Surface Soil Aggregate Stability Under Forest and Grass Vegetation Across Landscape Positions.

Differences in surface soil aggregate properties are linked to differences in soil carbon sequestration associated with different land managements and landscape positions. This work considers surface soil aggregate properties as comparators of management and the environmental factors of bulk density, total carbon content and slope position. Aggregate stability and size distributions of surface soil were determined across major slope positions (summit, shoulder, backslope, footslope and toeslope) on three paired (forest and grasslands) zero-order basins in the Shawnee Hills region of Illinois, Indiana, and Kentucky. These site locations represent a loess-thinning sequence, with the sites in Illinois having loess 3-5 m deep at the summit while summits in Indiana have ~ 1 m loess.  Minimally disturbed surface soil samples (1 - 7 cm in depth) were collected from each of a minimum of 10 randomly generated points for the major landscape positions within the zero-order basins. Mean weight diameters were determined from 6 sieve fractions (1000 - 2000 µm, 500-1000 µm, 250 - 500 µm, 105-250 µm, 53 - 105 µm, and < 53 µm) of air-dried samples collected in close proximity (< 2 cm) to core samples collected for bulk density and total carbon determinations. Stability of macro-aggregates (diameter > 250 µm) was assessed by wet sieve method. Mean dry aggregate size is influenced by depth of loess deposit.  Wet sieve results will be discussed.