Tuesday, November 6, 2007
218-3

Soil Change during Three Decades of No-till, Conventional till, and Afforestation at the Horseshoe Bend Research Site in the Georgia Piedmont.

Scott Devine1, Daniel Markewitz1, Paul Hendrix2, and David Radcliffe3. (1) Warnell School of Forestry and Natural Resources, The University of Georgia, DW Brooks Drive, Athens, GA 30602, (2) 1033 Green Street, University of Georgia, University of Georgia-Athens, Institute of Ecology, Athens, GA 30602, (3) Crop & Soil Sciences, University of Georgia, University of Georgia, 3111 Miller Plant Sciences, Athens, GA 30602

Different land uses have variable effects on soil properties and functions which has implications for biogeochemical cycles. We investigate the treatment effects of conventional tillage (CT), no-tillage (NT), and succession to forest (NS) on soil nutrient cycling and storage at the Horseshoe Bend (HSB) tillage experiment established in 1978. We characterized soil chemical properties to 2 m to assess soil change and quantified soil aggregate stability in the upper 15 cm. An aggregate stability index based on the ratio of the mean weight diameter (MWD) of dry aggregates to the MWD of wet-sieved aggregates shows increasing stability from CT to NT to NS in both 0-5 and 5-15 cm depths but no difference between CT and NT from 5-15 cm. NS soils showed significantly lower soil pH to 2 m with greatest differences from 0-50 cm. NT and CT have greater effective cation exchange capacity (ECEC) to 2 m, possibly a result of pH dependent charge. Higher Ca, K, and Mg levels in CT and NT occur below the plow layer after nearly three decades of agricultural management. Significantly elevated levels of Ca penetrate to 200 cm, K to 100 cm, and Mg to 50 cm. Exchangeable acidity in NS decreases from a peak of 1.00 ± 0.23 cmolc/kg (57% base saturation (BS)) from 5-15 cm to a mean of 0.02 ± 0.006 cmolc/kg from 50-200 cm (BS >98%). This suggests that in the absence of liming, a combination of base cation uptake by the forest vegetation and solution leaching has led to re-acidification from the surface to 50 cm depth. Below 50 cm, residual liming effects from previous pasture management are apparently still evident.