Owensby, Clenton (Kansas State Univ., Department of Agronomy, Manhattan, KS, 66506-5501; Phone: 785-532-7232; Email: owensby@ksu.edu)

Carbon and Water Vapor Fluxes in Grazed and Ungrazed Tallgrass Prairie

C. E. Owensby *, J. M. Ham, L. M. Auen

In order to determine the potential of grasslands to sequester carbon, carbon dioxide fluxes have been measured on tallgrass prairie grazed at ungrazed, moderate, and heavy rates using eddy correlation aerodynamic systems. Flux data are measured continuously and recorded as 30-minute average fluxes. The initial grazing treatments were designed to show the impact of grazing at twice the recommended rate for a 3-yr period, followed by reverting to recommended grazing rates and measuring fluxes for a 3-yr period. During the initial year (2003) grazing heavily resulted in a net carbon balance of –92 g

m^-2 compared to +33 g m^-2for a moderately grazed area for a difference of -125 g m^-2. It appears that the mid-season dry conditions accentuated the carbon losses from the system on the heavily-grazed area compared to the moderately-grazed in 2003. Incomplete carbon flux data from 2004 show similar relationships to those in 2003 between moderately-grazed and heavily grazed areas.