A Water-Balance, Climate Model for Range Herbage Production

A crop production model was modified and evaluated for application to native grassland ecosystems. The model effectively predicted annual herbage production for range sites near Sidney, Montana, and Mandan, North Dakota, where model-predicted yields were within 10% of field measured yields for 12 of the 15 test years. Soil water content, as calculated by the model, was also closely correlated (r2=0.91) with field measured soil water. Model inputs include beginning soil water content, daily precipitation, and an estimate of potential evapotranspiration. Soil water content, evaporation, and transpiration are calculated daily. Yields are determined as a function of the actual to potential transpiration ratio. Availability of input data, relative simplicity, and low computer costs make this model a viable tool for both research and resource management.