Field Evaluation of Water Uptake Models Under Conjunctive Salinity and Water Stress Conditions in Semi-dry Region by Wheat (Case study: Birjand)

In order to evaluate the efficiency of six different macroscopic water uptake functions, consisted of additive (M1), multiplicative (M2, M3 and M4) and conceptual (M5 and M6) models using field data of Ghods cultivar of wheat under salinity and drought stress, a study was conducted in the research field of university of Birjand during 2005-06 in split plots design based on randomized complete blocks (RCBD) with three replications. In this study, the main plots consisted of different levels of salinity (1.4, 4.5 and 9.6 ds m-1) and sub plots consisted of four levels of irrigation (50, 75, 100 and 120 percent of crop water requirement). The results showed that the additive model (M1) estimated yield less than actual amount. In other word, the effect of combined stresses on wheat yield was less than the one as compared to summation effects of salinity and water stress. The effect of drought stress on reduction of yield was more than salinity stress. The results also revealed that reduction functions of M6 and M5 models were better fitness to measured data than the other functions. The results revealed that M6 model estimated the reduction of relative yield of wheat under simultaneous stresses conditions of salinity and drought better than other models ( RMSD=0.17), although the M5 model also had acceptable accuracy (RMSD = 0.22).