A model for assessing crop response to salinity

CropSyst, a management-oriented crop growth model, was modified to assess c rop response to salinity. The effect of salinity was included in the existi ng water uptake module by adding an osmotic component to the soil water pot ential and developing a function to account for salinity effects on root pe rmeability. The effect of salinity on water uptake is the link to simulate crop growth reduction. A qualitative analysis showed that the model simulat ed expected trends of crop response to salinity as affected by cultivar tol erance, atmospheric vapor pressure deficit, and soil water availability. Co mparisons with data from sprinkler line experiments were performed for barl ey grown at Zaragoza (Spain) in 1986 and 1989, nd corn at Davis, Calif. and Fort Collins, Cole. in 1975. These experiments included different salinity and irrigation levels. At Davis, the model simulated well the effect of sa linity/irrigation treatments on water use, biomass, and crop yield, with va lues for the Willmot index of agreement (d) generally better than 0.94 (a v alue of 1.0 implying perfect agreement). At Fort Collins, simulation of gra in yield was less satisfactory (d fluctuated between 0.83 and 0.90), but th e agreement was good for crop water use and biomass (d generally better tha n 0.96). The lower performance for grain yield was attributed to large and erratic variations in the observed harvest index. The agreement between sim ulated and observed values tended to be lower at Zaragoza, with d values fl uctuating between 0.84 and 0.91 for biomass and yield in the 2 years includ ed in this evaluation. Unusually high measured yields in 1989 and erratic v ariation in 1986 were attributed to small sample size. The small size (incr eased measurement error) of samples typically obtained in sprinkler line so urce experiments tends to limit their use for evaluation of simulation mode ls.