Effects of Landscape Position and Reconstructed Prairie Age in Cultivated Cropland On Soil Organic Carbon and Aggregate Formation Dynamics.

Changes in land use and alteration of the ecosystem can significantly affect soil organic carbon (SOC) and soil aggregation dynamics. It was documented that there was a 10 to 40% reduction in soil organic matter due to conversion of tall-grass prairies to cropland in the mid-1800s in Iowa. Little is known on interrelationships between soil aggregation and SOC dynamic after tillage has ceased. The objective of this study was to examine plant and soil interactions effect on soil aggregates formation and SOC dynamics. Study was conducted in south central Iowa from 2005 to 2008. There were three reconstructed prairie sites varying in establishment year; 1993, 1998, 2003, a row crop production no-till site, and a prairie remnant site. All soil, plant, and CO₂ measurements were located on summit, mid-slope, and toe-slope positions. Results from this study show that the remnant prairie site had greater SOC content in the summit and mid-slope positions than did the reconstructed prairies and cropland site, although SOC in the toe-slope position was not significantly different between sites. Increases in SOC sequestration of reconstructed prairies were the largest during the first decade since prairie establishment. Increases in SOC sequestration rates coincided with increases in soil macro-aggregate associated C in 2-0.25 mm size fractions. This suggests that the mechanisms of soil aggregate formation aids in stabilizing soil SOC, which is significantly affected by slope position and years since prairie establishment.