Soil health and nutrient management

The sugarcane area of the Herbert River district is located adjacent to the Great Barrier Reef (GBR). The quality of water entering the GBR lagoon from the Herbert district is one of the most important environmental issues facing the Herbert sugar industry. However, little data on water quality are available from catchments consisting entirely of sugarcane. This project was conducted to establish a number of water quality monitoring sites in relatively small catchments where the land use is solely sugarcane and where individual growers or groups of growers could measure the quality of water in farm drains using simple tools and relate it to their farming practices. Eleven growers volunteered to participate in the programme. They were keen to participate because they felt that sugarcane growers’ reputation of being good custodians of the land had been tarnished by various external studies of water quality and they were eager to demonstrate that their activities were not polluting drainage water. A series of suitable sites for taking and testing water samples were established and V notch weirs were inserted in the drains for the purpose of measuring rates of water flow. A series of simple tools were developed for measuring sediment and nutrients drainage water leaving the farms. An experienced water engineer who had worked in the district for many years agreed to coordinate the project and proceeded to train the growers involved. He also set up and equipped a water analysis laboratory so that the measurements taken by the growers could be validated. Occasional samples were also sent to a NATA accredited laboratory for further validation of the nutrient determinations but also for measurements of pesticide residues. The growers involved in the project have recorded water quality measurements for three years and have also maintained records of on-farm practices that may impact on water quality such as tillage, fertilising, land levelling and herbicide applications and other activities that may impact on water quality. The growers were provided with information on desirable water quality levels. If their measurements exceeded these levels, growers reacted quickly to seek possible explanations for the elevated readings. The project was evaluated at the commencement, mid-term and just before its conclusion. The growers involved developed a list of the critical factors that needed to be achieved in order for the project to be successful. The mid-term evaluation was conducted with members of the Project Consultative Group and the final evaluation was again conducted with the growers involved in the project. Feedback was generally positive but there were a few areas where things could have been improved. The project outcomes consisted largely of improved knowledge, particularly amongst the growers, of what simple techniques are available for measuring nutrients, pH, dissolved oxygen and turbidity of farm drainage water. Growers learnt what constituted high, medium and low levels for the different water quality parameters and developed a better understanding of the relationship between rainfall and discharge characteristics of drains on their farms. They improved their understanding 4 of the relationship between on-farm management practices and water quality and of the accuracy and reliability of the different tools used to measure water quality. An important outcome has been the continued engagement and support of growers involved with the project, and the engagement and support of regulatory and other government support agencies through the project consultative group. This is important for the next phase of the project which aims to expand from 11 growers to around 100 growers conducting water quality monitoring. The existence of a committed nucleus of growers will be essential for helping to inspire others to participate. Likely economic benefits of the project will be increased farm profitability arising from improved farm practices associated with better management of farm inputs such as fertilisers and herbicides. Reduced input costs arising from reductions in soil tillage and more targeted applications of nutrients and herbicides will also contribute. Environmental benefits will arise from improved water quality on farm and in the downstream ecosystem, and improved soil health arising from changes in farming practices. Social benefits will include the empowerment of growers, who are now armed with better information about their farm practices and the likely impacts on water quality; greater confidence amongst growers when interacting with government and environmental groups; and improved attitudes and engagement by growers in sustainable land management.

There is concern about environmental impacts of cropping in catchments of Australia’s Great Barrier Reef, especially losses of nitrogen (N) and herbicides from cropping systems. Sugarcane production in the Burdekin region in the dry tropics stands out from other crops/regions because, (1) it is fully irrigated, which may enhance the losses of any chemicals from farms, and (2) it has the highest N fertiliser application rates of any sugarcane producing region in Australia. There are few measurements of N and/or herbicide losses from sugarcane production, especially fully irrigated production. More complete information is needed to evaluate, develop and underpin the adoption of management practices to reduce environmental impacts of sugarcane production. Four streams of work were undertaken to provide this information: Monitoring water quality leaving sugarcane farms. Demonstrating water quality and productivity benefits of farm management practices. Harnessing the information from these two components to describe and classify management practice systems typical of past, current and future ‘best practice’, and estimate the water quality, productivity and economic benefits of these systems. Communicating results of these activities widely within and beyond the region. Water, N and herbicide losses were measured at three sites in different parts of the Burdekin region, covering a range of soil types and irrigation managements. The experimental data were then used to parameterise the APSIM-Sugarcane cropping systems model, and then used to infill missing data and develop complete water and N balances for each of the three crops measured at the sites. N losses in runoff were relatively small, being less than 10 kg N ha-1 crop-1. Herbicide losses were similar to those measured previously. More N was lost via deep drainage than runoff at all sites, even those with slowly permeable soils. The results were consistent with the known ground water nitrate contamination issues in the region.

Soil health and nutrient management

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