Scientists evaluate switchgrass yields across US

By Anna Austin
A team of scientists have released what they believe is the largest database available comparing energy crop yields in relation to variables such as site location, plot size, stand age, harvest frequency, fertilizer application, climate and land quality.

Oakridge National Laboratory and Dartmouth College researchers compiled 1,190 biomass yield observations for both lowland and upland types of switchgrass grown on 39 sites across the U.S. These observations were extracted from 18 publications that reported results from field trials in 17 states, from Texas to North Dakota to Pennsylvania.

Among the factors examined, researchers found that much of the differences in switchgrass yields could be accounted for by variation in growing season, precipitation, annual temperature, nitrogen fertilization and the type of switchgrass grown in a specific region.

For example, lowland switchgrass outperformed upland varieties at most locations, except at northern latitudes. Annual yields averaged 12.9 metric tons (14.2 tons) per hectare (2.47 acres) 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.

Overall, researchers also found that yields were relatively consistent with the natural geographic range of switchgrass, although significant yields were predicted along the Pacific Coast states. Yields were shown to be limited by precipitation west of the Great Plains and, to a lesser extent, by low mean annual temperature. Maximum switchgrass biomass yields were projected westward from the mid-Atlantic Coast region to Kansas and Oklahoma.

Stan Wullschleger, crop physiologist who led the study, noted that field trials are often planted to provide local estimates of crop production. "However, viewed in a broader context, results from individual field trials can contribute to a larger perspective and provide regional- to national-scale estimates of yield and the variables that determine that yield," he said.

The researchers concluded that future studies should extend the geographic distribution of field trials and thus improve understanding of biomass production as a function of soil, climate and crop management for promising biofuel feedstocks.
The paper was published by the American Society of Agronomy in the July-August 2010 Agronomy Journal. It can be accessed at