Soil pH — Benchmark Detail - Nature Index

Benchmark Value

5.5 pH

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 8 benchmarks together — the OptimalRange form drives the primary score, while 7 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary OptimalRange Guard MinimumOnly Guard MaximumOnly Guard MinimumOnly Guard MaximumOnly Guard OptimalRange Guard OptimalRange Guard

Evidence & Context

The research identifies a critical lower threshold for soil function at approximately pH(w) 5.5 (pH(CaCl₂) 4.8), below which aluminium toxicity severely impairs root health and nutrient cycling.

Metric Definition:

Soil pH measured in a 1:5 soil-to-water solution (pH(w)) indicating acidity/alkalinity affecting soil function.

Benchmark Definition:

This benchmark represents the critical lower soil pH threshold below which soil function is impaired due to aluminium toxicity in tropical agricultural crop production systems.

Justification:

Below this level, soluble aluminium directly damages plant roots, phosphorus availability plummets due to fixation, and key microbial functions like nitrogen fixation are inhibited.

Sources (1)

Preview of Agriculture Victoria. (2024). Soil acidity.

Agriculture Victoria. (2024). Soil acidity. Government

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

Supporting Sources (27)

Additional references from the underlying research that informed this benchmark.

Preview of 'Shannon Vale Station'- Weed control without herbicides - Soils For Life, accessed July 16, 2025,

'Shannon Vale Station'- Weed control without herbicides - Soils For Life, accessed July 16, 2025,

Contextual Support Journal

'Shannon Vale Station'- Weed control without herbicides - Soils For Life, accessed July 16, 2025,

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.

Preview of 6. LAND CAPABILITY CLASSES ON THE FORTH MAP, accessed July 16, 2025,

6. LAND CAPABILITY CLASSES ON THE FORTH MAP, accessed July 16, 2025,

Contextual Support Journal

The role of active fractions of soil organic matter in physical and chemical fertility of Ferrosols

Preview of A Benchmarking Approach to Assess Soil Health - SHI, accessed August 28, 2025,

A Benchmarking Approach to Assess Soil Health - SHI, accessed August 28, 2025,

Contextual Support GreyLiterature

Soil | Australia state of the environment 2021, accessed July 16, 2025,

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

Preview of Australian Journal of Soil Research, accessed July 16, 2025,

Australian Journal of Soil Research, accessed July 16, 2025,

Contextual Support

Australian Journal of Soil Research, accessed July 16, 2025,

Preview of Comparison of soil analytical methods for estimating plant-available potassium in highly weathered soils - CSIRO Publishing

Comparison of soil analytical methods for estimating plant-available potassium in highly weathered soils - CSIRO Publishing

Contextual Support Journal

EFFECTS OF AGRICULTURAL MANAGEMENT ON SOIL CARBON AND pH IN THE DOUGLAS DALY REGION OF THE NORTHERN TERRITORY, accessed July 16, 2025,

Preview of Discover the Top 6 Benefits of Regenerative Farming in Australia, accessed July 16, 2025

Discover the Top 6 Benefits of Regenerative Farming in Australia, accessed July 16, 2025

Contextual Support Journal

Soil Health: Supporting Rural Industries in the Wet Tropics, accessed August 28, 2025

Preview of Effects of agricultural management on soil carbon and pH in the Douglas Daly region of the Northern Territory - NT (Book), accessed on June 7, 2025

Effects of agricultural management on soil carbon and pH in the Douglas Daly region of the Northern Territory - NT (Book), accessed on June 7, 2025

Contextual Support Journal

General soil science literature and expert synthesis

Preview of Fertilising avocados | Business Queensland, accessed July 16, 2025,

Fertilising avocados | Business Queensland, accessed July 16, 2025,

Direct Evidence Government

Macadamia grower's guide 2022 - nutrition and soil health – part 1: the foundations - NSW Department of Primary Industries, accessed July 16, 2025,

Preview of Living soils in agriculture | TERN Australia, accessed July 25, 2025,

Living soils in agriculture | TERN Australia, accessed July 25, 2025,

Contextual Support Government

Living soils in agriculture | TERN Australia, accessed July 16, 2025,

Preview of Macadamia Grower guide has the answers - Australian Tree Crop Magazine, accessed July 16, 2025,

Macadamia Grower guide has the answers - Australian Tree Crop Magazine, accessed July 16, 2025,

Contextual Support Journal

Macadamia Grower guide has the answers - Australian Tree Crop Magazine, accessed July 16, 2025,

Preview of Macadamia grower's guide 2022 - nutrition and soil health – part 1: the foundations - NSW Department of Primary Industries

Macadamia grower's guide 2022 - nutrition and soil health – part 1: the foundations - NSW Department of Primary Industries

Contextual Support Journal

Macadamia Tree Yield Article by Australian Premium Macadamias, accessed July 16, 2025,

Preview of Managing Soils for Avocado Production and Root Health - Avocadosource.com, accessed July 16, 2025,

Managing Soils for Avocado Production and Root Health - Avocadosource.com, accessed July 16, 2025,

Contextual Support Journal

Considerations for developing and managing macadamia on floodplain soils - NSW Department of Primary Industries, accessed July 16, 2025,

Preview of Northern Rivers Soil Health Card - Perennial Horticulture

Northern Rivers Soil Health Card - Perennial Horticulture

Contextual Support Journal

Know your soils - NQ Dry Tropics, accessed July 16, 2025,

Preview of Regenerative Agriculture—A Literature Review on the Practices and Mechanisms Used to Improve Soil Health - MDPI, accessed August 5, 2025,

Regenerative Agriculture—A Literature Review on the Practices and Mechanisms Used to Improve Soil Health - MDPI, accessed August 5, 2025,

Contextual Support Journal

Regenerative Agriculture—A Literature Review on the Practices and Mechanisms Used to Improve Soil Health - MDPI, accessed July 20, 2025,

Preview of Soil Health for Bananas | Terrain NRM, accessed July 16, 2025,

Soil Health for Bananas | Terrain NRM, accessed July 16, 2025,

Contextual Support Journal

Soil Health for Bananas | Terrain NRM, accessed July 16, 2025,

Preview of Soil Health Program | Boost Sugarcane Productivity, accessed July 18, 2025,

Soil Health Program | Boost Sugarcane Productivity, accessed July 18, 2025,

Contextual Support

National Soil Strategy, accessed July 16, 2025,

Preview of Soil pH | Environment, land and water - Queensland Government, accessed July 16, 2025,

Soil pH | Environment, land and water - Queensland Government, accessed July 16, 2025,

Contextual Support Journal

Soil pH | Environment, land and water - Queensland Government, accessed July 16, 2025,

Preview of Soil pH: a key edaphic factor regulating distribution and functions of bacterial community along vertical soil profiles in red soil of pomelo orchard - PMC, accessed July 16, 2025,

Soil pH: a key edaphic factor regulating distribution and functions of bacterial community along vertical soil profiles in red soil of pomelo orchard - PMC, accessed July 16, 2025,

Contextual Support Journal

Soil pH: a key edaphic factor regulating distribution and functions of bacterial community along vertical soil profiles in red soil of pomelo orchard - PMC, accessed July 16, 2025,

Preview of The Importance of Soil pH for a Thriving Garden, accessed July 16, 2025,

The Importance of Soil pH for a Thriving Garden, accessed July 16, 2025,

Contextual Support Journal

The Importance of Soil pH for a Thriving Garden, accessed July 16, 2025,

Preview of The legacy of intensive agricultural history on the soil health of (sub)tropical landscapes, accessed July 16, 2025,

The legacy of intensive agricultural history on the soil health of (sub)tropical landscapes, accessed July 16, 2025,

Contextual Support

The legacy of intensive agricultural history on the soil health of (sub)tropical landscapes, accessed July 16, 2025,

Preview of Tropical agricultural land management influences on soil microbial communities through its effect on soil organic carbon | Request PDF - ResearchGate, accessed July 16, 2025,

Tropical agricultural land management influences on soil microbial communities through its effect on soil organic carbon | Request PDF - ResearchGate, accessed July 16, 2025,

Contextual Support GreyLiterature

Tropical agricultural land management influences on soil microbial communities through its effect on soil organic carbon | Request PDF - ResearchGate, accessed July 16, 2025,

Preview of TROPICAL SOILS | Terrain NRM, accessed July 16, 2025,

TROPICAL SOILS | Terrain NRM, accessed July 16, 2025,

Contextual Support Journal

A Revegetation Guide for Sub-Tropical Forest - Greening Australia, accessed July 20, 2025,

Preview of Understanding soil pH - Queensland Government publications, accessed July 16, 2025,

Understanding soil pH - Queensland Government publications, accessed July 16, 2025,

Contextual Support Journal

Understanding soil pH - Queensland Government publications, accessed July 16, 2025,

Preview of Understanding soil pH, accessed July 16, 2025,

Understanding soil pH, accessed July 16, 2025,

Contextual Support Journal

Understanding soil pH, accessed July 16, 2025,

Preview of Understanding soil tests for pastures | Soil | Farm management ..., accessed July 7, 2025,

Understanding soil tests for pastures | Soil | Farm management ..., accessed July 7, 2025,

Contextual Support Government

Soil Acidity | Fact Sheets | soilquality.org.au, accessed July 16, 2025,

Context

Region Australia
Biome Tropical & Subtropical Rainforests
Land Use Agricultural Crop Production
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 10 Jun 2026

Notes

This threshold represents a true ecological tipping point validated by Queensland Government's Strategic Cropping Land guidelines requiring pH > 5.0 for functional agriculture. No upper detrimental threshold — higher values are always better up to natural saturation. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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