Submitted to: CSA News
Publication Type: Popular Publication
Publication Acceptance Date: July 12, 2006
Publication Date: August 1, 2006
Citation: Allen Jr, L.H. 2006. Does CO2 enrichment of perennial forages enhance soil carbon accumulation? CSA News. 51(8):10 Interpretive Summary: Atmospheric carbon dioxide (CO2) is increasing due to burning of fossil fuels, which could enhance the greenhouse effect and cause global warming. Carbon sequestration in soils could lessen CO2 increases. Soils of natural grasslands accumulate carbon. However, little research has been done on managed, subtropical grassland species, and less on impacts of elevated CO2 and temperature on soil carbon. In a six-year study, ARS and University of Florida scientists determined the effect of both CO2 and temperature on accumulation of soil organic carbon by bahiagrass and perennial peanut grown on previously cultivated soil. Bahiagrass accumulated more soil carbon than perennial peanut, 2.8 and 1.5 pounds per ton of soil, respectively. Perennial peanut gained more soil carbon in 700 than 360 ppm CO2 (1.9 and 1.1 pounds per ton, respectively). However, soil carbon gains of bahiagrass at these CO2 levels were similar (2.9 and 2.7 pounds per ton). An 8 degree F temperature increase caused soil carbon gains to decrease from 2.4 to 1.8 pounds per ton. These subtropical grassland species gain soil organic carbon like other natural grasslands. Thus, managed grassland species in the humid southeastern USA can help sequester soil carbon.
Technical Abstract: Carbon sequestration in soils could mitigate atmospheric carbon dioxide (CO2) increases. Studies were conducted on elevated CO2 and temperatures effects on accumulation of soil organic carbon (SOC) and nitrogen (SON) by forages growing on previously cultivated land. Two subtropical species, bahiagrass (BG) and rhizoma perennial peanut (PP), were grown in field plots at baseline-ambient, +1.5, +3.0, and +4.5C in four temperature-gradient greenhouses, two each at 360 and 700 ppm CO2. The top 20 cm of soil was sampled in February 1995 and December 2000 before and after the project. The BG accumulated more SOC than PP across the six years, 1.40 and 0.75 g/kg, respectively. Mean SOC gains of BG at 700 and 360 ppm CO2 were not different (1.45 and 1.34 g/kg, respectively), but mean SOC gains of PP were greater in 700 than 360 ppm (0.95 and 0.54 g/kg, respectively). Temperatures of +3.0 and +4.5C caused SOC gains to decrease. Relative SON increases were similar to SOC. Conversion to forage from cultivation caused SOC to accumulate especially by BG. Elevated CO2 promoted accumulation of SOC in PP but not in BG. Elevated temperature decreased accumulations of SOC. Subtropical forage species gain SOC similarly to reports of other species.