Soil pH — Benchmark Detail

Benchmark Value

7.5 pH

Thresholds: Lower: —, Upper: 7.5

Direction: Lower is desirable ↓

Form: UpperThreshold

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

A detrimental upper threshold exists at pH > 7.5, where nutrient imbalances and nitrogen loss become significant.

Metric Definition:

Soil pH level above which nutrient imbalances and ecosystem degradation occur.

Benchmark Definition:

This benchmark defines the upper soil pH limit beyond which nutrient deficiencies and ecosystem degradation occur in tropical rainforests.

Justification:

Supported by literature on micronutrient availability and nitrogen cycle disruption at high pH.

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 DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 24 Mar 2026

Notes

Values above this threshold indicate a fundamentally altered or degraded rainforest ecosystem.

Related Benchmarks

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