Microbial Biomass Carbon (MBC)

AUS-ASC-AGR-SMB General Low confidence

Benchmark Value

450 mg/kg

Direction: Higher is desirable ↑

Form: Point

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 Point Guard MinimumOnly Guard OptimalRange Guard Point Guard MinimumOnly Guard Point Guard MinimumOnly Guard OptimalRange Guard Point Guard MinimumOnly Guard OptimalRange Guard Point Guard MinimumOnly Guard OptimalRange Guard MinimumOnly Guard

Evidence & Context

Based on this synthesis, a tentative MBC reference value for the "best available condition" in Australian alpine/subalpine agricultural systems under sustained best-practice regenerative management (0-10 cm) is proposed as 450 mg C/kg dry soil.

Metric Definition:

Microbial Biomass Carbon (MBC) measured in mg C/kg dry soil in the topsoil (0-10 cm), ideally reflecting peak growing season values.

Benchmark Definition:

This benchmark represents the target microbial biomass carbon level in the topsoil of Australian alpine and subalpine agricultural systems under best-practice regenerative management during the peak growing season. It indicates healthy soil microbial activity essential for soil function.

Justification:

The benchmark is derived from upper percentile MBC values in Victorian agricultural soils, estimations from SOC levels in Tasmanian cool-climate soils, and other well-managed Australian agricultural systems.

Sources (6)

Carbon stocks in Tasmanian soils - ResearchGate Journal

Carbon stocks in Tasmanian soils - ResearchGate

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Preview of Farming system legacy impacts on the storage and persistence of soil organic carbon and understanding the different types carbon in northern cropping systems – science that value adds in field farming systems research - GRDC

Farming system legacy impacts on the storage and persistence of soil organic carbon and understanding the different types carbon in northern cropping systems – science that value adds in field farming systems research - GRDC Government

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Global Climate Change Effects on Soil Microbial Biomass Stoichiometry in Alpine Ecosystems - MDPI, accessed August 28, 2025, Journal

Global Climate Change Effects on Soil Microbial Biomass Stoichiometry in Alpine Ecosystems - MDPI

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Preview of Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org ...

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org ... Government

Microbial Biomass | Fact Sheets | soilquality.org.au

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Local Land Services Government

Microbial Biomass Carbon - 0 - 10cm | Victoria | Examine ...

View Source

Preview of Soil microbial biomass—what do the numbers really mean? - ResearchGate, accessed August 28, 2025,

Soil microbial biomass—what do the numbers really mean? - ResearchGate, accessed August 28, 2025, GreyLiterature

Responses of soil labile organic carbon stocks and the carbon pool management index to different vegetation restoration types in the Danxia landform region of southwest China - PMC - PubMed Central

View Source

Supporting Sources (1)

Additional references from the underlying research that informed this benchmark.

ResearchOnline@JCU - James Cook University, accessed on June 7, 2025

Direct Evidence Journal

Variation in soil microbial biomass in the dry tropics: impact of land-use change

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Context

Region Australia
Biome Alpine and Subalpine Complex
Land Use Agricultural Crop Production
Assessment Not Stated
Season peak growing season
Evidence Type ReferenceCondition

Lifecycle

Status Superseded
Version 1
Effective From 3 Jun 2026
Effective To 3 Jun 2026

Notes

Lower Critical Threshold: 200 mg/kg. No upper detrimental threshold — higher values are always better up to natural saturation. The optimal range is 350-700 mg/kg. The benchmark is an aspirational target based on synthesis of multiple sources. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

Other benchmarks in the AUS-ASC-AGR-SMB family.