of the potential values up to 0.16 and 0.36, respectively, due to salinity stress, and were relatively close to those given by HYDRUS-1D using a more complex physically-based approach. SIMDualKc estimates may thus be considered reliable, with this model becoming a simple alternative tool for saline irrigation management in water scarce regions.