Gehl, Ron (Kansas State Univ., Dep. of Agronomy, Manhattan, KS, 66506-5501; Phone: 785-532-7212; Fax: 785-532-6094; Email: rgehl@ksu.edu)

Landscape Position and Watershed Treatment Impacts on Spatial Distribution of Soil Organic Carbon

R.J. Gehl *, C.W. Rice, M.D. Ransom, R.S. Blaisdell, J.W. Stuth

Evaluating the influences of topography and watershed management of native grasslands on soil C content is an important component to improving our overall understanding of terrestrial soil C dynamics. A joint effort of Kansas State University and Texas A&M University began in 2002 to determine the effects of landscape position and watershed treatment on soil organic carbon (SOC) content at the Konza Prairie Biological Station (Manhattan, KS). Soil samples were collected at depths of 0-5, 5-15, and 15-30 cm in each of 6 watersheds. Each watershed had a distinctive treatment including a combination of grazing or no grazing and one of 3 prescribed burn sequences: annual, 4-yr interval, or 20-yr interval. Soil samples were collected at the interfluve, sideslope, footslope, and toeslope landscape positions. Samples were analyzed for %C using near infrared reflectance spectroscopy (NIRS). Initial comparisons of 4 watersheds (non-grazed, 20-yr; grazed, 20-yr; non-grazed, 4-yr; and non-grazed, 1-yr) across all slope positions indicated that only the non-grazed annually burned watershed had significantly lower (P = 0.05) C content (2.68 %C) at the surface 0-5 cm, and no differences were detected at the 5-15 or 15-30 cm depths. No significant differences in slope position were detected in the surface 0-5 cm, while the toeslope position of three non-grazed watersheds had less C in the 5-15 cm depth and the non-grazed, 20-yr burn watershed had less C at the toeslope in the 15-30 cm depth. Comparisons of slope position across the four watersheds indicated differences in SOC only in the 5-15 and 15-30 cm depths. Future research will include additional sampling at the watersheds and analysis of samples using dry combustion.