Vertisol Morphology, Classification, and Seasonal Cracking Patterns in the Texas Gulf Coast Prairie

Vertisols have unique morphology and the capacity to change volume with changes in water content; therefore, they are well known for their spatial and temporal variability. Our objectives were to address the spatial variability of Vertisol surface and subsurface features, as well as the spatial and temporal variability of Vertisol cracking. First, we discuss surface and subsurface features of Vertisols based on the literature and more than three decades of interagency soil investigations in the Texas Gulf Coast Prairie. Second, we report on a 10-yr field study of location, length, width, depth, and duration of seasonal crack openings in a 100-m2 area of Laewest clay (fine, smectitic, hyperthermic, Typic Hapludert) with gilgai in a native grassland south of Victoria, TX. Results of the crack monitoring showed that cracks always started on, and crack density was greater on, microhighs or the upper part of microslopes. Under prolonged drying periods, cracks formed on microlows and were, on average, deeper in microlows. Cracks generally occurred in the same location within a year. Between years, crack locations shifted slightly, although they were clustered in the same general areas during the 10 yr of study. Vertisol cracking was affected not only by seasonal fluctuation of precipitation, but also by multiple-year precipitation cycles. Analysis of precipitation over several decades indicated that the Ustert/ Udert classification criteria based on cracking in normal precipitation years was never met in this region of Texas because there were never eight normal months within a normal year. Normal yearly precipitation standards and months on a regional basis would provide better precipitation norms for soil classification. abstract