Soil Shrinkage Relationships of Texas Vertisols: I. Small Cores

Yule, D. F.; Ritchie, J. T.

Soil Shrinkage Relationships of Texas Vertisols: I. Small Cores

1980

Yule, D. F. | Ritchie, J. T.

Soil shrinkage-water content relationships are needed to describe pore size distribution, bulk density function, and potential vertical movement of Vertisols. Ten-centimeter long, 10-cm diam cores were collected from the 10- to 20-, 40- to 50-, 70- to 80-, 100- to 110-, and 130- to 140-cm depths of eight central Texas Vertisols. Four sites were adjacent mound and depression samples from two gilgai complexes. Profile description and analytical characterization were obtained for each site. Soil shrinkage was measured vertically and horizontally during a drying cycle from field water content to oven-dry. Some field matric potential profiles were obtained at sampling. The shrinkage curves are described in terms of structural, shrinkage, and residual water loss phases. All cores had normal, equidimensional shrinkage. Only sites sampled at matric potentials > −300 cm of water had structural water loss. The intersection between the structural and shrinkage phases (the swelling limit) was generally sharply defined when present and occurred at about −0.3 bar. Structural water loss increased with depth due to increasing matric potential, and the soil air content at the swelling limit was about 0.05 cm³/cm³. The water content at the swelling limit was related to the cation exchange capacity (CEC) and the −0.3 bar water content. The shrinkage limit was relatively constant (0.09–0.11 g/g) for seven of the sites, and all residual water loss occurred at < −15 bars. The total vertical shrinkage and the normal water loss were related to the CEC and to the coefficient of linear extensibility (COLE).

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