Soil pH

AUS-TMS-CON-SPH General Moderate confidence

Benchmark Value

4 pH (CaCl₂)
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

Based on the available evidence, a pH(CaCl₂) of < 4.0 is proposed as the lower critical threshold for general ecosystem health in Australian Tropical Monsoonal Savannas on soils like Kandosols.

Metric Definition:

Soil pH measured in a dilute electrolyte solution, typically 0.01M calcium chloride (CaCl₂), in topsoil (0-10 cm)

Benchmark Definition:

This benchmark marks the lower critical soil pH threshold below which ecological function in Australian Tropical Monsoonal Savannas may be impaired due to acidity-related stress.

Justification:

This threshold marks a point where the ecosystem may be pushed beyond its natural adaptive range, increasing risks of Al/Mn toxicity and impairing essential ecological functions.

Sources (1)

Preview of Litchfield Savanna BASE Contextual, Soil Physico-Chemical Data 2014 - TERN Data Discovery Portal, accessed May 20, 2025
Litchfield Savanna BASE Contextual, Soil Physico-Chemical Data 2014 - TERN Data Discovery Portal, accessed May 20, 2025 Journal

Litchfield Savanna BASE Contextual, Soil Physico-Chemical Data 2014 - TERN Data Discovery Portal

View Source

Supporting Sources (27)

Additional references from the underlying research that informed this benchmark.

Preview of (PDF) Mineral Nutrition: Tropical Savannas - ResearchGate, accessed May 11, 2025,
(PDF) Mineral Nutrition: Tropical Savannas - ResearchGate, accessed May 11, 2025,
Contextual Support GreyLiterature

(PDF) Mineral Nutrition: Tropical Savannas - ResearchGate, accessed May 20, 2025

View Source
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,
Contextual Support Journal

Caritat, P. de, & Cooper, M. (2011). The pH of Australian soils: Field results from a national survey. Soil Research, 49, 172-182.

View Source
Preview of Adaptive Strategies of Australian Flora - Macquarie University, accessed May 20, 2025
Adaptive Strategies of Australian Flora - Macquarie University, accessed May 20, 2025
Contextual Support Journal

Adaptive Strategies of Australian Flora - Macquarie University, accessed May 20, 2025

View Source
Preview of Agriculture Victoria. (2024). Soil acidity.
Agriculture Victoria. (2024). Soil acidity.
Contextual Support Government

Agriculture Victoria. (2025). Soil acidity. Farm Management.

View Source
Preview of Aluminum stress signaling in plants - PMC - PubMed Central, accessed May 20, 2025
Aluminum stress signaling in plants - PMC - PubMed Central, accessed May 20, 2025
Contextual Support Government

Aluminum stress signaling in plants - PMC - PubMed Central, accessed May 20, 2025

View Source
Preview of Appendix 14. - Northern Territory Government, accessed May 20, 2025
Appendix 14. - Northern Territory Government, accessed May 20, 2025
Contextual Support Journal

Soil Reading - Australian Earth Science Education, accessed May 20, 2025

View Source
Preview of AusEarthed. (n.d.). Soil Reading.
AusEarthed. (n.d.). Soil Reading.
Contextual Support Journal

Victorian Resources Online | Resources | Support and resources ..., accessed July 21, 2025,

View Source
Preview of Calcicole–calcifuge plant strategies limit restoration potential in a regional semi‐arid flora, accessed May 20, 2025
Calcicole–calcifuge plant strategies limit restoration potential in a regional semi‐arid flora, accessed May 20, 2025
Contextual Support Journal

Calcicole–calcifuge plant strategies limit restoration potential in a regional semi‐arid flora, accessed May 20, 2025

View Source
Preview of Can Exclusion of Feral Ecosystem Engineers Improve Coastal Floodplain Resilience to Climate Change? Insight from a Case Study in North East Arnhem Land, Australia - PMC - PubMed Central, accessed May 20, 2025
Can Exclusion of Feral Ecosystem Engineers Improve Coastal Floodplain Resilience to Climate Change? Insight from a Case Study in North East Arnhem Land, Australia - PMC - PubMed Central, accessed May 20, 2025
Irrelevant

Can Exclusion of Feral Ecosystem Engineers Improve Coastal Floodplain Resilience to Climate Change? Insight from a Case Study in North East Arnhem Land, Australia - PMC - PubMed Central, accessed May 20, 2025

View Source
Preview of Chen, X. et al. (2005). Soil organic carbon and nitrogen in northern Australian savannas. Australian Journal of Soil Research, 43(1), 63-71
Chen, X. et al. (2005). Soil organic carbon and nitrogen in northern Australian savannas. Australian Journal of Soil Research, 43(1), 63-71
Contextual Support Journal

Chen, X. et al. (2005). Soil organic carbon and nitrogen in northern Australian savannas. Australian Journal of Soil Research, 43(1), 63-71

View Source
Preview of Comparison of the concentrations of (a, e–j) soil nutrients, (d)... - ResearchGate, accessed May 20, 2025
Comparison of the concentrations of (a, e–j) soil nutrients, (d)... - ResearchGate, accessed May 20, 2025
Methodology Source Journal

Models relating soil pH measurements in water and calcium chloride that incorporate electrolyte concentration | Request PDF - ResearchGate, accessed May 20, 2025

View Source
Preview of Edaphic factors as genetic selection agents and adaptation drivers of native plant species in harsh environments of the - Alice, accessed May 20, 2025
Edaphic factors as genetic selection agents and adaptation drivers of native plant species in harsh environments of the - Alice, accessed May 20, 2025
Contextual Support Journal

Edaphic factors as genetic selection agents and adaptation drivers of native plant species in harsh environments of the - Alice, accessed May 20, 2025

View Source
Preview of hpc.csiro.au, accessed May 20, 2025
hpc.csiro.au, accessed May 20, 2025
Contextual Support

hpc.csiro.au, accessed May 20, 2025

View Source
Preview of Litchfield Savanna BASE Contextual, Soil Physico-Chemical Data ..., accessed May 20, 2025,
Litchfield Savanna BASE Contextual, Soil Physico-Chemical Data ..., accessed May 20, 2025,
Direct Evidence Government

Rance, S.J. et al. (2020). Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire. Soil Research, 58(4), 335-345.

View Source
Preview of Litchfield Savanna SuperSite | Fire Regime Impact - TERN Australia, accessed July 24, 2025,
Litchfield Savanna SuperSite | Fire Regime Impact - TERN Australia, accessed July 24, 2025,
Direct Evidence Government

Land Ecosystem Atmosphere Program (LEAP) - Litchfield Supersite - Resources - The University of Western Australia

View Source
Preview of Liu, X. et al. (2023). Fire regime has a greater impact on soil microbial abundance than on soil organic carbon in a tropical savanna. Wildlife Research.
Liu, X. et al. (2023). Fire regime has a greater impact on soil microbial abundance than on soil organic carbon in a tropical savanna. Wildlife Research.
Contextual Support

Short‐term impact of fire on the total soil microbial and nitrifier communities in a wet savanna

View Source
Preview of Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire | Request PDF - ResearchGate, accessed May 20, 2025
Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire | Request PDF - ResearchGate, accessed May 20, 2025
Contextual Support Journal

Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire | Request PDF - ResearchGate, accessed May 20, 2025

View Source
Preview of Nutrient Cycling in Semi-Arid Grasslands and Savannas: Its Influence on Pattern, Productivity and Stability - UKnowledge, accessed May 20, 2025
Nutrient Cycling in Semi-Arid Grasslands and Savannas: Its Influence on Pattern, Productivity and Stability - UKnowledge, accessed May 20, 2025
Contextual Support

Determinants of soil respiration in a semi-arid savanna ecosystem ...

View Source
Preview of Nutrient limitation in tropical savannas across multiple scales and mechanisms, accessed July 24, 2025,
Nutrient limitation in tropical savannas across multiple scales and mechanisms, accessed July 24, 2025,
Contextual Support Journal

Soil pH | Environment, land and water - Queensland Government, accessed May 20, 2025

View Source
Preview of Nutrient limitation in tropical savannas across multiple scales and mechanisms, accessed May 20, 2025
Nutrient limitation in tropical savannas across multiple scales and mechanisms, accessed May 20, 2025
Contextual Support Journal

ssr150 - Revegetation of mined land in the wet-dry ... - DCCEEW, accessed May 20, 2025

View Source
Preview of Nutrient resorption in tropical savanna forests and woodlands of central Brazil - CSUSM, accessed May 20, 2025
Nutrient resorption in tropical savanna forests and woodlands of central Brazil - CSUSM, accessed May 20, 2025
Contextual Support Journal

Nutrient resorption in tropical savanna forests and woodlands of central Brazil - CSUSM, accessed May 20, 2025

View Source
Preview of Soil pH | Environment, land and water - Queensland Government, accessed July 30, 2025,
Soil pH | Environment, land and water - Queensland Government, accessed July 30, 2025,
Contextual Support Government

Australian dryland soils are acidic and nutrient‐depleted, and have unique microbial communities compared with other drylands - Arid Ecology Lab

View Source
Preview of Soil Quality and Its Management in Humid Subtropical and Tropical Environments - UKnowledge, accessed May 15, 2025,
Soil Quality and Its Management in Humid Subtropical and Tropical Environments - UKnowledge, accessed May 15, 2025,
Contextual Support

Soil Quality and Its Management in Humid Subtropical and Tropical Environments - UKnowledge

View Source
Preview of Test methods a concern with soil aluminium | Groundcover - GRDC Ground Cover, accessed May 20, 2025
Test methods a concern with soil aluminium | Groundcover - GRDC Ground Cover, accessed May 20, 2025
Contextual Support GreyLiterature

Test methods a concern with soil aluminium | Groundcover - GRDC Ground Cover, accessed May 20, 2025

View Source
Preview of Tropical Forests and Grasslands (Savanna) - Soils 4 Teachers, accessed May 20, 2025
Tropical Forests and Grasslands (Savanna) - Soils 4 Teachers, accessed May 20, 2025
Contextual Support Journal

A new detailed map of total phosphorus stocks in Australian soil

View Source
Preview of Understanding soil pH, accessed May 20, 2025
Understanding soil pH, accessed May 20, 2025
Contextual Support Journal

Understanding soil pH, accessed May 20, 2025

View Source
Preview of www.publications.qld.gov.au, accessed May 16, 2025,
www.publications.qld.gov.au, accessed May 16, 2025,
Contextual Support Journal

The Soils of Cape York Peninsula. Cooktown and Weipa Sections. Land Resource Survey and Evaluation.

View Source

Context

  • Region Australia
  • Biome Tropical Monsoonal Savannas
  • Land Use Conservation / Protected Natural Areas
  • Assessment Pristine Reference
  • Evidence Type DegradationThreshold

Lifecycle

  • Status Active
  • Version 1
  • Effective From 10 Jun 2026

Notes

Below this level, there is an increasing likelihood of widespread ecological stress despite native plant adaptations to acidity.

Related Benchmarks

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

— pH (CaCl₂) High
Conservation / Protected Natural Areas · Pristine Reference
OptimalRange Active v1