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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Australian Agriculture Assessment 2001
Australian agriculture assessment 2001
National Land and Water Resources Audit, 2001
Appendix 2. Australian Soil Resources Information System
Extractable phosphorus (topsoil - New South Wales and Victoria)
Total phosphorus measures the amount of phosphorus tied up in soil mineral particles and organic matter. Extractable phosphorus attempts to measure the amount of phosphorus that will be available for plants to use. Since phosphorus is essential for plant growth and most plants need more than 0.002% (the average natural level in Australian soils), addition of phosphate fertilisers is required to maximise production.
Many different methods have been used to extract phosphorus and they may give different estimates.
How does it vary and what is it related to?
Most Australian soils contain < 0.002% extractable phosphorus (% by weight or g phosphorus per 100 g of soil). Extractable phosphorus is a function of complex interrelations between pH, soil minerals, organic matter and soil microbes.
Extractable phosphorus is highest in north-western New South Wales, in the Liverpool Plains, and in the Australian Alps across New South Wales and Victoria. It is almost non-existent in coastal New South Wales and in the Victorian mallee region. It is average for Australian soils over most of the remaining area.
Mapping of extractable phosphorus in topsoil can be used to identify areas where the natural fertility of soils is low, and how much fertiliser would be required for crop production.
Table A8 Extractable phosphorus (%) - New South Wales and Victoria* by percent of land use type.
| 0 - 0.002% | 0.003 - 0.005% | > 0.005% | Total land use class area (ha) | |
|---|---|---|---|---|
| Conservation and natural environments | 92 | 7 | 1 | 14 300 700 |
| Production from native environments | 70 | 24 | 6 | 61 472 700 |
| Cropping | 91 | 8 | 0 | 8 812 300 |
| Grazing modified pasture | 97 | 3 | 1 | 7 836 500 |
| Horticulture | 97 | 2 | 0 | 151 100 |
| Irrigated cropping | 82 | 16 | 2 | 621 900 |
| Irrigated modified pasture | 99 | 1 | 0 | 931 100 |
| Total area* | 94 126 300 |
* Area of river basins containing intensive agriculture within Victoria and New South Wales
Level of uncertainty
The model was derived only for Victoria and New South Wales. Estimates of extractable phosphorus are generally more reliable for Murray-Darling Basin and eastern Victoria than coastal New South Wales.
Error diagnostics
| Error diagnostic | Topsoil |
| Number of points used | 2124 |
| R2 | 0.41 |
| Relative error | 0.73 |
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