Soil Carbon Storage by Switchgrass Grown for Bioenergy

Authors: Liebig, Mark; Schmer, Marty; Vogel, Kenneth; Mitchell, Robert - Rob

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2008
Publication Date: 12/10/2008
Citation: Liebig, M.A., Schmer, M.R., Vogel, K.P., Mitchell, R. 2008. Soil Carbon Storage by Switchgrass Grown for Bioenergy. BioEnergy Research. 1:215-222.

Interpretive Summary: Use of perennial herbaceous crops has been suggested to reduce negative environmental and social consequences associated with biofuel production due to their lower requirements of agricultural inputs relative to annual crops and their ability to be grown on marginal land. Among the portfolio of herbaceous perennial bioenergy crops considered for adoption throughout the USA, switchgrass (Panicum virgatum L.) has shown promise as a cellulosic ethanol source due to its high productivity across a large geographical domain. Purported environmental benefits associated with switchgrass production requires information on net greenhouse gas emissions, of which data on carbon dioxide update and subsequent sequestration in soil is a key component. To date, nearly all information on soil carbon change under switchgrass have been based on either modeled assumptions or small plot research. Accordingly, information on switchgrass-induced changes in soil organic carbon across field-scale, on-farm environments is lacking. To address this need, we measured change in soil organic carbon under switchgrass at 10 sites along a transect from North Dakota to Nebraska, USA. The sites, located on farmer fields managed for bioenergy production, were sampled prior to planting switchgrass and five years later to determine change in soil organic carbon over time. Switchgrass was found to affect change in soil organic carbon at all sites. Across sites, soil organic carbon increased significantly at 0-30 cm and 0-120 cm, with accrual rates of 1.1 and 2.9 Mg C/ha/yr (4.0 and 10.6 Mg CO2/ha/yr), respectively, demonstrating the potential of switchgrass as a carbon-negative bioenergy crop within the central and northern Great Plains. Monitoring sites are needed in major agro-ecoregions to assess long-term environmental effects of switchgrass production.

Technical Abstract: Life-cycle assessments (LCAs) of bioenergy crops such as switchgrass (Panicum virgatum L.) require data on soil organic carbon (SOC) change and harvested C yields to accurately estimate net greenhouse gas emissions. To date, nearly all information on SOC change under switchgrass has been based on either modeled assumptions or small plot research, both of which do not take into account spatial variability within or across sites for an agro-ecoregion. To address this need, we measured change in SOC and harvested C yield for switchgrass fields on ten farms in the central and northern Great Plains, USA. Change in SOC was determined by collecting multiple soil samples in transects across the fields prior to planting switchgrass and again five years later after switchgrass had been grown and managed as a bioenergy crop. All fields were sampled to a depth of 30 cm, while three fields were sampled to 120 cm. Across sites, SOC increased significantly at 0-30 cm (P = 0.03) and 0-120 cm (P = 0.07), with accrual rates of 1.1 and 2.9 Mg C/ha/yr, respectively, demonstrating the potential of switchgrass as a carbon-negative bioenergy crop within this agro-ecoregion. Change in SOC across sites varied considerably, however, ranging from -0.6 to 4.3 Mg C/ha/yr for the 0-30 cm depth; such variation in SOC change must be taken into consideration in LCAs. Increased reliance on agriculture for energy production underscores the need for long-term environmental monitoring sites in major agro-ecoregions. [GRACEnet Publication]