Soil pH

AUS-TMS-CON-SPH General High confidence

Benchmark Value

No specific value — see range
Range: 4.6 to 5.3 pH
Thresholds: Lower: 4, Upper: 6.5
Optimal Range: 4.6 to 5.3
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 8 benchmarks together — the OptimalRange form drives the primary score, while 7 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard MinimumOnly Guard OptimalRange Guard OptimalRange Guard LowerThreshold Guard UpperThreshold Guard OptimalRange Guard

Evidence & Context

The pH(CaCl₂) range of 4.6 to 5.3 observed at Litchfield is favored as the core for the benchmark.

Metric Definition:

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

Benchmark Definition:

Reference soil pH benchmark for high environmental health in Australian Tropical Monsoonal Savannas under conservation land use.

Justification:

This range reflects high environmental health in these naturally acidic, nutrient-poor ecosystems. Lower Critical Threshold: pH(CaCl₂) <4.0 is considered critically low, increasing risks of Al/Mn toxicity for a broader range of native flora and impairing essential ecological functions, despite native plant adaptations to acidity. Optimal Range: pH(CaCl₂) 4.5-5.5 supports high biodiversity and thriving natural processes. Upper Detrimental Threshold: pH(CaCl₂) >6.5-7.0 is considered atypical for these naturally acidic soils, potentially leading to nutrient imbalances for acid-adapted native flora and indicating deviation from the natural ecosystem state.

Sources (1)

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, GreyLiterature

Litchfield Savanna BASE Contextual, Soil Physico-Chemical Data ..., accessed May 20, 2025,

View Source

Supporting Sources (26)

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

Soil pH | Environment, land and water - Queensland Government, accessed August 28, 2025,

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

Soil acidity | Soil | Farm management - Agriculture Victoria, accessed August 28, 2025

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

Arnhem Plateau Sandstone Shrubland Complex Ecological Community - listing advice, accessed May 20, 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 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 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
Direct Evidence Journal

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

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

Soils of the Northern Territory factsheet, accessed May 20, 2025

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

Fire regime impacts on soil microbes, soil organic carbon and ground cover in an Australian tropical savanna - CSIRO Publishing, accessed May 11, 2025,

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

Nutrient Cycling in Semi-Arid Grasslands and Savannas: Its Influence on Pattern, Productivity and Stability - UKnowledge, accessed May 20, 2025

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

Improving Soil Structure and pH Levels (DPIFM_NT) - Department of ..., accessed July 20, 2025

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

a comparisonof the soils of tropical latin america ano tropical australia, accessed May 13, 2025,

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

Burning poop: chemical composition and carbon dynamics of large herbivore dung burned in African savanna fires - CSIRO Publishing, accessed May 20, 2025

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

Soils of Cape York Peninsula - Queensland Government publications, accessed May 11, 2025,

View Source

Context

  • Region Australia
  • Biome Tropical Monsoonal Savannas
  • Land Use Conservation / Protected Natural Areas
  • Assessment Conservation Target
  • Evidence Type ReferenceCondition

Lifecycle

  • Status Active
  • Version 1
  • Effective From 25 Mar 2026

Notes

Lower Critical Threshold: 4 pH (CaCl₂). Upper Detrimental Threshold: 6.5 pH (CaCl₂). The benchmark is primarily based on Kandosols in Litchfield National Park and supported by data from other conservation areas and general savanna soil characteristics. The range supports thriving natural processes and biodiversity characteristic of these nutrient-poor environments. [Migration] Original wider evidence range: 4.5 – 5.5 (retained OptimalRange: 4.6 – 5.3)