MINERALOGY OF ERODED SEDIMENTS DERIVED FROM HIGHLY WEATHERED ULTISOLS OF CENTRAL ALABAMA

Authors: SHAW, J - AUBURN UNIVERSITY; Truman, Clinton; Reeves, Donald

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2002
Publication Date: 11/30/2002
Citation: Shaw, J.N., Truman, C.C., Reeves, D.W. 2001. Mineralogy of eroded sediments derived from highly weathered ultisols of central Alabama. Soil & Tillage Research. 68:59-69.

Interpretive Summary: Crop production systems on sandy soils in the southeastern USA have historically been managed with conventional tillage practices. Although clay contents are low in the surface of these soils, they play a major role in pollutant transport. Clay particles dispersed in run-off water from these soils is associated with soil erosion losses but can be reduced by conservation tillage management. We used a rainfall simulator to determine the impact of long-term tillage and crop residue management systems on clay contents of run-off water from a typical soil in the Southeastern Coastal Plain. Clay dispersed in run-off from the simulated rain was reduced with increases in soil organic matter content, as a result of management using conservation tillage and cover crops. These findings can be used by scientists and environmental managers in agencies like USDA-EPA and USDA-NRCS to facilitate development of computer models that predict sediment-attached losses of nutrients and pesticides from these soils to surface waters.

Technical Abstract: Coarse textured soils in the southeastern USA have historically been managed under conventional tillage practices. Although clay (<2 µm) contents are low in these surface horizons (typically <100 g/kg), this fraction plays a dominant role in colloidal facilitated pollutant transport. We evaluated sediment size and mineralogical partitioning of clay minerals of in situ soil vs. runoff sediment under simulated rainfall. In addition, because water dispersible clay (WDC) has been shown to be correlated with soil erodibility and can be affected by management practices, we evaluated WDC differences as a function of tillage. Plots were established in central AL on soils classified as coarse-loamy, siliceous, subactive, thermic Plinthic Paleudults and Typic Hapludults. Tillage treatments were established in 1988, and included conventional vs. no surface tillagetreatments, with residue remaining or being removed, and with or without paratilling (non-inversion subsoiling). Simulated rainfall (target intensity = 50 cm/h for 2 h) was applied to replicated 1m2 areas, and runoff and sediment were collected. Mineralogical analyses and quantification of soils and sediment were conducted using thermogravimetric (TGA) and x-ray diffraction (XRD) techniques. WDC was highly correlated with soil organic carbon (SOC%) (r2=0.76), which was increased with no-tillage and residue. Although no differences in the mineralogy of the <2 µm sediment were observed between tillage treatments, runoff sediments (<2 µm) were enriched in quartz and depleted with respect to kaolinite as compared to in situ soils. These findings will facilitate development of mechanistic models that predict sediment-attached losses of nutrients and pesticides.