The effect of wet cultivation on the structure and fabric of a Vertisol

SUMMARY Changes in soil structure and fabric of a Vertisol in northern New South Wales, Australia following pre‐sowing cultivation at two different soil water profiles (dry and wet) were investigated. Both the dry and wet cultivated plots had similar, intensive pre‐sowing cultivation typical of commercial practice for irrigated cotton. For thin section analysis two profiles were sampled prior to this cultivation, and three from each of the dry and wet plots were sampled after cultivation. Samples were also available from soils in the area which had never been cultivated. All soils had porphyric fabric with vo‐ma‐skel‐insepic plasmic fabrics and a wide range of pedological features. The cultivated soils had other pedological features not present in the ‘never’‐cultivated soils, i.e. zones within which the plasma exhibited a moderately‐ to strongly‐striated orientation pattern. The more strongly‐striated units included occasional, very fine to fine joint planes. These zones were domi‐nantly equant to planar with sharp boundaries. Internally, they consisted of layer silicate plasma and mineral skeleton grains most commonly similar to the enclosing material. The proportion of these features differed between treatments especially in the 0.05‐0.25 m layer. Soil cultivated dry, and land prior to cultivation had < 1 % of their area composed of zones of striated clay, compared to up to 17% in the wet cultivated soil. This may be related to a greater incidence of shearing of soil in a plastic state by tillage implements and tractor wheels. In the dry cultivated soil shear appears to be of minimal significance.