Microbial Biomass Carbon (MBC)

AUS-TGP-LVG-SMB General Moderate confidence

Benchmark Value

350 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 13 benchmarks together — the OptimalRange form drives the primary score, while 12 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard OptimalRange Guard MinimumOnly Guard Point Guard MinimumOnly Guard OptimalRange Guard Point Guard OptimalRange Guard MinimumOnly Guard Point Guard OptimalRange Guard Point Guard

Evidence & Context

Lower Critical Threshold: A value below approximately 350 mg/kg is identified as a critical threshold.

Metric Definition:

Microbial Biomass Carbon (MBC) level below which essential soil biological functions are significantly compromised.

Benchmark Definition:

This benchmark defines the critical lower threshold of Microbial Biomass Carbon below which soil biological functions are significantly impaired, indicating degradation in temperate grassy woodlands and plains under livestock grazing.

Justification:

Based on significant MBC decline under heavy grazing (~28%) and low Microbial Quotient (<3.5%) indicating poor biological function. Aligns with values from low-rainfall, managed systems.

Sources (2)

Preview of A global meta-analysis of livestock grazing impacts on soil ...

A global meta-analysis of livestock grazing impacts on soil ... Journal

Regenerative opportunities for building soil biological resilience – a ...

View Source

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

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

View Source

Supporting Sources (5)

Additional references from the underlying research that informed this benchmark.

Journal on Protected Mountain Areas Research and Management

Direct Evidence Journal

Development of a new piosphere in arid chenopod shrubland grazed by sheep. I. Changes to the soil surface. - ResearchGate

View Source

Microbe Biomass in Relation to Organic Carbon and Clay in Soil - MDPI, accessed August 28, 2025,

Contextual Support Journal

Forest Soil Microbiomes: A Review of Key Research from 2003 to 2023 - MDPI

View Source

Predicting and regulating soil carbon in a warmer world | TERN Australia, accessed August 28, 2025,

Contextual Support Government

Fact Sheets Soil Organic Carbon Storage in the Western Avon Basin - WA

View Source

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

View Source

Soil carbon stocks under different pastures and pasture management in the higher rainfall areas of south-eastern Australia

Contextual Support Journal

Soil carbon stocks under different pastures and pasture management in the higher rainfall areas of south-eastern Australia

View Source

Context

Region Australia
Biome Temperate Grassy Woodlands & Plains
Land Use Livestock Grazing & Pasture
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 3 Jun 2026

Notes

Levels below this threshold indicate a biologically impoverished and functionally compromised soil ecosystem. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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