Soil pH — Benchmark Detail - Nature Index

Benchmark Value

No specific value — see range

Range: 7.5 to 8.5 pH

Thresholds: Lower: —, Upper: 9

Optimal Range: 7.5 to 8.5

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.

Evidence & Context

Reference value 2 functional best available condition: pH 7.5 to 8.5 (water).6

Metric Definition:

Soil pH measured in 1:5 soil:water suspension

Benchmark Definition:

This benchmark represents the functional best available soil pH range for agricultural soils on calcareous-derived soils (such as atoll sands) in the Tropical & Subtropical Maritime Islands biome. It reflects the natural alkaline condition under which sustainable crop production operates, focusing on adaptation rather than pH correction.

Justification:

This is not presented as a universally ideal crop-production pH, but as the real-world alkaline condition under which sustainable production must operate. Best practice focuses on adaptation and mitigation through soil organic matter, water management, and crop choice rather than wholesale pH correction.

Sources (2)

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PACIFIC ATOLL SOILS: CHEMISTRY, MINERALOGY AND CLASSIFICATION BY R. J. MORRISON - Smithsonian Institution, accessed July 25, 2025, Journal

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Supporting Sources (34)

Additional references from the underlying research that informed this benchmark.

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(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,

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Anna Biesty - Restoring soil health and preventing flooding on the Norfolk coast, accessed July 25, 2025,

Contextual Support GreyLiterature

Anna Biesty - Restoring soil health and preventing flooding on the Norfolk coast, accessed July 25, 2025,

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Australia – Sub-tropical – temperate - Earthdive, accessed July 25, 2025,

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Australia state of the environment 2021: land, accessed May 11, 2025

Contextual Support Journal

Management Standards and Procedures for timber harvesting operations in Victoria’s State forests

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Australia's bioregions (IBRA) - DCCEEW, accessed July 15, 2025

Contextual Support

Interim Biogeographic Regionalisation for Australia (IBRA), Version 7 (Regions), accessed July 12, 2025,

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Australian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands - PMC, accessed August 5, 2025,

Contextual Support Journal

Root Structure and Functioning for Efficient Acquisition of Phosphorus: Matching Morphological and Physiological Traits

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Christmas Island National Park - DCCEEW, accessed July 30, 2025,

Contextual Support Journal

Christmas Island National Park - DCCEEW, accessed August 2, 2025

Preview of Effects of soil pH on the growth, soil nutrient composition, and rhizosphere microbiome of Ageratina adenophora - PMC - PubMed Central, accessed July 30, 2025,

Effects of soil pH on the growth, soil nutrient composition, and rhizosphere microbiome of Ageratina adenophora - PMC - PubMed Central, accessed July 30, 2025,

Contextual Support Journal

Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations

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How regenerative farming practices are revolutionising biodiversity in agriculture - Institute of Sustainability Studies, accessed July 25, 2025,

Contextual Support GreyLiterature

Grazing support programs | Environment, land and water - Queensland Government, accessed July 28, 2025,

Preview of Impacts of human activity on tropical soil quality in relation to future land productivity and biodiversity, May 2008 - Digital Commons @ USF - University of South Florida, accessed July 25, 2025,

Impacts of human activity on tropical soil quality in relation to future land productivity and biodiversity, May 2008 - Digital Commons @ USF - University of South Florida, accessed July 25, 2025,

Contextual Support Direct Evidence

Impacts of human activity on tropical soil quality in relation to future land productivity and biodiversity, May 2008 - Digital Commons @ USF - University of South Florida, accessed July 25, 2025,

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Land management in horticulture industries | Business Queensland, accessed July 25, 2025,

Contextual Support Government

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Management and conservation of tropical acid soils for sustainable crop production, accessed July 25, 2025,

Contextual Support Journal

Management and conservation of tropical acid soils for sustainable crop production, accessed July 25, 2025,

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Contextual Support Journal

Norfolk Island Food Supply, accessed July 25, 2025,

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Norfolk Island, accessed July 25, 2025,

Contextual Support Journal

Norfolk Island, accessed July 25, 2025,

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Preventing and managing erosion | Environment, land and water | Queensland Government, accessed July 20, 2025,

Contextual Support Government

Erosion & Sediment Control Guide for Building Sites - Clearwater, accessed July 20, 2025

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Reducing Acidity of Tropical Acid Soil to Improve Phosphorus Availability and Zea mays L. Productivity through Efficient Use of Chicken Litter Biochar and Triple Superphosphate - MDPI, accessed July 25, 2025,

Contextual Support Journal

Reducing Acidity of Tropical Acid Soil to Improve Phosphorus Availability and Zea mays L. Productivity through Efficient Use of Chicken Litter Biochar and Triple Superphosphate - MDPI, accessed July 25, 2025,

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Contextual Support GreyLiterature

Regenerative Agriculture - Norfolk FWAG, accessed July 25, 2025,

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

Contextual Support Journal

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Review of crop‐specific tolerance limits to acidity, salinity, and sodicity for seventeen cereal, pulse, and oilseed crops com - UQ eSpace - The University of Queensland, accessed July 25, 2025,

Contextual Support Journal

Review of crop‐specific tolerance limits to acidity, salinity, and sodicity for seventeen cereal, pulse, and oilseed crops com - UQ eSpace - The University of Queensland, accessed July 25, 2025,

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Contextual Support GreyLiterature

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Contextual Support GreyLiterature

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Contextual Support GreyLiterature

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Spatial variability in soil pH and land use as the main influential factor in the red beds of the Nanxiong Basin, China - PubMed Central, accessed July 25, 2025,

Contextual Support Journal

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Contextual Support GreyLiterature

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Contextual Support GreyLiterature

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Contextual Support Government

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Contextual Support Direct Evidence Journal

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Contextual Support GreyLiterature

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Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Agricultural Crop Production
Assessment Pristine Reference
Evidence Type ReferenceCondition

Lifecycle

Status Active
Version 1
Effective From 15 Mar 2026

Notes

Upper Detrimental Threshold: 9 pH. For these systems, best practice involves managing within this inherent alkalinity, not altering it. Functional range is inherently alkaline (pH 7.5-8.5). Lower critical threshold is not applicable due to natural alkalinity.

Related Benchmarks

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