Microbial Biomass Carbon (MBC)

AUS-TDG-AGR-SMB General Moderate confidence

Benchmark Value

557 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

The reference value of 557 mg C/kg soil, derived from a well-managed agricultural site in Tintinara, South Australia 21, represents a high achievable state of environmental health for this indicator in the specified context.

Metric Definition:

Microbial Biomass Carbon (MBC) is defined as the total carbon contained within the living cells of microorganisms in the soil, primarily bacteria, fungi, and archaea.

Benchmark Definition:

This benchmark represents a high achievable state of microbial biomass carbon in soils of temperate dry woodlands and native grasslands under agricultural crop production in Australia, indicating good soil microbial health.

Justification:

This value is based on a robust, measured value from a relevant Australian agricultural system and soil type within the target biome, representing a high observed MBC in a temperate dryland context.

Sources (2)

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

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

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

View Source

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

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

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

View Source

Supporting Sources (5)

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

View Source

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)

View Source

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

View Source

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

View Source

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

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,

Direct Evidence Journal

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

View Source

Context

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

Lifecycle

Status Active
Version 1
Effective From 3 Jun 2026

Notes

Lower Critical Threshold: 200 mg/kg. No upper detrimental threshold — higher values are always better up to natural saturation. Supported by average MBC of 338 mg/kg in 35 low-rainfall cropping fields under conservation practices. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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