Soil pH

AUS-TSR-CON-SPH General Moderate confidence

Benchmark Value

7.5 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 15 benchmarks together — the OptimalRange form drives the primary score, while 14 guard(s) constrain the result.

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 nitrogen loss indicate ecosystem degradation.

Benchmark Definition:

Upper critical soil pH threshold indicating ecosystem degradation due to alkalinity.

Justification:

Based on literature documenting micronutrient deficiencies and nitrogen cycle disruption at high pH levels.

Sources (1)

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

Preview of ASC - VERTOSOLS - Soil Science Australia
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

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