Soil pH — Benchmark Detail - Nature Index

Benchmark Value

4.5 pH

Thresholds: Lower: 4.5, Upper: —

Direction: Higher is desirable ↑

Form: LowerThreshold

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

The functional range for ecosystem health is defined by a Lower Critical Threshold of pHCaCl2 4.5, below which toxicity and severe nutrient limitation are likely.

Metric Definition:

Lower Critical Threshold of soil pH measured in 0.01M Calcium Chloride (pHCaCl2)

Benchmark Definition:

This benchmark defines the lower critical pH threshold below which soil toxicity and nutrient limitations likely impair ecosystem health in the Arid Mountain Ranges & Uplands biome.

Justification:

A soil pHCaCl2 below 4.5 is widely recognized as representing a state of high to extreme acidity where elemental toxicities become a major limiting factor for a wide range of plants, including many tolerant species.

Sources (1)

Preview of The pH of Australian soils: field results from a national survey

The pH of Australian soils: field results from a national survey Journal

The pH of Australian soils: field results from a national survey

Supporting Sources (15)

Additional references from the underlying research that informed this benchmark.

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,

Direct Evidence Journal

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

Preview of Al-Beidh, S., & Al-Tawaha, A. R. M. (2023). Basic Properties and Mineralogy of Soils and Their Impact on the Growth of Jarrah Forest in Southwestern Australia. Land, 12(6), 1236.

Al-Beidh, S., & Al-Tawaha, A. R. M. (2023). Basic Properties and Mineralogy of Soils and Their Impact on the Growth of Jarrah Forest in Southwestern Australia. Land, 12(6), 1236.

Contextual Support Journal

Soil Characteristics and Fertility of the Unique Jarrah Forest of Southwestern Australia, with Particular Consideration of Plant Nutrition and Land Rehabilitation - MDPI, accessed July 19, 2025,

Preview of ARID LANDS OF AUSTRALIA - Open Research Repository

ARID LANDS OF AUSTRALIA - Open Research Repository

Contextual Support Government

ARID LANDS OF AUSTRALIA - Open Research Repository

Preview of ARID LANDS OF AUSTRALIA - Open Research Repository, accessed July 15, 2025,

ARID LANDS OF AUSTRALIA - Open Research Repository, accessed July 15, 2025,

Contextual Support Journal

ARID LANDS OF AUSTRALIA - ANU Open Research, accessed July 22, 2025

Preview of Australia - Soils, Climate, Erosion | Britannica

Australia - Soils, Climate, Erosion | Britannica

Contextual Support GreyLiterature

SOIL TESTING, accessed August 1, 2025

Preview of Land | State of the Environment Report 2011

Land | State of the Environment Report 2011

Contextual Support Journal

Australian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands - PMC, accessed August 28, 2025,

Preview of Soil and Landscape Grid National Soil Attribute Maps - pH (Water) (3" resolution) - Release 1

Soil and Landscape Grid National Soil Attribute Maps - pH (Water) (3" resolution) - Release 1

Contextual Support Government

Soil and Landscape Grid National Soil ... - CSIRO Data Access Portal

Preview of Soil and Landscape Grid of Australia - CSIRO

Soil and Landscape Grid of Australia - CSIRO

Methodology Source Government

Soil and Landscape Grid of Australia - CSIRO

Preview of Soil and Landscape Grid of Australia - esoil.io, accessed July 13, 2025

Soil and Landscape Grid of Australia - esoil.io, accessed July 13, 2025

Methodology Source Government

Soil and Landscape Grid of Australia - esoil.io, accessed July 26, 2025,

Preview of Soil Constraints in an Arid Environment—Challenges, Prospects, and Implications - MDPI, accessed July 6, 2025,

Soil Constraints in an Arid Environment—Challenges, Prospects, and Implications - MDPI, accessed July 6, 2025,

Contextual Support Journal

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

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

Preview of TJORITJA / WEST MACDONNELL NATIONAL PARK - Department of Tourism and Hospitality

TJORITJA / WEST MACDONNELL NATIONAL PARK - Department of Tourism and Hospitality

Contextual Support Government

TJORITJA / WEST MACDONNELL NATIONAL PARK - Department of Tourism and Hospitality

Preview of Tool 6.7 Soil health benchmarks and guidelines for managing problem soils

Tool 6.7 Soil health benchmarks and guidelines for managing problem soils

Contextual Support Journal

Tool 6.7 Soil health benchmarks and guidelines for managing problem soils

Preview of Vulkathunha-Gammon Ranges National Park

Vulkathunha-Gammon Ranges National Park

Contextual Support Journal

Vulkathunha-Gammon Ranges National Park

Preview of World salinization with emphasis on Australia | Journal of Experimental Botany

World salinization with emphasis on Australia | Journal of Experimental Botany

Contextual Support Government

World salinization with emphasis on Australia | Journal of Experimental Botany