Soil pH — Benchmark Detail

Benchmark Value

4.5 pH

Thresholds: Lower: 4.5, Upper: —

Direction: Higher is desirable ↑

Form: LowerThreshold

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 16 benchmarks together — the OptimalRange form drives the primary score, while 15 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

For Australian alpine and subalpine ecosystems under production forestry, a lower critical threshold is proposed at approximately pH 4.5 (1:5 soil:water).

Metric Definition:

Soil pH measured as a 1:5 soil:water suspension

Benchmark Definition:

This benchmark defines the lower critical soil pH threshold below which significant negative impacts on tree health and soil biological processes occur in Australian alpine and subalpine production forestry.

Justification:

Below this pH, significant risks of Al/Mn toxicity, reduced nutrient availability, and impaired microbial activity occur, leading to potential severe decline in tree health and productivity.

Sources (1)

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

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

View Source

Context

Region Australia
Biome Alpine and Subalpine Complex
Land Use Production Forestry
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 24 Mar 2026

Notes

Some natural alpine soil groups have mean pH values below this threshold, indicating adaptation of native vegetation to strong acidity, but these sites are marginal for production forestry.

Related Benchmarks

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