Nutrient export (phosphorus)

John Ruprecht, Department of Agriculture and Food, Western Australia

While phosphorus (P) is a critical plant nutrient for profitable agriculture, its export in surface water run-off or leaching accelerates eutrophication in waterways.

The export of nutrients used in agriculture was assessed as high to very high hazard for most of the coastal catchments.

Algal blooms caused by excessive nutrients and organic matter in waterways are the major cause of fish kills and seagrass losses in rivers and estuaries across the south-west of WA.

Management implications

A range of factors influence P export from agriculture, including fertiliser application method, storage, timing of application, rate applied and source, soil type and texture, slope, paddock fertility, connectivity to drainage, irrigation management, manure disposal and potential for erosion.

Management practices that can reduce P export from paddocks include:

– amending soils to increase low P retention capacity

– using soil testing to inform decisions on fertiliser application rates

– using perennial pastures to increase water and nutrient uptake and decreased erosion

– accurately placing fertiliser

– having fertiliser-free buffer zones close to waterways

– using appropriate fertiliser for the soil type and the plant requirements

– improving irrigation efficiency – replace flood with central pivot irrigation, recycle nutrients within irrigation systems

– improving livestock management around feedlots and dairy sheds, and using effluent to offset nutrient inputs

– licensing of agricultural point sources of nutrient discharge into catchment/estuarine systems

– protecting and revegetating wetlands and waterways

– adopting agricultural best management practices.