Assessment of nitrogen mineralising potential of soils in two different landscapes in the Australian sugar industry : Implications for N fertiliser management

Currently, nitrogen fertiliser recommendations in the Australian sugar industry are general in nature, for use across regions and soils. However, differences in soil chemical, physical and pedological properties, within and between the Herbert River and Bundaberg sugar-growing regions have suggested that soils may differ markedly in their ability to mineralise nitrogen during the growing season. Topsoil samples taken from 24 different soil types in the Herbert and seven different soil types in the Bundaberg area were categorised according to the amount of nitrogen mineralised during a two week aerobic incubation. This index, based on easy mineralisable (aerobic) N values, indicates that a large variation in the ability of soils to release N from organic matter is apparent, both within and across the two regions considered. These findings have important implications for nitrogen fertiliser application rates. Lower rates of N applied in certain circumstances could ultimately lead to sugarcane with improved CCS values. In addition, more targeted use of N would minimise off-site etlects associated with fertilisation.