Microbial Biomass Carbon (MBC)

AUS-TMI-AGR-SMB General Moderate confidence

Benchmark Value

No specific value — see range

Range: 2 to 4 %

Optimal Range: 2 to 4

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. The scoring engine uses 7 benchmarks together — the OptimalRange form drives the primary score, while 6 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard OptimalRange Guard Point Guard OptimalRange Guard Point Guard LowerThreshold Guard

Evidence & Context

In agricultural soils, MQ typically ranges from 1% to 4%. An optimal state under regenerative management would be characterized by a high Microbial Quotient, likely in the range of 2–4% or greater.

Metric Definition:

Microbial Quotient (MQ) is the ratio of Microbial Biomass Carbon to total Soil Organic Carbon (Cmic/Corg).

Benchmark Definition:

The Microbial Quotient (MQ) indicates the proportion of soil organic carbon that is microbial biomass, reflecting soil carbon availability and microbial efficiency in agricultural crop production on tropical maritime islands.

Justification:

MQ is a more robust and transferable indicator of optimal soil microbial function than absolute MBC values due to soil type and climate variability.

Sources (1)

Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate Journal

Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate

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Supporting Sources (7)

Additional references from the underlying research that informed this benchmark.

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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Farming systems can affect soil biology, soil pathogens and system ...

Direct Evidence Journal

Farming system impact on soil biology and functions

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Food, Climate & Regenerative Farming FAQ - The Nature Conservancy, accessed May 11, 2025,

Contextual Support

Food, Climate & Regenerative Farming FAQ - The Nature Conservancy

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Hunt and Gather the Island way. - Norfolk Island Stories, accessed July 27, 2025,

Contextual Support

Norfolk Island Environmental Assessment Executive Summary, accessed July 28, 2025

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Lord Howe Island - Wikipedia, accessed July 30, 2025,

Contextual Support GreyLiterature

Lord Howe Island - Wikipedia, accessed August 1, 2025,

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Microbial Biomass Carbon - NSW | Fact Sheets | soilquality.org.au, accessed August 5, 2025,

Contextual Support GreyLiterature

Microbial Biomass | Fact Sheets | soilquality.org.au, accessed July 18, 2025,

View Source

Preview of Traditional Aboriginal and Torres Strait Islander Land Management Practices: Fire-Stick Farming and Beyond - Welcome To Country - Shop, accessed July 28, 2025

Traditional Aboriginal and Torres Strait Islander Land Management Practices: Fire-Stick Farming and Beyond - Welcome To Country - Shop, accessed July 28, 2025

Contextual Support GreyLiterature

Traditional Aboriginal and Torres Strait Islander Land Management Practices: Fire-Stick Farming and Beyond - Welcome To Country - Shop, accessed July 28, 2025

View Source

Context

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

Lifecycle

Status Retired
Version 1
Effective From 19 Mar 2026
Effective To 20 Mar 2026

Notes

General guidance suggests an attainable MBC can be up to 5% of total SOC; the 2-4% MQ range indicates efficient carbon cycling under regenerative management. No upper detrimental threshold is identified.

Related Benchmarks

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