Evaluation of macroscopic water extraction model for salinity and water stress in saffron yield production

Water scarcity and salinity are important limitations for saffron (Crocus sativus L.) production in arid and semi-arid regions. The purpose of this research was to study the interaction effects of water salinity and deficit irrigation on the macroscopic water extraction model for saffron. The effect of salinity and water stress on root-water uptake coefficient was determined by additive and multiplicative functions, and was compared with a recently purposed method. At every irrigation intervals, the root-water uptake coefficient α (h, ho) was reduced as the soil osmotic head (ho) decreased at higher salinity levels. Furthermore, the values of α (h, ho) were reduced at higher irrigation intervals. Root-water uptake coefficient was reduced by decreasing in soil matric head (h) and soil osmotic head at salinity levels greater than control. The results indicated that the additive and multiplicative functions for root-water uptake were not suitable for prediction of root-water uptake coefficient of saffron to show the interaction effect of salinity and deficit irrigation on flower yield prediction. The Mass and Hoffman, and Homaee and Feddes multiplicative equations resulted acceptable estimation of α (h, ho). Furthermore, saffron flower yield was predicted by using Homaee and Feddes α (h, ho) and FAO transpiration reduction coefficient in production function presented by Stewart and his colleagues. Results indicated that the FAO method did not predict the flower yield properly, specially in high irrigation intervals and high salinity levels, but the Homaee and Feddes
α (h, ho) resulted in acceptable prediction of the saffron flower yield with a minimum error at salinity and water stress treatments with relative yield of greater than about 40%. Therefore, Homaee and Feddes equation is recommended for estimation of α (h, ho) and flower yield of saffron.