A model for assessing crop response to salinity

Abstract.

CropSyst, a management-oriented crop growth model, was modified to assess crop response to salinity. The effect of salinity was included in the existing water uptake module by adding an osmotic component to the soil water potential and developing a function to account for salinity effects on root permeability. The effect of salinity on water uptake is the link to simulate crop growth reduction. A qualitative analysis showed that the model simulated expected trends of crop response to salinity as affected by cultivar tolerance, atmospheric vapor pressure deficit, and soil water availability. Comparisons with data from sprinkler line experiments were performed for barley grown at Zaragoza (Spain) in 1986 and 1989, and corn at Davis, Calif. and Fort Collins, Colo. in 1975. These experiments included different salinity and irrigation levels. At Davis, the model simulated well the effect of salinity/irrigation treatments on water use, biomass, and crop yield, with values for the Willmot index of agreement (d) generally better than 0.94 (a value of 1.0 implying perfect agreement). At Fort Collins, simulation of grain yield was less satisfactory (d fluctuated between 0.83 and 0.90), but the agreement was good for crop water use and biomass (d generally better than 0.96). The lower performance for grain yield was attributed to large and erratic variations in the observed harvest index. The agreement between simulated and observed values tended to be lower at Zaragoza, with d values fluctuating between 0.84 and 0.91 for biomass and yield in the 2 years included in this evaluation. Unusually high measured yields in 1989 and erratic variation in 1986 were attributed to small sample size. The small size (increased measurement error) of samples typically obtained in sprinkler line source experiments tends to limit their use for evaluation of simulation models.