Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2008
Publication Date: 7/15/2008
Citation: Rhoton, F.E., Duiker, S.W. 2008. Erodibility of a Soil Drainage Sequence in the Loess Uplands of Mississippi. Catena. 75: 164-171. Interpretive Summary: Runoff and erosion losses from soils formed in the loess deposits of the lower Mississippi are generally considered to be the greatest in the United States due to generally low concentrations of cementing agents that bind soil aggregates into water stable units. The distributions of these cementing agents vary along slope positions due to differences in soil wetness. Since soil erodibility and erosion losses vary accordingly, there is a need to assess soil susceptibility under different slope/wetness conditions for delineating zones of potential erosion losses at watershed scales. We used total clay and water dispersible clay contents to calculate an aggregation index which is an indicator of soil erodibility. Using this approach, we showed that as the soils became wetter in the lower slope positions, an increase occurred in their susceptibility to erosion losses due to the loss of iron, aluminum, and silica oxide cementing agents. These results demonstrate the importance of determining the erodibility as a function of slope position when predicting runoff and erosion losses at watershed scales.
Technical Abstract: The susceptibility of loess soils in the lower Mississippi to runoff and erosion losses varies as a function of landscape position and mapping units. This study was conducted to determine the effects of soil drainage on physical and chemical properties that influence erodibility through their control of aggregate stability. Soil samples were collected from the A- and B-horizons of the five representative pedons in the Memphis catena whose drainage class varied from well-drained to poorly-drained. The fine earth fraction (<2 mm) of each soil was characterized for a range of basic soil physical and chemical properties. Additional sub-samples (<8 mm) were placed in a rainfall simulator pan (0.6 m x 0.6 m test area) and subjected to simulated rainfall at an intensity of 64 mm h-1. Soil erodibility was assessed by the use of an aggregation index (AI) computed from water dispersible clay (WDC) relative to total clay contents. The data show that as soil drainage classes became wetter, the percentage of sediment < 53 µm increased with a decrease in soil AI resulting from a loss of Fe, Al, and Si oxide cementing agents. These results suggest that cementing agents responsible for soil aggregate stabilization are mobilized under conditions of relatively low redox potentials which increase soil erodibility.