Field Index for Quantifying Vesicular Horizon Morphology: Development and Application

Vesicular horizons influence hydrology, ecology, and erosion processes in arid environments. This study was carried out in order to develop an index for quantifying the strength of vesicular horizon development and to relate the index to soil physical and geomorphic properties. Descriptions of vesicular horizons and corresponding soil properties were gathered from Natural Resource Conservation Service databases and several sources in the scientific literature. The index is based on properties included in most pedon descriptions and is calculated as follows:

VHI = T(S_p*Q_p + S_pl*G_pl + S_col*G_col)

Where VHI = vesicular horizon index, T = horizon thickness (in cm), S_p = size class of vesicular pores (assigned 1-5 for vf-vco), Q_p = quantity class of vesicular pores, S_pl = size class of platy structure (assigned 1-5 for vco-vf), G_pl = grade of platy structure, S_col = size class of columnar of prismatic structure (assigned 1-5 for vco-vf), G_col=grade of columnar or prismatic structure. More terms for pores and structure (e.g.,S_p*Q_p for pores) are added if more than one size class is described. If more than one vesicular horizon is described the VHIs are added to determine the total VHI for the soil. The index was found to increase with age of the geomorphic surface (0.2 ka-130 ka) at several chronosequence sites and the index was higher for finer textured vesicular horizons. The index developed in this study is a simple way of quantifying vesicular horizon development, which has potential applications in relating soil morphology to hydrologic and ecological functions of desert soils and landscapes.