Application of DAYCENT to Access Long-Term Effect of a Water Resource Policy and Increasing Temperature on a Semi-Arid Pasture in South Central Oregon

Looking at anticipated global issues (e.g. climate change and food shortage), water resource management in arid and semi-arid regions needs to be designed not only to save water but also to maintain productivity and sustainability of agroecosystems. The CENTURY/DAYCENT ecological model can be used to simulate long-term effects of changes in water resource management and climate on agroecosystems. This study used CENTURY/DAYCENT with a new water flow submodel, which was calibrated for a semi-arid pasture with loam (KLL) and sandy loam (KLS) soils in south central Oregon, to simulate long-term effects of a water resource policy (converting flood irrigated pasture to non-irrigated pasture) and moderately increasing air temperature (4.0 degree Celsius/century) on site sustainability. Simulation results indicate significant soil organic matter (SOM) accumulation under irrigated pasture conditions established since the reclamation in late 1800’s of the native shrub/grassland (173.0 and 48.0 % at KLL and KLS, respectively). Our study suggests that SOM at KLL and KLS could be reduced by a conversion to non-irrigation pasture (36.9 and 34.4 %, respectively) and by increasing air temperature (9.5 and 10.0 %, respectively). These results suggest that it is important to take into account possible adverse effects associated with water saving policies in the changing environment to shape socially and environmentally sound water resource management decisions, and that our new version of DAYCENT can be a useful decision support tool.