Microbial Biomass Carbon (MBC)

AUS-TMI-LVG-SMB General Moderate confidence

Benchmark Value

No specific value — see range

Range: 750 to 1000 mg/kg

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 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

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 best available condition for Microbial Biomass Carbon in the topsoil of livestock grazing lands in Australia's Tropical & Subtropical Maritime Islands, reflecting a healthy soil microbial community under sustained, best-practice regenerative management.

Justification:

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%.

Sources (3)

Preview of Regenerative Agriculture—A Literature Review on the Practices and Mechanisms Used to Improve Soil Health - MDPI, accessed August 5, 2025,

Regenerative Agriculture—A Literature Review on the Practices and Mechanisms Used to Improve Soil Health - MDPI, accessed August 5, 2025, Journal

Regenerative Agriculture—A Literature Review on the Practices and Mechanisms Used to Improve Soil Health - MDPI, accessed July 20, 2025,

View Source

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

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

Sparling, G. P. (1992). Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter. Australian Journal of Soil Research, 30(2), 195-207.

View Source

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 - ResearchGate

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

Managing Grazing to Restore Soil Health, Ecosystem Function, and Ecosystem Services - Frontiers

View Source

Soil organic carbon thresholds control fertilizer effects on carbon accrual in croplands worldwide - PMC

Contextual Support Journal

Soil organic carbon thresholds control fertilizer effects on carbon accrual in croplands worldwide - PMC

View Source

Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Livestock Grazing & Pasture
Assessment Not Stated
Evidence Type ReferenceCondition

Lifecycle

Status Active
Version 1
Effective From 5 Jun 2026

Notes

No upper detrimental threshold — higher values are always better up to natural saturation. A lower critical threshold is approximately 300 mg/kg, below which essential soil functions are likely impaired. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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