Soil Carbon Sequestration and Age in the Historic Grasslands

of the United States

 

Ronald F. Follett, USDA/AARS Soil-Plant-Nutrient Research Unit, Fort Collins, CO 80522 rfollett@lamar.colostate.edu

 

Eldor Paul, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523 eldor@nrel.colostate.edu

 

Steven W. Leavitt, LTRR, The University of Arizona

This project was initiated to increase our knowledge of global change related to the role of soil organic carbon (SOC) in sequestering atmospheric carbon dioxide (CO2), a greenhouse gas. The research focuses on the use of radiocarbon dating through accelerator mass-spectrometric measurement of SOC 14C activity to determine how long the carbon (C) has been sequestered in the soil. Radiocarbon dates of the SOC with profile depth from soil samples collected from grassland sites in CO, TX, MT NE, IA, MO, MN, OK, and ND were determined. These results show the very important role of soil for long-term sequestration of C as it may related to its exchange with atmospheric CO2. Grassland sites were sampled by horizon to a depth of about 2 m. Nearly one-half of the total weight of SOC is in the top 20 cm and up to one-third can be in the top 10 cm of the soil. The remaining one-half is located from 20 to 200 cm below the surface. The mass of SOC was between 85-150 t ha-1 in the top 2 m of soil. These data show the importance of protecting near-surface soil and its associated SOC from loss. 14C dating of soil C indicates that the one-half of the SOC that is sequestered below 20 cm has mean residence times (MRT) that are greater than 1000 to 2000 years. Soil C at depths of about 2 m has MRT of 9000 to 13000 years, but accounts for only about five percent of the total. Thus, once sequestered, immense amounts of SOC have remained in soil profiles for a very long time.

 

Publications:

 

Follett, R.F., Kimble, J., Leavitt, S.W. and Preussner, E., 2004. Potential use of soil C isotope analyses to evaluate paleoclimate. Soil Science 169: 471-488.

Follett, Ronald F., Leavitt, Steven W., Kimble, John M., and Pruessner, Elizabeth G., 2003. Paleoenvironmental inferences from d13C of soil organic carbon in 14C-dated profiles in the U.S. Great Plains. XVI INQUA Congress, Reno, NV, 23-30 July.

Follett, R.F., Paul, E.A., Leavitt, S.W., Halvorson, A.D. and Peterson, G.A., 1997. Determination of soil organic matter pool sizes and dynamics: 13C/12C ratios of Great Plains soils in wheat-fallow cropping systems. Soil Science Society of America Journal 61: 1068-1077.

Leavitt, S.W., Follett, R.F., Kimble, J.M., and Pruessner, E.G., 2007. Radiocarbon and d13C depth profiles of soil organic carbon in the U.S. Great Plains: A possible spatial record of paleoenvironment and paleovegetation. Quaternary International 162163: 2134.

Leavitt, S.W., Paul, E.A., Pendall, E., Pinter, P.J. and Kimball, B.A., 1996. Field variability of carbon isotopes in soil organic carbon. Nuclear Instruments and Methods in Physics Research B 123: 451-454.

Paul, E.A., Follett, R.F., Leavitt, S.W., Halvorson, A., Peterson, G. and Lyon, D., 1997. Determination of the pool sizes and dynamics of soil organic matter: Use of carbon dating for Great Plains soils. Soil Science Society of America Journal 61:1058-1067.

 

Figures: Soil Pit at Akron, CO (upper left); Native and plowed grasslands at Sydney, NB (upper right); Grassland maps (lower)

Akron SoilSydneyNB
Grasslands MapGreat Plains Site MapClick map to see larger version