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Phosphorus Use Efficiency

Baling hay, Sidonia, Victoria.

Phosphorus, nitrogen and potassium are essential elements for all living organisms and key ingredients in fertilizers. Global phosphorus scarcity is likely to threaten the world's ability to meet growing food demand without changes to current phosphorus use (Cordell, D.J., 2010. The story of Phosphorus: sustainability implications of global phosphorus scarcity for food security.  Linkoping University Press, Linkoping, Sweden.).

Despite decades of fertilizer application, many Australian cropping and pasture systems remain phosphorus-deficient due to natural soil deficiencies, sub-optimal fertilizer strategies and soil fixation making phosphorus unavailable to plants. Soil erosion from inappropriate land management practices can wash some applied phosphorus into waterways, polluting the environment.
Where soil phosphorus levels have built up over time to increase pasture production, a proportion of the applied phosphorus becomes sparingly-available to plants, i.e., is "fixed".  Maintaining high production in these soils even under best practice requires the application of more phosphorus than is exported in products (Figure 1).

Phosphorus applied = phosphorus exported + phosphorus accumulated ("fixed") by soil.

Sheep grazing systems typically need to apply five times as much phosphorus via fertilizer as will be exported in product - a phosphorus use efficiency of only 20% (Richard Simpson, pers. comm., 2011).

Fortunately, nutrient management is one of the few farm practices woolgrowers can control to enhance their enterprise profitability.

Phosphorus cycling in a grazing system.

Figure 1: Phosphorus cycling under a grazed pasture scenario (units in kg P/ha/year). Source: Simpson, R. et al, 2007.  Soil biology - some good and bad impacts on pasture production.

Victorian Grasslands Society Conference, Murray Bridge, South Australia.

AWI research investments target more efficient use of both natural and applied soil phosphorus to:

  • Promote efficient use of phosphorus in pastures.
  • Better match soil phosphorus levels to pasture stocking rates.
  • Reduce woolgrowers' cost of production by reducing phosphorus fertilizer input costs.
  • Minimise phosphorus leaching into waterways to reduce the environmental footprint of wool, and biodiversity losses from poor water quality and algal blooms.

Further Information

The Five Easy Steps tool combines years of research, data and information into five steps for woolgrowers to follow when making decisions around an investment in phosphorus.

Up to 30 per cent of soil tests show soil phosphorus (P) levels are above optimum. Many woolgrowers could justifiably decrease P applications without impacting on production.

Five Easy Steps is available to help woolgrowers make more accurate decisions on P applications.  The tool was developed by CSIRO and NSW Department of Primary Industries, with funding from AWI and Pastures Australia members.

Download the Five Easy Steps tool (PDF 1,331Kb) or view more pastures publications.

'Five Easy Steps' publication.