Close-Interval Spatial Variability of Udertic Paleustalfs in East Central Texas

Abstract

Close-interval spatial variability analysis of the Tabor soil mapping unit in Brazos County, Texas, depict a stream terrace soil with well-developed gilgai-like subsurface microhighs and microlows. Computer-generated topographic surface nets of the contact between the surface (A+E) and subsurface (Bt) show enclosed basins and ridges. Approximately 31% of the 10-m2 area studied was classified as subsurface microknolls, whereas 25% was subsurface microdepressions and the remaining 44% represented transitional zones between the subsurface highs and lows. Soil characterization of three paired pedons (six profiles), with differing epipedon thicknesses, from within the sampled grid system indicates that, despite strong morphological evidence of vertic features, only two of the three subsurface microhighs and none of the microlow profiles met coefficient of linear extensibility (COLE) and potential linear extensibility (PLE) vertic classification criteria. Extrapolation of these data to the surrounding grid, based on subsurface Bt expression, suggests that approximately half of the total area can be considered vertic by present definitions. Soils with such intermittent and discontinuous vertic conditions would more appropriately be classified as Ruptic Vertic Paleustalfs. Alternatively, it is proposed that the vertic criteria be revised to include vertic features such as slickensides, either independently or in conjunction with COLE and PLE indices, to reveal the presence of potential hazards resulting from soil-strength failure.