Abstract

Tripp (coarse-silty, mixed, mesic Aridic Haplustolls), and Mitchell (coarse-silty, mixed (calcareous), mesic Ustic Torriorthents) soils of western Nebraska have frequently exhibited high ratios of 1500 kPa water content to percent measured clay. Both soils were known to contain considerable amounts of volcanic glass. The objective of the study was to determine if the anomalous ratios were related to the presence of volcanic glass or associated minerals. Allophane was not present as determined by differential scanning calorimetry, thermal gravimetric analysis, elemental analysis of acidoxalate extractions, or pH dependent CEC. The separate particle size fractions were analyzed using X-ray diffraction (oriented mounts), SEM, optical mineralogy and tested for CEC and specific surface. These tests and observations suggested the high ratios were related to the presence of nondispersing smectite coatings on particle surfaces within the sand and silt fractions of the Tripp and Mitchell soils.