Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2012
Publication Date: 5/7/2012
Publication URL: http://handle.nal.usda.gov/10113/55926
Citation: Vogel, K.P., Follett, R.F., Varvel, G.E., Mitchell, R., Kimble, J. 2012. Soil carbon sequestration by switchgrass and no-till maize grown for bioenergy. BioEnergy Research. DOI 10.1007/s12155-012-9198-y. Interpretive Summary: Environmental benefits of bioenergy crops including corn and perennial grasses such as switchgrass are dependent on several factors including their effects on soil organic carbon. In 1998, a long term soil carbon study was established in eastern Nebraska for switchgrass and corn grown using no tillage (no-till) production methods. For each crop there were three different nitrogen fertilizer rates and two different harvest treatments. Soils were sampled at the beginning of the study and nine years later to a depth of 5 feet. In most previous soil carbon research, soils were sampled to a 1 foot depth. Average annual increase in soil organic carbon by both switchgrass and no-till maize was 1800 lbs per acre and over half the increase in soil carbon was below the one foot depth. Management practices affected the amount of the increase in soil carbon, but all changes were positive. These results indicate that the environmental benefits of growing non-till corn and switchgrass for bioenergy have been significantly underestimated in modeling and analyses studies to date because of failure to account for the significant large increases that occur in soil carbon deep in the soil profile for these crops.
Technical Abstract: Net environmental benefits of bioenergy crops including maize and perennial grasses such as switchgrass, are a function of several factors including the soil organic carbon (SOC) sequestered by these crops. In 1998, a long-term SOC study was established in eastern Nebraska for switchgrass and maize grown using no tillage (no-till) production methods. For each crop there were three different N fertilizer rates and two different harvest treatments. Soils were sampled to a depth of 1.5 m at the beginning of the study, nine years later, and periodically in between. After the first nine years, there were significant, positive increases in SOC for all soil depths and N rate x harvest treatment combinations except for the 0 N rate switchgrass for the 0 to 30 cm sampling depth. Both switchgrass and maize with best management practices had average annual increases in SOC that exceed 2 Mg C ha-1 yr-1 (7.3 Mg CO2 ha-1 yr-1). A hectare (ha) is 10,000 m2. For both switchgrass and maize, over 50% of the increase in SOC occurred below the 30 cm depth which is the soil depth on which most previous soil C sequestration data and modeling is based. These rates greatly exceed those used in previous modeling work on the net benefits of bioenergy crops. Results from this study, which is the longest term study established specifically to monitor SOC of switchgrass and no-till maize, indicate that the beneficial SOC sequestration of these crops deep in the soil profile has been disregarded or severely discounted by 60 to over 100% in modeling and analyses studies to date.