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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In 1982, a long-term project was established in central Queensland to study the effect of crop type, crop rotation, and tillage practice on runoff and soil loss. Runoff and soil loss were measured at the outlet of 9 large contour bay catchments (approximately 13 ha) where wheat, sorghum, and sunflower were grown in 3 crop sequences. Each crop sequence consisted of zero, reduced, and conventional tillage fallow practices. Monoculture cropping was practised from 1983 to 1985, then opportunity cropping from 1986 to 1993. During the study, wheat cropping had lower average annual runoff and soil loss (P < 0·01) than sorghum and sunflower. Zero and reduced tillage retained more crop stubble (median >50%) and had less soil loss (P < 0·05) than conventional tillage. Zero tillage wheat had the lowest average annual runoff and soil loss, and conventional sunflowers had the highest. The erosion risk associated with sunflowers was reduced by a wheat–sunflower crop rotation, particularly when zero-tilled. Monoculture sunflower must be avoided. The region is susceptible to large episodic erosion when crops are not sown, there are long fallows, and soil cover falls below levels critical to control erosion (<30%). Opportunity cropping is the most appropriate system to maximise the regions variable rainfall and reduce runoff and soil loss.