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Reef protection regulations

Impacts of nutrient and pesticide run-off from cane farming

The Great Barrier Reef is Queensland’s most treasured ecosystem and is worth around $6 billion a year to the economy, supporting 69,000 jobs. Strong scientific evidence indicates increased quantities of nutrients and pesticides are entering the Great Barrier Reef lagoon and cane farming is one of the key sources.

How are nutrient and pesticide losses damaging the reef?

Declining marine water quality, influenced by terrestrial runoff, is recognised as one of the most significant threats to the long-term health of the Great Barrier Reef. Pesticides, sediment and nutrient losses are some of the most harmful contributors:

Crown-of-thorns starfish

David-Burdick-NOAA.

Crown-of-thorns starfish

Pesticides pose a risk to aquatic organisms, particularly in freshwater areas and inshore and coastal ecosystems.

Nutrient losses are associated with algal blooms, micro-organisms species shifts and coral-eating crown-of-thorns starfish (COTS) outbreaks across the reef. The current scientific consensus is that nitrogen inputs have a higher correlation with COTS outbreaks than other nutrients such as phosphorus; however all nutrient inputs can contribute to the issue.

On top of this, the cumulative pressure of additional stressors such as extreme rainfall, thermal stress, salinity stress, light stress, cyclone damage and COTS outbreaks can add to the likelihood, prevalence and impacts of coral disease. All of these pressures and stressors impact the reef’s resilience and its recovery following extreme weather events. Good water quality is crucial to improving the reef’s resilience and ability to recover from these pressures.

Reducing the loss of nutrients, sediment and pesticides from your farm will reduce end-of-catchment loads and agricultural chemicals which will help enhance reef resilience in the face of continuing climate change pressures.

How are the nutrients and pesticides from my farm ending up in the reef?

Rainfall run-off and irrigation tail water can wash nutrients, pesticides and sediment into freshwater zones and coastal wetlands. Drainage through agricultural soils can cause leaching of soluble nutrients and pesticides, which infiltrate groundwater and then reach downstream waters.

While nitrogen occurs naturally, an increased amount of fertiliser loss is harming the reef. The best way you can manage its long-term impacts is by better matching nitrogen inputs to the crop requirements and reducing the amount of surplus nitrogen (i.e. the difference between nitrogen inputs and nitrogen taken up by the crop).

How do we know this?

In conjunction with industry through partnership programs, there has been extensive research over 15 years to determine what is contributing to the decline in reef health. The overarching consensus is that key Great Barrier Reef ecosystems are showing declining trends in condition due to continuing poor water quality, cumulative impacts of climate change and increasing intensity of extreme events. The 2013 Scientific Consensus Statement was prepared by a multidisciplinary group of scientists with expertise relevant to Great Barrier Reef water quality, with oversight from the Reef Water Quality Protection Plan Independent Science Panel. It identified that:

  • the main source of excess nutrients, fine sediments and pesticides from Great Barrier Reef catchments is diffuse source pollution from agriculture (see Figure 1)
  • sugarcane is one of the major land uses contributing nitrogen, phosphorus and pesticides to the reef
  • from agricultural sources, the Fitzroy, Burdekin and Wet Tropics regions contribute over 75% to the modelled total nitrogen load to the Great Barrier Reef lagoon from human activity
  • from agricultural sources, the Fitzroy and Burdekin regions contribute approximately 55% to the modelled total phosphorus load to the Great Barrier Reef lagoon from human activity.

Over time, evidence of the link between poor water quality, specifically nutrients, and COTS outbreaks has been greatly strengthened.

Pesticides can pose a high risk to coastal seagrass habitats and freshwater and estuarine wetlands. Concentrations of a range of pesticides have recently exceeded water quality guidelines in many fresh and estuarine water bodies downstream of cropping lands. The Wet Tropics, Burdekin and Mackay Whitsunday regions contribute over 85% of the modelled total photosystem II inhibiting herbicides load to the Great Barrier Reef lagoon from human activity. Sugarcane contributes 94% of this load.

What can I do to reduce nutrient run-off from my farm?

Adopting practices for effective nutrient management can improve farm productivity and profitability and reduce losses to the reef.

Matching nitrogen applications to crop requirements also reduces nitrogen losses. Nutrients from sources such as legumes and mill mud may substantially increase nutrient surpluses and thus have water quality impacts. Using the SIX EASY STEPS™ methodology will help you calculate how much fertiliser to apply including all sources of nutrients.

SIX EASY STEPS™

  1. Know and understand your soils.
  2. Understand and manage nutrient processes and losses.
  3. Regular soil testing.
  4. Adopt soil-specific nutrient management guidelines.
  5. Check on the adequacy of nutrient inputs (e.g leaf analyses).
  6. Monitor and keep good records to modify nutrient inputs when and where necessary.

In a furrow irrigation setting, mill mud applied directly to cane rows, rather than being broadcast or applied to the inter-row, can reduce the amount of nutrients lost (see Figure 1).

In furrow irrigated sugarcane, increasing irrigation efficiency (i.e. reducing over-application of irrigation) also reduces nutrient losses. Efficiencies can be increased by better managing irrigation to crop demand or moving from systems with lower to higher efficiency (e.g. moving from furrow to drip irrigation) (see Figure 2).

How to optimise irrigation on your farm

  1. Use tools (e.g. soil moisture probes, automation and irrigation software) that can help schedule and apply the right amount of irrigation water to match the water holding capacity of the soil.
  2. Drip irrigation or overhead irrigation may have better water use efficiency than furrow irrigation. If you are using a furrow system, consider the shape and length of the furrow for your soil types to minimise deep drainage and run-off.
  3. Recycle pits should be located on suitable soil types and have sufficient free storage to capture run-off.

What can I do to reduce pesticide losses from my farm?

In addition to following the label instructions for pesticides, the most effective way to reduce pesticide losses is to adopt practices for effective pesticide management (see Figure 3).

How to reduce your use of pesticides

  • Use an integrated pest management program (IPM) to control pests over the whole crop cycle
  • Break the disease and pest cycle to prevent spread (e.g. by introducing fallow crop)
  • Retain trash blanket to suppress weeds and reduce herbicides
  • Manage the risk of introducing or spreading pests, weeds and diseases by washing down your equipment
  • Monitor pest levels to ensure management strategies are effective
  • Understand pests, diseases and weeds that are potential problems on your farm and their causes

Effective practices include better managing pesticide application timing (i.e. increasing the time between application and significant rainfall events or irrigation), placement and application method (e.g. banded spraying) (see Figure 4 and 5).

Figure 5

banded sprayer (PDF, 705KB) allows growers to spray herbicides to strategically target weeds, reduce the use of residual herbicides and decrease costs.

How to apply herbicides effectively

  • Monitor weed populations to apply herbicide during early growth.
  • Read the label of the chemical to determine the correct rates, timing or other restrictions.These are usually under ‘general instructions’ or ‘critical comments’ secion of the label.
  • Consider whether residual herbicides are necessary or if knockdown products could achieve the same result.
  • Calibrate the spray rig regualrly. Monitor the presuure gauge and check for leaks.
  • Band spray herbicides using hooded or directed spraying equipment to reduce the use of residuals.

In addition, you should consider taking part in the voluntary Smartcane BMP. This industry developed program is a robust and practical system that is about improving productivity, profitability and sustainability of farm enterprises. Does joining the Smartcane BMP pay off? Read grower case studies to hear their stories.

More information about pesticides, including product selection, is available on our managing agricultural chemicals page.

What are the reef water quality targets?

The Reef Water Quality Protection Plan (Reef Plan), initially established in 2003, is a collaborative program of coordinated projects and partnerships designed to improve the quality of water in the Great Barrier Reef through improved land management in reef catchments. It sets ambitious water quality targets to ensure that by 2020 the quality of water entering the reef from broadscale land use has no detrimental impact on the health and resilience of the Great Barrier Reef.

The Reef Plan was updated in 2009 and 2013. It details specific actions and deliverables to be completed by 2018 when the Reef Plan will be reviewed. In addition, to emphasise Queenslanders’ support for the Great Barrier Reef, and to build on the Reef Plan targets, the Queensland Government has introduced increased commitments.

Water quality targets (2018)

  • At least a 50% reduction in anthropogenic end-of-catchment dissolved inorganic nitrogen loads in priority areas, on the way to achieving up to an 80% reduction in nitrogen by 2025.
  • At least a 20% reduction in anthropogenic end-of-catchment loads of sediment in priority areas, on the way to achieving up to a 50% reduction by 2025.
  • At least 20% reduction in anthropogenic end-of-catchment loads of particulate nutrients in priority areas
  • At least a 60% reduction in end-of catchment pesticide loads in priority areas.

Land and catchment management targets (2018)

  • 90% of sugarcane, horticulture, cropping and grazing lands are managed using best management practice systems (soil, nutrient and pesticides) in priority areas.
  • Minimum 70% late dry season groundcover on grazing lands.
  • The extent of riparian vegetation is increased.
  • There is no net loss of the extent and an improvement in the ecological processes and environmental values of natural wetlands.

Diffuse source pollution is pollution that comes from a wide range of different sources and cannot be directly attributed to one point of dispersal, such as a pipe or waste outlet.

Broadscale land use includes agriculture, such as grazing, cropping, horticulture and forestry, and other ownership of public land (e.g. national parks and reserves).

Urban environments include areas in and around cities and high growth population centres within the Great Barrier Reef catchment.

Licence
Creative Commons Attribution 3.0 Australia (CC BY 3.0)
Last updated
11 April 2017
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