Characterization of a Pimple Mound‐Intermound Soil Complex in the Gulf Coast Prairie Region of Texas

Natural mound and intermound soil pedons were characterized to investigate native mound‐intermound formation and soil properties that may explain unfavorable plant growth that has been observed on sites of truncated mounds. Subrounded mounds average 26‐m apart, 15 m in diam., and 0.5 m in local relief. Mound soil has a thick silt loam A horizon, silt loam E, B/E, and BE horizons, and thick, weakly expressed Bt (argillic) horizons of silt loam to clay loam texture. Upper mound horizons are acid, and the lower Bt horizon is neutral to calcareous. Calcareous intermound soil, originally mapped as Morey (fine‐silty, mixed, thermic Typic Argiaquolls) silt loam, has a silt loam A horizon above clay loam cambic and calcic horizons. Better infiltration and drainage in the mound contrasts with very slow runoff and poor infiltration and drainage in the intermound. Mound and intermound mineralogy is similar, with mainly quartz in coarse silt and very fine sand separates, kaolinite and quartz in coarse clay, and smectite and kaolinite in the fine clay fractions. Carbonate, base saturation, pH, and illuviation argillan distributions suggest predominantly downward water flow with desiccation and rewetting cycles in the mound soil, contrasted with more prolonged periods of wetness in the intermound soil. Particle size and Ti and Zr distributions indicate a definite parent material break above the mound Bt horizon, but no clear break in the intermound. Properties of the loamy mound soil investigated are consistent with a mechanism of local wind or water deposition around clumps of vegetation. Soil surface exposed by mound truncation is a poor plant growth medium because it consists of acid, silty, slightly buffered material with low organic matter content and weak structure.