Microbial Biomass Carbon (MBC)

AUS-TMI-AGR-SMB General Moderate confidence

Benchmark Value

150 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 16 benchmarks together — the OptimalRange form drives the primary score, while 15 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

Therefore, an MBC value of approximately 150 mg/kg is proposed as a lower critical threshold for this context. Below this level, the agroecosystem is considered to be in a degraded state, with impaired ecological function and resilience.

Metric Definition:

Microbial Biomass Carbon (MBC) is the mass of carbon held within the living component of soil organic matter.

Benchmark Definition:

This benchmark defines the lower critical threshold of Microbial Biomass Carbon below which soil ecological function is significantly impaired in agricultural crop production systems in the Tropical & Subtropical Maritime Islands biome of Australia.

Justification:

The proxy data from the Pampas trial provides a strong basis for defining such a threshold. The Permanent Fallow and Low Intensity cropping systems yielded MBC values of 144 mg/kg and 147 mg/kg, respectively, indicating a severely degraded, carbon-limited state.

Sources (1)

Preview of Farming systems can affect soil biology, soil pathogens and system ...

Farming systems can affect soil biology, soil pathogens and system ... Journal

Farming systems can affect soil biology, soil pathogens and system resilience - Grains Research and Development Corporation (GRDC)

View Source

Supporting Sources (7)

Additional references from the underlying research that informed this benchmark.

Australia's bioregions (IBRA) - DCCEEW, accessed July 15, 2025

Contextual Support

Interim Biogeographic Regionalisation for Australia (IBRA), Version 7 (Regions)

View Source

Food, Climate & Regenerative Farming FAQ - The Nature Conservancy, accessed May 11, 2025,

Contextual Support

Scaling Regenerative Agriculture in Tropical Regions - Rainforest Alliance, accessed July 23, 2025

View Source

Hunt and Gather the Island way. - Norfolk Island Stories, accessed July 27, 2025,

Contextual Support

Norfolk Island Environmental Assessment Executive Summary, accessed July 28, 2025

View Source

Lord Howe Island - Wikipedia, accessed July 30, 2025,

Contextual Support GreyLiterature

Lord Howe Island - Wikipedia

View Source

Microbial Biomass Carbon - NSW | Fact Sheets | soilquality.org.au, accessed August 5, 2025,

Contextual Support GreyLiterature

www.soilquality.org.au

View Source

Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate

Contextual Support Journal

Meat & Livestock Australia. (n.d.). Tool 2.8: Soil nutrient critical limits. Meat & Livestock Australia.

View Source

Preview of Traditional Aboriginal and Torres Strait Islander Land Management Practices: Fire-Stick Farming and Beyond - Welcome To Country - Shop, accessed July 28, 2025

Traditional Aboriginal and Torres Strait Islander Land Management Practices: Fire-Stick Farming and Beyond - Welcome To Country - Shop, accessed July 28, 2025

Contextual Support GreyLiterature

Traditional Aboriginal and Torres Strait Islander Land Management Practices: Fire-Stick Farming and Beyond - Welcome To Country - Shop, accessed July 28, 2025

View Source

Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Agricultural Crop Production
Assessment Not Stated
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 4 Jun 2026

Notes

This threshold indicates a severely degraded state with impaired ecological function and resilience. It is approximately 64% lower than the Perennial Pasture benchmark. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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