Microbial Biomass Carbon (MBC)

AUS-AMR-FOR-SMB General Moderate confidence

Benchmark Value

630 mg/kg

Range: 450 to 700 mg/kg

Optimal Range: 450 to 700

Direction: Higher is desirable ↑

Form: Point

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 5 benchmarks together — the OptimalRange form drives the primary score, while 4 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard Point Guard LowerThreshold Guard OptimalRange Guard

Evidence & Context

The derived benchmark for the topsoil (0–10 cm) is 630 mg/kg.

Metric Definition:

Microbial Biomass Carbon (MBC) is the measure of the carbon contained within the living soil microbial organisms.

Benchmark Definition:

This benchmark represents the best-on-offer condition of Microbial Biomass Carbon in topsoil (0–10 cm) for the Arid Mountain Ranges & Uplands biome under production forestry, indicating a healthy, biologically active soil system at its attainable potential.

Justification:

The benchmark is derived, not directly measured, from an analogue system representing high ecological function. It is calculated from a Soil Organic Carbon (SOC) value of 1.26% under perennial vegetation, using a standard conversion factor of 5% applicable to Australian soils and an assumed bulk density of 1.3 g/cm³.

Sources (4)

Preview of Global negative effects of nitrogen deposition on soil microbes - PMC, accessed July 25, 2025,

Global negative effects of nitrogen deposition on soil microbes - PMC, accessed July 25, 2025, Journal

Biological Mechanisms May Contribute to Soil Carbon Saturation

Preview of Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed August 28, 2025,

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed August 28, 2025, Government

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed July 18, 2025,

Preview of Microbial Biomass - Qld | Fact Sheets | soilquality.org.au

Microbial Biomass - Qld | Fact Sheets | soilquality.org.au GreyLiterature

Global negative effects of nitrogen deposition on soil microbes - PMC

Preview of The relationship between soil organic carbon and soil surface ...

The relationship between soil organic carbon and soil surface ... Journal

Gilgunia Station - Building Landscape resilience you can bank on - Soils For Life, accessed July 28, 2025,

Supporting Sources (16)

Additional references from the underlying research that informed this benchmark.

Preview of 2.2.1 Soil microbial biomass – C, N, and P - ClimEx Handbook

2.2.1 Soil microbial biomass – C, N, and P - ClimEx Handbook

Contextual Support Journal

2.2.1 Soil microbial biomass – C, N, and P - ClimEx Handbook

Preview of Australia's Framework of Criteria and Indicators - DAFF, accessed July 12, 2025,

Australia's Framework of Criteria and Indicators - DAFF, accessed July 12, 2025,

Contextual Support Government

Soil health and stability monitoring in forests - Natural Resources Commission, accessed July 30, 2025

Preview of Australia's Sustainable Forest Management - DAFF, accessed July 12, 2025,

Australia's Sustainable Forest Management - DAFF, accessed July 12, 2025,

Contextual Support

Sustainable forest management: the Australian context - DAFF, accessed July 12, 2025,

Preview of Australian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands - PMC, accessed August 5, 2025,

Australian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands - PMC, accessed August 5, 2025,

Contextual Support Journal

Root Structure and Functioning for Efficient Acquisition of Phosphorus: Matching Morphological and Physiological Traits

Preview of Bulk Density - Measurement | Fact Sheets | soilquality.org.au, accessed August 9, 2025,

Bulk Density - Measurement | Fact Sheets | soilquality.org.au, accessed August 9, 2025,

Methodology Source Government

Bulk Density - Measurement | Fact Sheets | soilquality.org.au, accessed July 26, 2025,

Preview of CO₂ sink to source: Arid Australia's climate and rainfall driven tipping points

CO₂ sink to source: Arid Australia's climate and rainfall driven tipping points

Contextual Support Journal

NVIS Fact sheet MVG 19 – Tussock grasslands, accessed May 19, 2025,

Preview of Coarse woody debris reduces the rate of moisture loss from surface soils of cleared temperate Australian woodlands - CSIRO Publishing

Coarse woody debris reduces the rate of moisture loss from surface soils of cleared temperate Australian woodlands - CSIRO Publishing

Contextual Support Journal

Coarse woody debris reduces the rate of moisture loss from surface soils of cleared temperate Australian woodlands - CSIRO PUBLISHING | Soil Research, accessed August 28, 2025,

Preview of Is there any harmful effect of agrochemicals use on soil microorganisms? - ResearchGate

Is there any harmful effect of agrochemicals use on soil microorganisms? - ResearchGate

Contextual Support GreyLiterature

Starting / Enhancing Your Regenerative Agriculture Journey, accessed August 13, 2025,

Preview of Land | State of the Environment Report 2011

Land | State of the Environment Report 2011

Contextual Support Journal

Australian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands - PMC, accessed August 28, 2025,

Preview of Predicting and regulating soil carbon in a warmer world | TERN Australia, accessed July 6, 2025,

Predicting and regulating soil carbon in a warmer world | TERN Australia, accessed July 6, 2025,

Contextual Support Government

Mapping soil organic carbon fractions for Australia, their stocks, and uncertainty - BG, accessed July 16, 2025,

Preview of Soil condition | NSW State of the Environment

Soil condition | NSW State of the Environment

Contextual Support

Soil condition | NSW State of the Environment

Preview of Soil microbial biomass—what do the numbers really mean? - ResearchGate, accessed August 28, 2025,

Soil microbial biomass—what do the numbers really mean? - ResearchGate, accessed August 28, 2025,

Contextual Support

Soil microbial biomass carbon and CO2? - ResearchGate, accessed July 18, 2025,

Preview of Soil microbial biomass, metabolic quotient, and carbon and nitrogen mineralisation in 25-year-old Pinus radiata agroforestry regimes - CSIRO Publishing

Soil microbial biomass, metabolic quotient, and carbon and nitrogen mineralisation in 25-year-old Pinus radiata agroforestry regimes - CSIRO Publishing

Direct Evidence Journal

Soil microbial biomass, metabolic quotient, and carbon and nitrogen mineralisation in 25-year-old Pinus radiata agroforestry regimes - CSIRO Publishing

Preview of Sustainable Forest Management

Sustainable Forest Management

Contextual Support Journal

Australia's Sustainable Forest Management - DAFF

Preview of Sustainable Forest Management, accessed July 30, 2025,

Sustainable Forest Management, accessed July 30, 2025,

Contextual Support GreyLiterature

Australia's Voluntary National Contribution to the United Nations Global Forest Goals – 2 April 2019

Understanding and quantifying whole soil-profile organic carbon transfer using an environmental tracer - CSIRO Publishing, accessed August 5, 2025,

Contextual Support Journal

Understanding and quantifying whole soil-profile organic carbon transfer using an environmental tracer - CSIRO Publishing

Context

Region Australia
Biome Arid Mountain Ranges & Uplands
Land Use Production Forestry
Assessment Conservation Target
Evidence Type ReferenceCondition

Lifecycle

Status Active
Version 1
Effective From 19 Mar 2026

Notes

Lower Critical Threshold: A sustained MBC level below 200 mg/kg is considered indicative of significant functional impairment, compromising nutrient cycling and soil stability. Optimal Range: Approximately 450–700 mg/kg represents a zone of high ecosystem health and resilience. No upper detrimental threshold — higher values are always better up to natural saturation.

Related Benchmarks

Other benchmarks in the AUS-AMR-FOR-SMB family.