Soil properties, and cotton growth, yield and fibre quality in three cotton-based cropping systems

Abstract

The effects of three cotton-based cropping systems on soil properties, black root rot severity, and growth of cotton in a Vertisol were evaluated after a series of floods in eastern Australia. The experimental treatments, which had been imposed since 1985, were conventionally and minimum-tilled continuous cotton, and minimum-tilled cotton–wheat rotation. Frequent rainfall and flooding during the winter of 1998 resulted in near saturated soil at spring sowing in October. Although conventional tillage operations were completed before flooding, minimum tillage operations were not possible due to excessive moisture and cotton was sown onto the old beds with no-tillage. Soil specific volume (electrical conductivity of a 1:5 soil:water suspension) EC 1:5, exchangeable Na content, pH and organic C were determined for the top 0.6 m of the profile in summer 1998 and again in 1999. Organic C in the surface 0.10 m was also evaluated during 1998–2000. Black root rot severity and mycorrhizal fungal colonisation were evaluated at 6 weeks after sowing. Tissue nutrient concentrations were measured in mature cotton plants. Cotton lint yield and fibre quality were evaluated after picking and ginning. In comparison with either minimum- or conventionally tilled continuous cotton, minimum-tilled cotton–wheat rotation had the lowest exchangeable Na content and severity of bacterial black root rot, best surface structure and the highest crop growth, nutrient uptake and lint yields. Subsoil structure was the best with conventionally tilled continuous cotton. The 1998 floods appear to have decreased exchangeable Na and increased soil pH in all treatments. Surface organic C also decreased between 1998 and 2000. Soil structural damage was minimised by avoiding tillage and trafficking in wet conditions. Compared with 1998, average yield decreases in 1999 were of the order of 43%. Cotton lint fibre quality was also poorer in 1999.