Soil pH — Benchmark Detail

Benchmark Value

8.5 pH

Direction: Higher is desirable ↑

Form: MaximumOnly

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 3 benchmarks together — the OptimalRange form drives the primary score, while 2 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard MaximumOnly Guard

Evidence & Context

A pH value greater than 8.5 (H₂O) serves as a robust indicator of a shift from a healthy, calcium-dominated alkaline system to a degraded, sodium-dominated one.

Metric Definition:

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

Benchmark Definition:

This benchmark marks the upper soil pH limit of 8.5, beyond which soil degradation due to sodicity is indicated in the Arid Karstic Woodlands & Shrublands.

Justification:

This threshold is based on scientific literature distinguishing natural alkalinity from detrimental sodicity conditions causing soil structure degradation and reduced ecosystem function.

Sources (1)

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

SOIL pH—SOUTH AUSTRALIA

View Source

Supporting Sources (6)

Additional references from the underlying research that informed this benchmark.

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

Contextual Support 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

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

Direct Evidence Journal

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

View Source

NVIS Fact sheet MVG 22 – Chenopod shrublands, samphire shrublands and forblands - DCCEEW, accessed July 24, 2025

Contextual Support Journal

A Case for Below-Ground Dispersal? Insights into the Biology, Ecology and Conservation of Blind Cave Spiders in the Genus Troglodiplura (Mygalomorphae: Anamidae) - PubMed Central, accessed July 23, 2025

View Source

Soil and Landscape Grid of Australia - esoil.io, accessed July 13, 2025

Direct Evidence Government

UPTAKE OF ARSENIC BY NATIVE PLANTS GROWING ON GOLD TAILINGS IN WESTERN AUSTRALIAN RANGELANDS1

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Soil Groups of Western Australia - SoilsWest

Contextual Support Journal

Soil Groups of Western Australia - SoilsWest

View Source

The pH of Australian soils: field results from a national survey - CSIRO Publishing, accessed July 25, 2025,

Contextual Support Journal

Soil pH Explained - Soil Quality Knowledge Base

View Source

Context

Region Australia
Biome Arid Karstic Woodlands & Shrublands
Land Use Conservation / Protected Natural Areas
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 10 Jun 2026

Notes

Soil pH values exceeding 8.5 indicate sodicity driven by sodium salts, leading to degraded soil structure, reduced water infiltration, and nutrient toxicities/imbalances. This represents a degraded ecosystem state. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

Other benchmarks in the AUS-AKW-CON-SPH family.