Microbial Biomass Carbon (MBC)

AUS-TMI-LVG-SMB General Moderate confidence

Benchmark Value

No specific value — see range

Range: 750 to 1000 mg/kg

Thresholds: Lower: 300, Upper: —

Optimal Range: 750 to 1000

Direction: Higher is desirable ↑

Form: OptimalRange

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

The reference value for Microbial Biomass Carbon (MBC) in a high-health livestock grazing system within Australia's Tropical & Subtropical Maritime Island biome is 750 to 1,000 mg/kg in the topsoil (0-10 cm).

Metric Definition:

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

Benchmark Definition:

This benchmark represents the optimal range of Microbial Biomass Carbon (MBC) in the topsoil (0-10 cm) for healthy livestock grazing systems in Australia's Tropical & Subtropical Maritime Islands biome, indicating soil biological activity and health.

Justification:

Confidence in this value is Moderate, as it is derived via a robust synthesis of data from highly relevant mainland analogues (e.g., tropical Queensland grazing lands) rather than from direct measurements on a maritime island. The derivation involves establishing a reference Soil Organic Carbon (SOC) level of 2.5% and applying a scientifically justified MBC:SOC ratio of 3.5%, reflecting high biological activity characteristic of healthy pasture ecosystems.

Sources (1)

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). Journal

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

View Source

Supporting Sources (3)

Additional references from the underlying research that informed this benchmark.

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

Contextual Support Journal

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

View Source

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

View Source

Context

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

Lifecycle

Status Active
Version 1
Effective From 19 Mar 2026

Notes

Lower Critical Threshold: 300 mg/kg. No upper detrimental threshold — higher values are always better up to natural saturation. This range reflects the attainable potential governed by local climate and soil properties.

Related Benchmarks

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