Assessing Carbon Impacts of Land-Use Choices for Bioenergy Crops

Researchers considered five contrasting scenarios for subsequent management.

The Science

The Conservation Reserve Program (CRP) contains over 13 million hectares of former croplands now in grasslands, providing a reservoir of biodiversity, water quality, and carbon sequestration benefits. However, these benefits could be lost if the land is converted back to agricultural use for biofuel production. Scientists from the DOE Great Lakes Bioenergy Research Center analyzed the effects that converting CRP lands to annual crops for biofuel production (continuous corn and corn-soybean rotation, each either tilled or permanent no-till) would have on greenhouse gas (GHG) emissions as compared with directly harvesting perennial grasses on these lands for cellulosic ethanol. They report that although a no-till management regime of an annual bioenergy crop would reduce the carbon debt significantly compared with tilling, harvesting perennial grasses would result in virtually no GHGs lost, because the disruption required when converting to annual crops would be avoided. This is the first time field trials have been used instead of model predictions. The trials show that carbon debt can be avoided and climate change mitigated by directly using unconverted CRP grasslands for cellulosic feedstock production. The results will be helpful in developing strategies for producing bioenergy crop systems.

The Impact

Total debt, which includes future debt created by additional changes in soil C stocks and the loss of substantial future soil C sequestration, can be constrained to 68 Mg CO2e·ha−1 if subsequent crops are under permanent no-till management. If tilled, however, total debt triples to 222 Mg CO2e·ha−1 on account of further soil C loss. Projected C debt repayment periods under no-till management range from 29 to 40 y for corn–soybean and continuous corn, respectively. Under conventional tillage repayment periods are three times longer, from 89 to 123 y, respectively. Alternatively, the direct use of existing CRP grasslands for cellulosic feedstock production would avoid C debt entirely and provide modest climate change mitigation immediately. Incentives for permanent no till and especially permission to harvest CRP biomass for cellulosic biofuel would help to blunt the climate impact of future CRP conversion.


Researchers report a full GHG accounting during the year of conversion of a 22-y-old CRP perennial grassland dominated by smooth brome grass (Bromus inermis) to a no-till soybean (Glycine max) system. No-till soybean is a recommended breakout crop for CRP conversion because of weed control and soil carbon conservation advantages.

Principal Investigator

Ilya Gelfand
Michigan State University

BER Program Manager

Dawn Adin

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Gelfand, I., T. Zenone, P. Jasrotia, J. Chen, S. K. Hamilton, and G. P. Robertson. 2011. “Carbon Debt of Conservation Reserve Program (CRP) Grasslands Converted to Bioenergy Production,” Proceedings of the National Academy of Sciences of the United States of America 108(33), 13864–9. DOI:10.1073/pnas.1017277108.