The effects of landforming on soil profile characteristics of an irrigated cotton-producing area of southeastern Australia

Broadacre, irrigated cotton production in Australia is reliant on landforming to optimise water-use efficiency during the growing season. A side-effect of landforming, or “cut” and “fill” operations, is that the suitability of land for crop production may be altered by the removal, addition, exposing or raising of surface or near-surface soil layers. For landowners considering bringing new areas of land into irrigated crop production, knowledge of what these alterations will be is crucial in determining the likely success of such a venture. In this study, the effects of landforming on the profile attributes of three soil types in a relatively new cotton-growing area of southeastern Australia are examined. For each soil type, profiles in landformed fields, including both “cut” and “fill” profiles, are compared to uncropped (“native”) profiles within and below the zone of soil disturbance typically involved in landforming. Although the topsoil features of landformed profiles differ to those of native profiles for each of the three soil types, the oldest and most pedologically differentiated soil type exhibits the greatest change from the native state following the cut and fill operations. In this case, landforming has served to scalp or mix a thin topsoil layer with significantly more clayey, alkaline and sodic subsoil material, which accounts for landowner observations of poor cotton yields on this soil type. Topsoil properties of the landformed profiles of the other two soil types are not as limiting to plant growth, and so the potential side-effects of landforming on crop production are less.