Assessment of Perennial Grass Inventories Predicted in the Billion-Ton Studies

The U.S. Department of Energy (DOE) has estimated herbaceous biomass availability through simulations with the Policy Analysis System (POLYSYS) agricultural modeling framework. An operational assumption for POLYSYS limited conversion of pastureland to perennial grass crops to counties east of the 100th meridian as a proxy for precipitation sufficient for economically viable yield, but allowed cropland conversion regardless of location. Knowledge of local conditions raised questions about predicted biomass quantities for Texas counties in the 2011 assessment. POLYSYS was rerun with different assumptions, specifically replacing the 100th meridian boundary with annual average precipitation data and limiting cropland conversion in low-rainfall counties. Perennial grass production was found to be overestimated by 8% and 87% in the U.S. and Texas, respectively (at $66.14 DMg-1), when limiting all land conversion to regions with >635 mm precipitation. Total herbaceous biomass predicted was approximately the same as in the BT2, but the biomass geographical location changed across the nation. Texas' biomass contribution decreased from 6% to 1% at $66.14 DMg-1 and from 16% to 11% at $88.18 DMg-1. Subsequent to this research being conducted, the DOE released the 2016 biomass inventory assessment, and these results are compared to those newest estimates.