Nutrient losses from intensively grazed dairy pastures

Page last updated: Wednesday, 17 January 2018 - 1:54pm

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The Greener Pastures project was set up to assist the Australian dairy industry meet the two major challenges in managing high performing pasture systems: maintaining profitability while meeting the expectations of a community that is increasingly sensitive to environmental issues. This page discusses the major findings from a program to measure nutrient losses in surface runoff and leaching into shallow and deep aquifers.

Introduction

Dairy farmers in Western Australia have a long history of being concerned for the environment in which they live and work, from early involvement with Landcare District Committees through to participating in the various programs run in DairyCatch.

They have planted trees, organised soil testing programs, carried out salinity surveys and, more recently, signed up for effluent, nutrient and irrigation water management programs. Many of these programs produce benefits both on and off the farm — they can improve the farm environment, increase farm productivity and reduce nutrient losses to surface and ground water. The wider community has supported farmers with funding from both State and National landcare programs.

The pressure on farmers to demonstrate good environmental management can only increase. Regular algal blooms in some of our major waterways focus the community’s attention on water quality. This leads to demands that land — urban and rural — is managed to reduce nutrient loss.

In some ways, the easy targets have been tackled. These are the point sources of both urban and rural nutrient loss — operations which produce small volumes of effluent containing a high concentration of nutrients. A larger and more difficult source is the diffuse nutrients that leach and runoff from paddocks as a consequence of the necessary application of fertilisers to produce food.

Phosphorus (P) has been the nutrient of most concern in Western Australia but nitrogen (N) is now regarded as the bigger problem for the long term, particularly for intensive grazing industries. Why?

  • High nitrate-N levels in drinking water can cause human health problems
  • High N levels in surface water upset delicate ecological balances
  • Some N-containing compounds are potent greenhouse gasses
  • N is readily leached from most soils
  •  Urine contains a very high concentration of N
  • N fertiliser use has increased rapidly.

The increased use of N fertiliser to intensify pasture production is a worldwide trend, as farmers respond to the persistent cost-price squeeze, and has led to strict nutrient regulation in the EU and parts of the US and New Zealand.

As more governments look at regulation to manage environmental problems caused by nutrient leaching and runoff, it is important that their policies and regulations are based on sound, locally-based science.

An important aim of the Greener Pastures project was to generate scientifically sound data which would ensure that regulation, if thought necessary, would be appropriate for the soils, rainfall pattern and pasture systems found in the south west of Western Australia. Farmers in other regions should satisfy themselves that policies and regulations proposed for their industries are likewise based on locally valid data.

From an environmental perspective, all grazing industries are being increasingly challenged to manage intensive pasture systems that meet the expectations of a community that is increasingly sensitive to environmental issues.

The natural resource management activities of the Greener Pastures project focussed on three main issues:

  • N budget — how much applied N is productively used in the farming system and how much is surplus or eventually ‘lost’ from the system.
  • The fate of the surplus N in our soils — does increasing N use increase the risk of either waterway pollution or deep groundwater resource pollution.
  • How N is lost from our grazing systems — leaching through the soil, surface runoff or lost as gas to the atmosphere.

The project also looked at phosphorus levels in surface runoff and in shallow and deep aquifers.