Evaluating Water Uptake Reduction Functions under Salinity and Water Stress Conditions

Use of deficit irrigation to conserve water by minimizing leaching fraction during an irrigation season, or even across several irrigation seasons causes salt accumulate within the root zone. Naturally, salinization of the root zone is exacerbated when marginal waters are used. In this situation plants are experiencing simultaneously drought and salinity stress. Various mathematical models are exist for plants response to combined drought and salinity stress and its corporation in water uptake. The reduction functions are classified as additive, multiplicative and non coseptive models. Because transpiration is the largest component of the water budget in arid systems, the efficacy of models to simulate water and salt movement is depended on their ability to predict transpiration. In this study six different macroscopic reduction functions; Van Genuchten (additive and multiplicative), Dirksen et al., Van Dam et al, Skaggs et al and Homaee were evaluated in greenhouse condition using tomato data were exerted. This experiment was performed based on completely randomized design with three replicates and eight levels of salinity (0.75, 1.5, 2.5, 3.5, 4.5, 6, 8 and 10 dS/m) .Drought levels carry out as matrix potential during the experiment. The result of this study indicated that without salinity stress, all reduction function have a good agreement with measured data. Also, The result of this study indicated that the crop response to drought and salinity stress is additive low salinity level and is multiplicative at salinity level above 3.5 dS/m. among multi model, reduction function of Skaggs et al and Homaee's models were better fitness to measured data than the other functions.