Evaluation of Water Uptake Functions under Simultaneous Salinity and Water Stress Conditions in Turf Grass

A significant part of Iran lays in arid and semi-arid regions، that face with drought and salinity. In other hand، Water use efficiency under this condition is generally low. Mathematical models that simulate transpiration of plant as a function of soil moisture availability are useful tools for water productivity management. Various mathematical models have developed to estimate transpiration of plant reduction due to combined effect of drought and salinity stresses. This study compares six different macroscopic reduction functions; namely: Van Genuchten (additive and multiplicative، 1987)، Dirksen & Augustijn (1993)، Van Dam et al. (1997)، Homaee (1999) and Skaggs et al. (2006). These models were evaluated against measured transpiration of turfgrass (Lolium prenne) in greenhouse environment for 12 treatments. The factorial experiment was performed based oncompletly randomized design with four levels of salinity (0. 5، 5. 5، 7. 5 and 10 dS/m) and three levels of drought (water refills of 100، 75 and 50 %FC) and three replicates for each treatment. The results indicated that the crop response to water and salinity stresses is additive in low salinity level and is multiplicative at salinity level above 5. 5 dS/m. Among used models، reduction functions of Skaggs et al، Homaee and Van Genuchtenshowed better agreement with the measured data.