Soil Phosphorus

AUS-TMI-CON-SOP General Moderate confidence

Benchmark Value

No specific value — see range

Range: 15 to 20 mg/kg

Optimal Range: 15 to 20

Direction: Lower is desirable ↓

Form: OptimalRange

Scoring Curve

This curve shows how a field measurement for this indicator would score across all available benchmark forms in this context. The scoring engine uses 8 benchmarks together — the OptimalRange form drives the primary score, while 7 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary OptimalRange Guard MaximumOnly Guard OptimalRange Guard Point Guard OptimalRange Guard OptimalRange Guard MinimumOnly Guard

Evidence & Context

Based on a precautionary synthesis of soil science principles and the known sensitivity of the flora, an available phosphorus level (Colwell P) exceeding 15-20 mg/kg should be considered indicative of an ecosystem at risk of degradation.

Metric Definition:

Available phosphorus (Colwell P) concentration in soil, indicating plant-available phosphorus relevant for ecological health assessment.

Benchmark Definition:

An upper detrimental threshold for available phosphorus in soil, above which ecological degradation is likely in P-sensitive conservation areas.

Justification:

The threshold is precautionary, reflecting the extreme sensitivity of island ecosystems to phosphorus enrichment and the risk of eutrophication leading to loss of native species.

Sources (1)

Preview of Common soil types | Environment, land and water | Queensland ...

Common soil types | Environment, land and water | Queensland ... Government

Phosphorus nutrition of phosphorus-sensitive Australian native ...

View Source

Supporting Sources (5)

Additional references from the underlying research that informed this benchmark.

A simple phosphorus buffering index for Australian soils - ResearchGate

Contextual Support GreyLiterature

(PDF) A simple phosphorus buffering index for Australian soils - ResearchGate

View Source

LORD HOWE ISLAND BOARD On-Site Wastewater Management ...

Contextual Support Journal

LORD HOWE ISLAND BOARD On-Site Wastewater Management ...

View Source

Preview of Phosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot - PMC

Phosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot - PMC

Contextual Support Journal

(PDF) Sensitivity of seedling growth to phosphorus supply in six tree ..., accessed May 15, 2025,

View Source

Soil and Landscape Grid National Soil Attribute Maps - Total Phosphorus (3" resolution) - Release 2 - CSIRO Data Access Portal

Direct Evidence Government

Soil and Landscape Grid National Soil Attribute Maps - Total Phosphorus (3" resolution) - Release 2

View Source

Torres Strait Islands - Wikipedia, accessed July 27, 2025,

Contextual Support GreyLiterature

Torres Strait Islands - Wikipedia

View Source

Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Conservation / Protected Natural Areas
Assessment Conservation Target
Evidence Type DegradationThreshold

Lifecycle

Status Superseded
Version 1
Effective From 24 Mar 2026
Effective To 24 Mar 2026

Notes

No upper detrimental threshold — higher values are always better up to natural saturation. This threshold is significantly lower than agricultural optimum values and is intended to trigger management concern and investigation when exceeded.

Related Benchmarks

Other benchmarks in the AUS-TMI-CON-SOP family.