Aquerts and aquertic soils: A querulous proposition

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Aquic Conditions and Hydric Soils: The Problem Soils


Vertisols and aquic moisture regimes have had a contentious relationship. Only very recently were aquic moisture regimes considered appropriate for Vertisols, and even now many soil scientists do not consider the wetter Vertisols to be hydric soils. Part of the problem is that understanding water table dynamics in Vertisols is problematical: shrink-swell action results in a dynamic pore-size distribution that is a function of moisture content. In addition, the very clayey matrix of Vertisols results in a hydrologic disequilibrium between the voids and the matrix. We explore a series of problems for defining hydric status that arise due to the unique nature of Vertisols. Results of field studies on the Texas Gulf Coast Vertisol belt demonstrate the significance of hydrologic and biogeochemical disequilibrium for defining hydric Vertisols. Vertisols on planar surfaces were saturated, as measured with both tensiometers and piezometers, >50% of the time, yet experienced much shorter periods of reduction, and were never reduced in the entire matrix. Definitions for hydric soils should be reformulated to include specific periods and volumes of reduction. We present some tentative field criteria for identifying hydric Vertisols.

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