Microbial Biomass Carbon (MBC)

AUS-ASC-AGR-SMB General Low confidence

Benchmark Value

800 mg/kg

Direction: Higher is desirable ↑

Form: MaximumOnly

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

An upper detrimental threshold is highly speculative (>800-1000 mg C/kg, Very Low confidence), as current literature provides little evidence for negative impacts of high MBC per se in typical mineral agricultural soils.

Metric Definition:

Theoretical MBC level beyond which further increases cease to provide significant additional benefits or could signal negative ecological consequences.

Benchmark Definition:

This benchmark represents a speculative upper limit of microbial biomass carbon in Australian alpine/subalpine mineral agricultural soils, beyond which negative ecological effects might occur, though evidence is very limited.

Justification:

Literature generally supports 'more is better' for MBC up to natural limits; this threshold is a theoretical upper guard.

Sources (2)

Global negative effects of nitrogen deposition on soil microbes - PMC

View Source

Preview of Soil | Australia state of the environment 2021, accessed August 3, 2025,

Soil | Australia state of the environment 2021, accessed August 3, 2025, Government

D11 Control of Erosion and Sedimentation (Design) - Wingecarribee Shire Council

View Source

Supporting Sources (7)

Additional references from the underlying research that informed this benchmark.

Carbon stocks in Tasmanian soils - ResearchGate

Direct Evidence Journal

Carbon stocks in Tasmanian soils - ResearchGate

View Source

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

Contextual Support Government

View Source

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

Direct Evidence Journal

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

View Source

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

Direct Evidence Government

Microbial Biomass | Fact Sheets | soilquality.org.au

View Source

Local Land Services

Direct Evidence Government

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

View Source

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

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

Context

Region Australia
Biome Alpine and Subalpine Complex
Land Use Agricultural Crop Production
Assessment Not Stated
Evidence Type HealthyOperationalRange

Lifecycle

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

Notes

The upper detrimental threshold is speculative and based on theoretical considerations. If MBC consistently exceeds 800-1000 mg/kg and negative impacts occur, further investigation is warranted. AssessmentContext defaulted to 'Not Stated' because the source document did not state one. Pipeline quarantine 2026-06-03c: Rule I — EvidenceStatement explicitly labels the upper threshold as "highly speculative" with "little evidence for negative impacts of high MBC per se." DegradationThreshold/UpperGuard cannot be assigned when document disavows the harm boundary. Changed to HealthyOperationalRange/PrimaryReference. Operator review required. Rejected by operator on 2026-06-03 07:02 UTC

Related Benchmarks

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