Soil pH

AUS-AKW-CON-SPH General High confidence

Benchmark Value

8.5 pH
Range: 8 to 8.5 pH
Thresholds: Lower: 7.5, Upper: 8.5
Optimal Range: 8 to 8.5
Direction: Higher is desirable ↑
Form: Point

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 10 benchmarks together — the OptimalRange form drives the primary score, while 9 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary LowerThreshold Guard OptimalRange Guard LowerThreshold Guard UpperThreshold Guard OptimalRange Guard Point Guard LowerThreshold Guard UpperThreshold Guard Point Guard

Evidence & Context

The value of pH 8.5 (H₂O), as measured in the study of soil supporting Atriplex vesicaria 41, stands out as the most compelling and defensible benchmark.

Metric Definition:

Soil pH measured in a 1:5 soil:water suspension, representing the acidity or alkalinity of the soil.

Benchmark Definition:

This benchmark represents the natural, healthy alkaline state of soils in Australia's Arid Karstic Woodlands & Shrublands, dominated by limestone parent material.

Justification:

This value is supported by fundamental chemistry, broad-scale surveys, authoritative reports, and specific field evidence, providing a strong foundation for the benchmark.

Sources (3)

Preview of Arsenic and other elements in saltbush (Atriplex vesicaria) and soils from the goldfields of Western Australia
Arsenic and other elements in saltbush (Atriplex vesicaria) and soils from the goldfields of Western Australia Journal

Arsenic and other elements in saltbush (Atriplex vesicaria) and soils from the goldfields of Western Australia

View Source
Preview of NVIS Fact sheet MVG 22 – Chenopod shrublands, samphire shrublands and forblands - DCCEEW, accessed July 24, 2025
NVIS Fact sheet MVG 22 – Chenopod shrublands, samphire shrublands and forblands - DCCEEW, accessed July 24, 2025 Journal

Some Characteristics of Calcareous soils. A review A.S. Taalab1, G.W. Ageeb2, Hanan S. Siam1 and Safaa A. Mahmoud1 - CURRENT RESEARCH WEB, accessed July 26, 2025,

View Source
Preview of Soil organic matter in cropping systems - NSW Department of Primary Industries, accessed July 22, 2025,
Soil organic matter in cropping systems - NSW Department of Primary Industries, accessed July 22, 2025, Journal

III. WORKING PAPERS - Food and Agriculture Organization of the United Nations, accessed July 26, 2025,

View Source

Supporting Sources (3)

Additional references from the underlying research that informed this benchmark.

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,
Contextual Support Journal

Soil pH | Environment, land and water - Queensland Government, accessed August 28, 2025,

View Source
Preview of Soil Groups of Western Australia - SoilsWest
Soil Groups of Western Australia - SoilsWest
Contextual Support Journal

Soil Groups of Western Australia - SoilsWest

View Source
Preview of The pH of Australian soils: field results from a national survey - CSIRO Publishing, accessed July 25, 2025,
The pH of Australian soils: field results from a national survey - CSIRO Publishing, accessed July 25, 2025,
Contextual Support Journal

The pH of Australian soils: field results from a national survey - CSIRO Publishing, accessed August 28, 2025,

View Source

Context

  • Region Australia
  • Biome Arid Karstic Woodlands & Shrublands
  • Land Use Conservation / Protected Natural Areas
  • Assessment Pristine Reference
  • Evidence Type ReferenceCondition

Lifecycle

  • Status Active
  • Version 1
  • Effective From 24 Mar 2026

Notes

Lower Critical Threshold: 7.5 pH. Upper Detrimental Threshold: 8.5 pH. The ecosystem is defined by its inherent alkalinity, with an optimal range for ecological function identified as pH 8.0 to 8.5 (H₂O). Values above 8.5 indicate sodicity and degraded soil structure.