Soil pH — Benchmark Detail

Benchmark Value

No specific value — see range

Range: 5 to 6.5 pH

Thresholds: Lower: 5, Upper: —

Optimal Range: 5 to 6.5

Direction: Higher is desirable ↑

Form: OptimalRange

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 analysis concludes that an optimal pH range for these ecosystems is between 5.0 and 6.5.

Metric Definition:

Soil pH measured as 1:5 water suspension in topsoil (0-10 cm) in undisturbed tropical rainforest ecosystems.

Benchmark Definition:

This benchmark defines the optimal soil pH range for tropical rainforest soils in conservation areas, indicating healthy acidic conditions essential for native flora and microbial communities.

Justification:

This range is based on multi-site field study of undisturbed rainforest ecosystems in north-eastern Australia, reflecting the natural acidity fundamental to ecosystem health.

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

View Source

Context

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

Lifecycle

Status Active
Version 1
Effective From 24 Mar 2026

Notes

Values below pH 5.0 can induce aluminium toxicity stress; values above 7.5 indicate nutrient imbalances and ecosystem degradation.

Related Benchmarks

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