Soil Characteristics and Cracking Behavior of a Vertisol Catena.

When shrink-swell soils dry, vertically-oriented cracks facilitate rapid transport of surface water into subsoil. However, the applicability of models that account for crack formation and associated hydrology is hindered by poor understanding of the phenomena of crack formation and closure across a catena. The overall objective of the research is to study the influence of soil properties and terrain on surface hydrology in shrink-swell soils by quantifying the temporal and spatial variability of soil subsidence. Six sites on a catena were selected based on landscape information and soil electrical conductivity measurements. At each of the sites, soil properties were analyzed, along with bi-weekly measurements of soil subsidence and soil moisture. Metal rods were anchored at different depths to measure the vertical subsidence. The change in absolute heights of rods was used to track the temporal trends in thickness of soil layers. A neutron access tube was installed to measure soil moisture. The study suggested that soil subsidence was not spatially varied significantly in a Houston Black series over time. However, Heiden soils developed in area where the soil depth is shallow was significantly different. Soil shrinkage was consistently more active in the subsoil, 40-80 cm. The soil layer of 20-40 cm did not significantly contribute to soil movement on the summit and shoulder, but had a more significant contribution at the backslope and footslope. Coefficient of linear extensibility (COLE) was significantly related to inorganic carbon (IC),CEC but low correlation with fine clay. This implies that IC has a strong impact on the COLE of the soils. This shows that IC is an important soil property in accounting for the spatial and temporal variation of crack volume across this Vertisol catena.