Evaluation of wheat water uptake reduction functions under conjunctive salinity and water stress conditions in Birjand

There are various mathematical water uptake models for simulating plants response to combined effects of drought and salinity stress. The reduction functions are classified as additive, multiplicative and conceptual models. As transpiration is the largest component of the agricultural water budget in arid systems, the efficacy of the simulation models depend on their ability to predict transpiration. In this study 6 different macroscopic reduction functions, namely; van Genuchten (additive and multiplicative), Dirksen et al., van Dam et al, Skaggs et al and Homaee were evaluated. The experiments were carried out on wheat crop in a factorial split plot design with 3 replicates. The treatments consist of four levels of irrigation (50, 75, 100 and 120%of crop water requirement), and three water qualities (1.4, 4.5, 9.6 dS/m). The result indicated that the crop response to drought and salinity stress was multiplicative at high salinity. Among multiplicative models, reduction function of Skaggs et al models provided better fitness to measured data than the other functions.