Microbial Biomass Carbon (MBC)

AUS-TGP-AGR-SMB General Moderate confidence

Benchmark Value

150 mg/kg

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 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

Therefore, an MBC level of < 150 mg/kg in the topsoil of a temperate cropping system can be considered critically low.

Metric Definition:

Lower critical threshold of Microbial Biomass Carbon below which soil biological function is impaired.

Benchmark Definition:

A critical lower boundary for Microbial Biomass Carbon indicating impaired soil function in temperate cropping systems.

Justification:

Derived from empirical degraded system data and theoretical SOC threshold calculations.

Sources (2)

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed August 28, 2025, GreyLiterature

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

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Soil organic carbon thresholds control fertilizer effects on carbon accrual in croplands worldwide - PMC Journal

Soil organic carbon thresholds control fertilizer effects on carbon accrual in croplands worldwide - PMC

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Supporting Sources (7)

Additional references from the underlying research that informed this benchmark.

Altered soil microbial community at elevated CO2 leads to loss of soil carbon | PNAS, accessed August 5, 2025

Direct Evidence

Altered soil microbial community at elevated CO2 leads to loss of soil carbon | PNAS

View Source

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

Direct Evidence GreyLiterature

www.soilquality.org.au

View Source

Procedure for Soil Respiration (CO2 Evolution from Rewetting a Dried Soil) - Soil Fertility, accessed July 9, 2025

Direct Evidence GreyLiterature

Tool 6.7 Soil health benchmarks and guidelines for managing ...

View Source

Soil Carbon Sequestration Potential: A review for Australian agriculture - MLA

Contextual Support Journal

Soil Carbon Sequestration Potential: A review for Australian agriculture - MLA

View Source

Soil microbial biomass carbon (SMBC) under different cropping systems... - ResearchGate

Contextual Support Journal

Soil microbial biomass carbon (SMBC) under different cropping systems... - ResearchGate

View Source

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

Direct Evidence 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

Soil microbial biomass, activity and nutrient cycling as indicators of soil health.

Contextual Support GreyLiterature

Soil microbial biomass, activity and nutrient cycling as indicators of soil health., accessed August 5, 2025

View Source

Context

Region Australia
Biome Temperate Grassy Woodlands & Plains
Land Use Agricultural Crop Production
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 4 Jun 2026

Notes

Below this threshold, key microbial functions are likely significantly impaired. No upper detrimental threshold — higher values are always better up to natural saturation. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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