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 15 benchmarks together — the OptimalRange form drives the primary score, while 14 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

A critical lower threshold exists around pH < 5.0, where potential for aluminium toxicity increases.

Metric Definition:

Soil pH level below which aluminium toxicity potential increases.

Benchmark Definition:

Lower critical soil pH threshold indicating onset of aluminium toxicity stress.

Justification:

Supported by field data and ecological understanding of aluminium toxicity effects on rainforest flora.

Sources (1)

Soil and plant nutrient concentrations across a tropical forest-sclerophyll vegetation boundary in north-eastern Australia Journal

Soil and plant nutrient concentrations across a tropical forest-sclerophyll vegetation boundary in north-eastern Australia

View Source

Supporting Sources (2)

Additional references from the underlying research that informed this benchmark.

ASC - VERTOSOLS - Soil Science Australia

Contextual Support

What are the optimum nutrient targets for pastures? - Soil Health Knowledgebase

View Source

Preview of Offord, C. A., & Meagher, P. F. (2014). Light and soil pH have a combined effect on the growth and morphology of the critically endangered Wollemi pine (Wollemia nobilis). AoB Plants, 6, plu011.

Offord, C. A., & Meagher, P. F. (2014). Light and soil pH have a combined effect on the growth and morphology of the critically endangered Wollemi pine (Wollemia nobilis). AoB Plants, 6, plu011.

Contextual Support Journal

Growing up or growing out? How soil pH and light affect seedling growth of a relictual rainforest tree | AoB PLANTS | Oxford Academic, accessed July 20, 2025,

View Source

Context

Region Australia
Biome Tropical & Subtropical Rainforests
Land Use Conservation / Protected Natural Areas
Assessment Pristine Reference
Vegetation Forest
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 8 Jun 2026

Notes

Below this threshold, species intolerant to aluminium toxicity are progressively excluded.

Related Benchmarks

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