Field case-Australia

Field-case: Phosphorous and Nitrogen use in Australia

Australia is the second driest continent after Antartica.  Such a dry climate impacts on salt leaching and bedrocking and leads to having shallow soils and fragile hydrologic conditions.

  Fig. 1. Land use in Australia

Three broad zones can be visualized in Australia:

1. conserved or protected uncultivated areas
2. livestock grazing areas with occassional wheat or other grain production depending on market prices and
3. dryland or irrigated agricultural areas (Fig. 1).  

To encourage economic and agricultural development, Australia subsidized irrigation, nitrogen and phosphate fertilizers between 1966 and 1984 (Hyberg, 1991).  Whereas these subsidies facilitated intensive agricultural systems, the overuse of fertilizers lead to increased salinity problems, soil acidity, and contaminated fresh and ground water in the 1980s.   By the 1990s and with reduced pasture areas, the introduction of break crops (ex. Canola) in between cereal croppings, and the adoption of semi-dwarf cultivars, Australia has been experiencing a selective increase in nitrogen applications with a fluctuating upward trend for phosphorous applications (Fig. 2).

Although fertilisers have boosted Australia’s agricultural production, there is a general concern about the impacts of these fertilisers on the environment and aquatic ecosystems.   For example, during the manufacturing of phosphorous, a by-product, known as phosphogypsum which contains radium, is produced.  In addition, due to the persistence of trace metal contaminants at higher concentrations, phosphorous application affects off-site water quality.  By far, the most important environmental concern reported is the export of 5% of the applied phosphorous into surface waters and to a lesser extent groundwater (Nash 2004).  For nitrogen what are the concerns?

 Fig. 2. Tonnes of Nitrogen (N), Phosphorous (P), and Potassium (K) provided as fertilizers in Australia between 1983 and 2005.

The water is considered degraded if the phosphorous level is 0.05mg/L.  On many farms, the phosphorous concentration in soil water can exceed 1mg/L.
How phosphorous export potential is currently measured?
The Olsen and Colwell P tests are the two most common agronomic soil tests available to measure soil phosphorous.  Both use Bicarbonate solutions to extract phosphorous, however, Olsen P test is shorter (30 min) and measures both quantity and concentration of phosphorous in soil whereas colwell P test measures only the quantity and is longer (16 hours).  Unfortunately, none of these tests measure the flow or rate of dissolved phosphorous by water.

Is there any potential for a biosentinel plant here?

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