Soil pH — Benchmark Detail

Benchmark Value

4.8 pH

Thresholds: Lower: 4.8, Upper: —

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 16 benchmarks together — the OptimalRange form drives the primary score, while 15 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

Considering these factors, a lower critical threshold of pH_CaCl2 4.8 is proposed for production forestry in Australian Tropical Monsoonal Savannas.

Metric Definition:

Soil pH measured in 0.01M calcium chloride (pH_CaCl2), below which significant detrimental impacts occur.

Benchmark Definition:

Lower critical soil pH threshold below which Aluminium toxicity and nutrient limitations severely impact plant growth and soil health.

Justification:

Strong and consistent evidence from Australian studies indicating risks of Aluminium toxicity and nutrient limitations below this pH.

Sources (1)

Preview of Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire - CSIRO PUBLISHING | Soil Research, accessed May 16, 2025,

Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire - CSIRO PUBLISHING | Soil Research, accessed May 16, 2025, Journal

Multiple soil element and pH interactions constrain plant performance on tropical soils with a long history of fire - CSIRO PUBLISHING | Soil Research, accessed July 20, 2025

View Source

Supporting Sources (5)

Additional references from the underlying research that informed this benchmark.

(PDF) Soil acidification and natural resource management ..., accessed May 16, 2025,

Contextual Support GreyLiterature

(PDF) Soil acidification and natural resource management ..., accessed May 16, 2025

View Source

(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

Helyar Porter (1989) Soil acidification, its measurement and the processes involved (in S8)

Direct Evidence

Helyar & Porter (1989) Soil acidification, its measurement and the processes involved (in S8)

View Source

Preview of Using digital photography to monitor changes in biocrusts and ground cover in a savanna rangeland - CSIRO Publishing, accessed May 16, 2025,

Using digital photography to monitor changes in biocrusts and ground cover in a savanna rangeland - CSIRO Publishing, accessed May 16, 2025,

Contextual Support Methodology Source Journal

Hunt, L. P., Petty, S., Cowley, R., Fisher, A., Ash, A., & MacDonald, N. (2014). Principles and guidelines for managing cattle grazing in the grazing lands of northern Australia: stocking rates, pasture resting, prescribed fire, paddock size and water points – a review. Rangeland Journal, 36(2), 109-130.

View Source

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 Production Forestry
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 15 Mar 2026

Notes

Lower Critical Threshold: 4.8 pH. Below pH_CaCl2 4.8, severe Al toxicity and nutrient deficiencies occur, impairing root growth and microbial activity. No upper detrimental threshold — higher values are always better up to natural saturation.

Related Benchmarks

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