Evaluating warm-season grass production in temperate-region pastures: A simulation approach

The pasture submodel of the Integrated Farm System Model (IFSM) was modified to simulate the biomass production and nutritive dynamics of a warm-season (C4) grass monoculture. Predictions of yield and nutritive value were calibrated and evaluated with 5 years of field data from grazed switchgrass (Panicum virgatum) pastures in Pennsylvania, USA. Uncertainty analysis of biomass at the beginning of each growth cycle showed that each estimated yield was sensitive to the amount of biomass that started its growth cycle but not to those of previous growth cycles. Sensitivity analysis showed that predicted yield was most sensitive to physiological parameters such as proportion of photosynthate partitioned to shoots, specific leaf area, structural growth per unit carbohydrate, leaf photosynthetic efficiency, and the light extinction coefficient.