Evaluating Water Uptake Reduction Functions under Salinity and Water Stress Conditions in Pepper (Capsicum Annuum)

Various mathematical models are available for estimating the response of plants to combined drought and salinity stress and the share of each component in water uptake. The reduction functions are classified as additive, multiplicative, and conceptual models. In this study, 5 different macroscopic reduction functions, namely, Van Genuchten (additive and multiplicative), Dirksen et al., Van Dam et al, and Homaee, were evaluated in greenhouse conditions using pepper data. This experiment was performed based on a completely randomized design with 3 replicates and 3 levels of salinity (2.5, 4.5, and 6.5 dS/m). Drought levels were carried out as matric potential during the experiment at 3 levels (50%, 60%, and 70% of field capacity). The results of this study indicated that the crop response to drought and salinity stress was additive at low salinity level (2.5 dS/m) and multiplicative at 4.5 and 6.5 dS/m salinity levels. Also, reduction function of Van Genuchten (average RMSE=3%, ME=0.15) had the best fit at low salinity level (2.5 dS/m). Among the multiplicative models, reduction functions of Dirksen model at 4.5 dS/m with average RMSE=5% and ME=0.09 was in better fit to the measured data than the other functions.Homaee (average RMSE=9%, ME=0.12) and Vandam models (average RMSE=9%, ME=0.11) at higher salinity level (6.5 ds/m) were in better fit to the measured data than the other functions.