IMPACT OF SUGAR CANE FARMING PRACTICES ON WATER QUALITY IN THE MACKAY REGION

THE AUSTRALIAN GOVERNMENT’S Reef Rescue Program aims to improve the water quality of the Great Barrier Reef (GBR) lagoon by increasing the adoption of land management practices that reduce the concentrations of nutrients, pesticides and sediment in runoff from agricultural land. Little is known about the water quality benefits of specific sugar cane management practices. To address this, a three year paddock-scale water quality monitoring project commenced in 2009 in the Mackay Whitsunday region as part of the Paddock to Reef Monitoring and Modelling Program. Detailed water quality monitoring sites were established on two sugar cane farms near Mackay in the Sandy Creek catchment. Trials were established on two soil types (Victoria Plains and Marian) to assess the effects of soil management/row spacing, nutrition and herbicide options on water quality, productivity and profitability. Sampling sites were also established at a ‘multi-block’ (~53 ha catchment) and ‘multifarm’ (~3000 ha catchment) scale to determine the water quality changes resulting from expected adoption of improved management practices across a larger area. Water samples collected from runoff were analysed for total suspended solids (TSS), nutrients (total and filtered) and herbicides. Farming practice records and water quality data from block, farm and multi-farm areas will be used for sub-catchment and catchment scale models to predict changes in water quality. Plant cane results show the importance of soil traits, input application rates, the length of time between application and first runoff event and the value of antecedent infiltrating rainfall or irrigation on nutrient/herbicide loss. Higher nitrogen inputs and high background soil phosphorus levels can lead to larger losses of these nutrients. Matching row spacing to machinery track width can reduce runoff. Commercial harvest at both trial sites showed 1.5 m and 1.8 m row spacing treatments produced similar cane yields but that the wider row spacing was more profitable. Relevant management practice information from multiple farms in the sub-catchment was benchmarked