SALINITY, WATER-USE AND YIELD OF MAIZE - TESTING OF THE MATHEMATICAL-MODEL ECOSYS

There is a need to establish how root water uptake should be calculated under saline conditions, and to test calculated uptake against experimental data recorded under documented site conditions. In this study, the ecosystem simulation model ecosys was expanded to include an ion transfer-equilibrium-exchange model used to calculated electrical conductivity and osmotic potential. This expanded model was tested against experimental data for maize growth and water use reported under different irrigation and salinity levels at four different sites in the western U.S. to determine if salinity effects on crop growth and water use could be modelled from the effects of salinity on soil osmotic potential. The model was able to reproduce reductions in water use and phytomass yields on salinized (10 g total salts kg(-1) water) soils that ranged from 10 to 50% of those on non-salinized controls. In general, these reductions increased with increasing irrigation deficits. These reductions arose in the model from reduced canopy water potentials and conductances caused by reduced osmotic potentials in the saline soils. The hypothesis that salinity effects on crop growth and water use are caused by salinity effects on soil osmotic potential appear to be supported under the range of conditions included in this study. Models such as ecosys that are based on general hypotheses for the effects of salinity upon biological activity may be well adapted for general use in assessing the effects of salinity on crop growth and water use with different soils, managements and climates.