The effects of landforming on crop production on a red-brown earth

Abstract

Crop growth on the exposed subsoils of Macquarie Valley red-brown earths, which have been levelled for flood irrigation development, is much less than on undisturbed and fill areas. A project was carried out to quantify the differences in properties between topsoil and exposed subsoil and to relate these differences to observed crop performance. Cotton growth was measured on cut (surface soil removed) and fill (additional surface soil added from cut areas) sites. Soil samples were collected from both sites for chemical and physical analysis. To supplement these measurements pot experiments were conducted using cut and fill soils, a mixture of the two to simulate mixing in the field, all with or without gypsum. In the field, cotton growth on the cut soil was less than half that on the fill due to lower emergence and slower subsequent growth. Pot experiments confirmed these differences, although the surface structural problems were exacerbated by the rapid wetting of soil in pots. Differences between the surface of the cut and fill soils were attributed to the poorer development and lower stability of structure in the exposed subsoil. Below 30 cm, ESP, EMgP and Dispersion Index were higher in the cut than in the fill sites; ECaP and pH were lower. The pot experiments indicated that mixing of topsoil and subsoil improved emergence and subsequent growth, compared with the exposed subsoil, but gypsum had no significant ameliorative effect.