Managing farm phosphorus losses to catchments

Phosphorus levels in waterways and catchments is a contributing factor to reduced levels of water quality and increased eutrophication. Reducing nutrient loss pathways needs to be a focus for all farmers.

Overview of phosphorus loss pathways

Nutrient losses from farming operations to waterways and catchments are a known source of contamination. Phosphorus losses occur through several pathways. These pathways or modes are defined as –

• Leaching modes: the dissolution of phosphorus in the soil to water flows above or through the soil.
• Physical modes: the loss of P through soil loss due to erosion and detachment (such as stock movement over pastures disturbing soil).
• Intermediate modes: relate to loss or transfer of farm amendments of P such as fertiliser, manure and applied composts.

Practices to reduce losses

Recommended steps to reduce P losses are typically based on the following key points –

• Time your fertiliser applications to avoid periods of intense run-off, and do not apply fertiliser when the soil is saturated, or rain is forecast.
• Place fertiliser within the soil or under surface vegetation and avoid the use of broadcast applications.
• Apply fertilisers as the plants need them by giving several light applications rather than one heavy dose.
• Apply soluble fertiliser through an irrigation system with drippers or low-pressure micro-jets.
• Use stubble mulching, trash blanketing and other methods to protect soils from water and wind erosion to help keep nutrients where they should be (on the paddock, waiting for the next crop or supporting increased pasture growth).
• Consider land forming and the use of contour banks to help reduce the amount of soil and nutrients lost from paddocks.
• Test your soil regularly to assist in determining your soil’s nutrient and trace element requirements and avoid over fertilising.