Soil pH
Benchmark Value
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.
Evidence & Context
A Lower Critical Threshold is identified at a soil pH(CaCl₂) of less than 5.0 (approximately equivalent to pH(water) < 5.7), below which aluminium toxicity begins to severely compromise ecosystem function and indicates a degraded, acidified state.
Soil pH measured in a 1:5 soil-to-water solution (pHw) in the topsoil layer (0-10 cm).
This benchmark marks the soil pH level below which aluminium toxicity severely impairs ecosystem function in the biome's protected natural areas.
This threshold is based on scientific literature linking pH(CaCl₂) < 5.0 to aluminium toxicity and ecosystem degradation.
Sources (1)
Soil pH | Environment, land and water - Queensland Government, accessed August 28, 2025,
View SourceSupporting Sources (3)
Additional references from the underlying research that informed this benchmark.
Soil and Landscape Grid National Soil Attribute Maps - pH (Water) (3" resolution) - Release 1. v2
View SourceSoil and Landscape Grid of Australia - CSIRO, accessed August 1, 2025
View SourceThe pH of Australian soils: field results from a national survey - CSIRO Publishing, accessed August 28, 2025,
View Source