A team of researchers from Oak Ridge National Laboratory and Dartmouth College have compiled national data on switchgrass yield as it relates to site location, plot size, stand age, harvest frequency, fertilizer application, climate, and land quality. Their paper appears in the July-August 2010 Agronomy Journal, published by the American Society of Agronomy.
The scientists compiled a total of 1,190 biomass yield observations for both lowland and upland types of switchgrass grown from 39 field sites across the United States. Observations were pulled from 18 publications that reported results from field trials in 17 states, from Beeville, TX in the south, to Munich, ND in the Midwest, and Rock Springs, PA in the northeast.
Statistical analysis revealed that much of the variation in yield could be accounted for by variation in growing season precipitation, annual temperature, nitrogen fertilization, and they type of switchgrass.
Lowland switchgrass outperformed upland varieties at most locations, except at northern latitudes. Annual yields averaged 12.9 metric tons per hectare for lowland and 8.7 metric tons for upland ecotypes. Some field sites in Alabama, Texas and Oklahoma reported biomass yields greater than 28 metric tons per hectare using the lowland cultivars Kanlow and Alamo.
The research team did not observe any bias for higher yields associated with experimental plot size, row spacing, or with preferential establishment of stands on high quality lands. A model developed from the data, based on long-term climate records, projected maximum yields in a corridor westward from the mid-Atlantic coast to Kansas and Oklahoma. Low precipitation west of the Great Plans limited yields in that region.
This is the largest data base analyzed to date for energy crop productivity as a function of geographically distributed variables. The finding that there is no bias with respect to either plot size or land productivity is important. A promising future direction is to apply the modeling approaches taken here to additional bioenergy crops at a global scale in combination with various land use scenarios.
—Lee Lynd, co-author on the article and Steering Committee Chair of the Global Sustainable Bioenergy Project
Scientists at Oak Ridge National Laboratory and Dartmouth College continue to explore factors involved in the production of biomass from switchgrass and other dedicated energy crops. One of the lessons learned from the current analysis is that yield data from an even broader range of soil and climatic conditions will be useful in building better predictive models. Future studies should extend the geographic distribution of field trials and thus improve the understanding of biomass production for promising biofuels like switchgrass.
The full article is available for no charge for 30 days.
S. D. Wullschleger, E. B. Davis, M. E. Borsuk, C. A. Gunderson and L. R. Lynd (2010 Biomass Production in Switchgrass across the United States: Database Description and Determinants of Yield. Agron J 102:1158-1168 doi: 10.2134/agronj2010.0087