Proposed Taxonomic Classification of Gypsum-Rich Soils from West Texas and Southern New Mexico

Many standards for describing and classifying soils are inadequate for extensive areas in West Texas and Southern New Mexico that are rich in gypsum. The following framework is submitted for consideration by the soil science community.

The definition of B horizons is broadened to include horizons with transformed or translocated gypsum. We assert that if gypsum in the soil zone gets wet, it has a pedogenic origin. The proposed horizon subscript “yy” will be used to identify gypsum-dominated horizons. A hypergypsic diagnostic horizon and the great group Hypergypsids are proposed to accommodate soils with high gypsum content at a higher category in Soil Taxonomy. Otherwise, Haplogypsids encompass soils with gypsum content ranging from 5 to 95 percent. Revised definitions of gypsic and petrogypsic horizons do not require illuvial gypsum. This avoids the necessity of distinguishing inherited, translocated, or transformed gypsum. Three substitute-for-particle-size classes are proposed.

Under this proposal, all soils that contain gypsic, hypergypsic, and petrogypsic horizons, and that have an aridic soil moisture regime would be considered Gypsids. No soil with greater than 5 percent gypsum content would remain as a Torriorthent. Subgroup classes that group soils with differing limitations and potentials for use and management are proposed. The presentation will compare the classification of gypsum-rich soils under the existing and proposed taxonomic structures.

Three needs exist to support this proposal. First, field and laboratory protocols will be required to identify the appropriate substitute-for-particle-size class for a particular specimen. Second, statistical analysis of relationships between gypsum content and saturation water content, 0.01 MPa water content, 1.5 MPa water content, and Cation Exchange Capacity is necessary to identify the critical gypsum content to differentiate gypsic and hypergypsic diagnostic horizons. Third, confirmation of gypsum content for pedons analyzed by NSSL prior to 2006 is needed.