Soil pH — Benchmark Detail

Benchmark Value

5 pH

Direction: Higher is desirable ↑

Form: MinimumOnly

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 13 benchmarks together — the OptimalRange form drives the primary score, while 12 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

The critical threshold can be set at approximately pH(CaCl₂) 5.0, with severe impacts intensifying as the pH drops below pH(CaCl₂) 4.8.

Metric Definition:

Soil pH measured in calcium chloride solution (pHCaCl₂)

Benchmark Definition:

This benchmark defines the lower critical soil pH threshold below which aluminum toxicity impairs root function and plant growth in the Arid Mountain Ranges & Uplands biome under production forestry.

Justification:

Supported by widespread evidence including national assessments and agricultural extension advice indicating pH(CaCl₂) ≤ 5.5 as acidic and ≤ 4.8 as highly acidic.

Sources (2)

Preview of (PDF) The pH of Australian soils: field results from a national survey - ResearchGate, accessed July 25, 2025,

(PDF) The pH of Australian soils: field results from a national survey - ResearchGate, accessed July 25, 2025, Journal

Caritat, P. de, & Cooper, M. (2011). The pH of Australian soils: Field results from a national survey. Soil Research, 49, 172-182.

View Source

Preview of Private Forestry Guidance Materials, accessed August 1, 2025,

Private Forestry Guidance Materials, accessed August 1, 2025, Journal

Research and advice from the Grains Research and Development Corporation (GRDC) for the South Australian Mallee region

View Source

Supporting Sources (5)

Additional references from the underlying research that informed this benchmark.

Government of South Australia, Department for Environment and Water. (n.d.). Soil Health and Condition.

Direct Evidence Government

Soil acidity - Department for Environment and Water

View Source

Peppermint Box (Eucalyptus odorata) Grassy Woodland of South Australia, accessed August 9, 2025,

Direct Evidence Journal

Northern Mount Lofty Ranges and Southern Flinders Ranges soil descriptions

View Source

Peppermint Box (Eucalyptus odorata) Grassy Woodland of South Australia, accessed July 30, 2025,

Contextual Support GreyLiterature

Peppermint Box (Eucalyptus odorata) Grassy Woodland of South Australia, accessed July 30, 2025,

View Source

Soil acidity is starting to emerge in the Southern Mallee on certain soils types. - GRDC, accessed July 30, 2025,

Direct Evidence

Soil acidity is starting to emerge in the Southern Mallee on certain soils types. - GRDC, accessed July 30, 2025,

View Source

Soil pH - SA | Fact Sheets | soilquality.org.au

Direct Evidence Government

Soil Acidity - NSW | Fact Sheets | soilquality.org.au

View Source

Context

Region Australia
Biome Arid Mountain Ranges & Uplands
Land Use Production Forestry
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 10 Jun 2026

Notes

Below this threshold, aluminum toxicity becomes limiting, leading to poor plant vigor and ecosystem degradation. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

Other benchmarks in the AUS-AMR-FOR-SPH family.