Microbial Biomass Carbon (MBC)

AUS-TMI-LVG-SMB General Moderate confidence

Benchmark Value

300 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

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:

Critical threshold for Microbial Biomass Carbon (MBC) indicating impaired soil biological function

Benchmark Definition:

This benchmark defines the lower critical threshold of Microbial Biomass Carbon in the topsoil below which soil biological functions are likely critically impaired, indicating degraded soil health in livestock grazing lands of Australia's Tropical & Subtropical Maritime Islands.

Justification:

Derived from international research on soils at risk of desertification and cropland studies, adopting a conservative SOC threshold of 1.5% and a lower-end MBC:SOC ratio of 2.0%.

Sources (2)

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

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

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

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Supporting Sources (4)

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

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

View Source

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,

Direct Evidence Journal

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

View Source

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

Direct Evidence 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.

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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 - ResearchGate

View Source

Context

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

Lifecycle

Status Active
Version 1
Effective From 5 Jun 2026

Notes

Below this level, essential ecosystem services such as nutrient cycling, water retention, and structural stability are likely significantly compromised, indicating a need for restorative intervention. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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