Microbial Biomass Carbon (MBC)

AUS-TMI-LVG-SMB General Moderate confidence

Benchmark Value

300 mg/kg

Thresholds: Lower: 300, Upper: —

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 11 benchmarks together — the OptimalRange form drives the primary score, while 10 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

An MBC value below approximately 300 mg/kg in this biome and land use context suggests that the soil has crossed a critical threshold.

Metric Definition:

Microbial Biomass Carbon (MBC) critical lower threshold in the topsoil (0-10 cm)

Benchmark Definition:

This benchmark defines the critical lower threshold of Microbial Biomass Carbon (MBC) in the topsoil (0-10 cm) below which soil degradation is indicated in Australia's Tropical & Subtropical Maritime Islands biome under livestock grazing.

Justification:

Adopting a conservative Soil Organic Carbon (SOC) lower limit of 1.5% and a conservative MBC:SOC ratio of 2.0%, this threshold is a defensible indicator of soil degradation in this context.

Sources (1)

Critical range of soil organic carbon in southern Europe lands under desertification risk Journal

Critical range of soil organic carbon in southern Europe lands under desertification risk

View Source

Supporting Sources (3)

Additional references from the underlying research that informed this benchmark.

Impacts of Rotational Grazing on Soil Carbon in Native Grass-Based ..., accessed August 5, 2025,

Direct Evidence Journal

Impacts of Rotational Grazing on Soil Carbon in Native Grass-Based Pastures in Southern Australia | PLOS One - Research journals

View Source

Soil organic matter and carbon sequestration in pastures - FutureBeef, accessed August 5, 2025,

Direct Evidence GreyLiterature

A farmer's guide to increasing Soil Organic Carbon under pastures - NSW Department of Primary Industries

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Preview of Synthesis based on: 1) Do regenerative grazing management practices improve vegetation and soil health in grazed rangelands? (Great Barrier Reef Foundation, 2021); 2) Soil organic matter and carbon sequestration in pastures (FutureBeef); 3) Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter (Sparling, 1992).

Synthesis based on: 1) Do regenerative grazing management practices improve vegetation and soil health in grazed rangelands? (Great Barrier Reef Foundation, 2021); 2) Soil organic matter and carbon sequestration in pastures (FutureBeef); 3) Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter (Sparling, 1992).

Contextual Support Journal

Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter (Sparling, 1992)

View Source

Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Livestock Grazing & Pasture
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 19 Mar 2026

Notes

Below this level, essential soil functions such as nutrient cycling, water retention, and structural stability are likely to be significantly compromised, requiring intensive restoration efforts.

Related Benchmarks

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