Microbial Biomass Carbon (MBC)

AUS-TDG-AGR-SMB General Moderate confidence

Benchmark Value

200 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

In the context of the Temperate Dry Woodlands & Native Grasslands biome, values consistently below 200-250 mg/kg MBC, especially when accompanied by a low MQ (<2-2.5%), likely signify a soil environment where biological functions are substantially limited.

Metric Definition:

Microbial Biomass Carbon (MBC) is the total carbon contained within the living cells of microorganisms in the soil.

Benchmark Definition:

This benchmark defines a lower critical threshold of microbial biomass carbon below which soil ecological functions are significantly impaired in temperate dry woodlands and native grasslands under agricultural crop production in Australia.

Justification:

Values below 200-250 mg/kg MBC are associated with compromised soil biological function, supported by observed low MBC values in low-input cropping systems.

Sources (1)

$Preview of Long-term land use change in Australia from native forest decreases all fractions of soil organic carbon, including resistant organic carbon, for cropping but not sown pasture - ResearchGate, accessed August 5, 2025,$

Long-term land use change in Australia from native forest decreases all fractions of soil organic carbon, including resistant organic carbon, for cropping but not sown pasture - ResearchGate, accessed August 5, 2025, Journal

Soil microbial activity and litter turnover in native grazed and ungrazed rangelands in semiarid ecosystem - ResearchGate

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Supporting Sources (6)

Additional references from the underlying research that informed this benchmark.

Can soil organic matter be increased in a continuous cropping system in the low to medium rainfall zone? | Birchip Cropping Group

Direct Evidence

(PDF) Soil carbon dynamics under different cropping and pasture management in temperate Australia: Results of three long-term experiments - ResearchGate

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

Contextual Support Journal

Farming systems can affect soil biology, soil pathogens and system resilience - Grains Research and Development Corporation (GRDC)

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Preview of Impact of Management Practices on Soil Organic Carbon Content and Microbial Diversity Under Semi-Arid Conditions - MDPI, accessed July 27, 2025,

Impact of Management Practices on Soil Organic Carbon Content and Microbial Diversity Under Semi-Arid Conditions - MDPI, accessed July 27, 2025,

Contextual Support Journal

Full article: Plant functional traits and soil microbial biomass in different vegetation zones on the Loess Plateau - Taylor & Francis Online

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

Contextual Support GreyLiterature

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

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Limitations of soil microbial biomass carbon as an indicator of soil pollution in the field

Contextual Support Journal

The Long-Term Effect of Biochar on Soil Microbial Abundance, Activity and Community Structure Is Overwritten by Land Management - Frontiers

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Regenerative opportunities for building soil biological resilience – a ..., accessed May 11, 2025

Direct Evidence GreyLiterature

Regenerative opportunities for building soil biological resilience – a case study in the low-rainfall zone in Southern Australia - GRDC

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Context

Region Australia
Biome Temperate Dry Woodlands & Native Grasslands
Land Use Agricultural Crop Production
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 3 Jun 2026

Notes

Low MBC levels linked to insufficient carbon inputs, excessive disturbance, and climatic stress. Example: 147 mg/kg in low-intensity cropping at Iandra NSW. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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