Cropping systems and bed width effects on runoff, erosion and soil properties in a rainfed Vertisol

The effects of two bed widths (1 and 2m) and four rainfed cotton-based cropping systems on soil properties, runoff and erosion were evaluated in a Vertisol (1 per cent slope; 21g per 100g sand, 12g per 100g silt, 67g per 100g clay) in subtropical central Queensland, Australia. The cropping systems were: early cotton (Gossypium hirsutum L.) sown between August and October; wheat (Triticum aestivum L.) sown in May, sprayed out and followed by early cotton; wheat allowed to mature, harvested and followed by late cotton sown between October and December; and grain sorghum (Sorghum bicolor (L.) Moench.) followed by cotton. Land preparation was by minimum tillage and traffic was restricted to the furrows between the beds. Rainfall runoff and soil erosion were monitored with water-height recorders, flumes and troughs. Soil structure was evaluated as air-filled porosity of oven-dried soil in the 0–0.15, 0.15–0.30, 0.30–0.45 and 0.45–0.60m depths. Soil chemical properties measured in the 0–0.15m depth were organic carbon, pH (in 0.01M CaCl2), electrical conductivity (EC1:5) of a 1:5 soil:water suspension and exchangeable Ca, Mg, K and Na. In comparison with 1m beds, 2m beds resulted in lower runoff and soil erosion, lower exchangeable Na, exchangeable sodium percentage and higher EC1:5/exchangeable Na, higher rate of soil organic matter decrease and better soil structure in the 0–0.15m depth. Runoff and erosion were reduced, and cotton lint yields increased either by cropping systems sown early to intercept most of the seasonal rainfall or by those which produced a high level of ground cover. Soil physical and chemical properties were best, and runoff and erosion lowest with 2m beds and cropping systems producing a high level of ground cover.