Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 1998
Publication Date: N/A
Interpretive Summary: Soil erodibility can change over relatively short distances within the same field depending on where the soil occurs along a given slope. This implies that soil drainage conditions are responsible for the differences in erodibility, however, the exact processes have not been fully understood. We determined that changes in erodibility for different soils occurring on the same slope were related to changes in the type of iron oxides present. The distribution of these components is determined by soil drainage. Land-users should be aware of these potential differences in soil erosion within fields when developing management plans. Additionally, this information is vital to researchers concerned with modeling soil loss and predicting sediment yields from watersheds.
Past erodibility studies conducted on the soils of the Memphis catena have shown that the well-drained Memphis was more susceptible to erosion than the moderately well-drained Loring and Grenada. This study was conducted to determine how soil wetness and Fe oxide status affects the erodibility of these soils. Representative toposequence members were sampled at five locations between northwestern Tennessee and southeastern Louisiana. Samples from A- and B-horizons were air-dried, sieved to <2 mm, and characterized for magnetic susceptibility, water dispersible clay (WDC), citrate-bicarbonate-dithionite (Fed) and acid ammonium oxalate (Feo) extractable Fe, in addition to a range of standard physical and chemical properties. Additional samples sieved to <8 mm were placed in a rainfall simulator pan with a 0.6m x 0.6m test area. Rainfall was applied to both dry and wet soil conditions at an intensity of 64 mm/h for a duration of 1 h. Water dispersible clay contents and soil loss averaged 7.2% and 9.21 Mg/ha for Memphis, 6.8% and 8.85 Mg/ha for Loring, and 6.1% and 8.71 Mg/ha for Grenada over the five sites. The correlation coefficients for WDC vs soil loss, Fed, and Feo were highly significant (P <0.01). Both WDC and soil loss were negatively correlated with Feo/Fed ratios. Apparently, soil loss rates were determined by WDC which decreased between upslope (Memphis) and downslope (Grenada) positions as did Fed contents. The positive correlation between soil loss and Fed suggest that portions of this Fe oxide fraction occur as discrete particles that do not contribute to aggregate stability. Conversely, the negative correlations between WDC and Feo/Fed ratios suggest that the Feo fraction is more important to aggregate stabilization and promotes lower soil susceptibility to erosion.