Iron oxides erodibility interactions for soils of the Memphis catena

In the Memphis catena, the well-drained Memphis (fine silty, mixed, active, thermic Typic Hapludalfs) is more erodible than the moderately well-draine d Loring (fine silty, mixed, active, thermic Oxyaquic Fragiudalfs) and Gren ada (fine silty, mixed, active, thermic Glossic Fragiudalfs). We hypothesiz ed that soil wetness and Fe oxide status affects the erodibility of these s oils. Samples (<2 mm) of A- and B-horizons, collected from representative p edons at five locations, were characterized for standard physical and chemi cal properties. Simulated rainfall was applied (64 mm h(-1)) to additional samples (<8 mm) in a rainfall simulator pan that had a 0.6 m x 0.6 m test a rea. Water dispersible clay (WDC) and soil loss averaged 7.2% and 9.21 Mg h a(-1) for Memphis, 6.8% and 8.85 Mg ha(-1) for Loring, and 6.1% and 8.71 Mg ha(-1) for Grenada. Sediment Fe-0, Fe-d, and Fe-0/Fe-d ratios were about 0 .80, 1.5, and 0.50 times that of the soil, respectively. Correlation coeffi cients (r) for WDC and soil loss vs. Fe oxide variables exceeded 0.90 in so me horizons, whereas, organic C (OC) and % clay were generally <0.60. Howev er, OC vs. % sediment <53 mu m had r values of 0.87 compared to 0.59 for so me Fe oxide variables. Regression models derived for WDC and soil loss had Fe oxide parameters as principal variables in the best fit models and coeff icients of determination that ranged from 0.208 to 0.922 (significant at P less than or equal to 0.01). Results suggest that Fe oxides are more import ant than OC and clay content for determining the erodibility of these soils , particularly Fe-0/Fe-d ratios which are negatively correlated with WDC an d soil loss.