Microbial Biomass Carbon (MBC)

AUS-TDG-AGR-SMB General Moderate confidence

Benchmark Value

No specific value — see range
Range: 200 to 250 mg/kg
Thresholds: Lower: 200, Upper: 250
Optimal Range: 200 to 250
Direction: Lower 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 7 benchmarks together — the OptimalRange form drives the primary score, while 6 guard(s) constrain the result.

Evidence & Context

In the context of the Temperate Dry Woodlands & Native Grasslands biome, values consistently below 200-250 mg/kg MBC, especially when accompanied by a low MQ (<2-2.5%), likely signify a soil environment where biological functions are substantially limited.

Metric Definition:

Microbial Biomass Carbon (MBC) level below which soil ecological functions are significantly impaired.

Benchmark Definition:

Lower critical threshold for MBC indicating compromised soil biological function.

Justification:

Values below this range are associated with compromised soil biological function and reduced nutrient cycling efficiency.

Sources (2)

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

Farming system impact on soil biology and functions

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Preview of Limitations of soil microbial biomass carbon as an indicator of soil pollution in the field
Limitations of soil microbial biomass carbon as an indicator of soil pollution in the field Journal

The Long-Term Effect of Biochar on Soil Microbial Abundance, Activity and Community Structure Is Overwritten by Land Management - Frontiers

View Source

Supporting Sources (1)

Additional references from the underlying research that informed this benchmark.

Preview of Regenerative opportunities for building soil biological resilience – a ..., accessed May 11, 2025
Regenerative opportunities for building soil biological resilience – a ..., accessed May 11, 2025
Direct Evidence GreyLiterature

Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development - Canadian Science Publishing, accessed August 28, 2025

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Context

  • Region Australia
  • Biome Temperate Dry Woodlands & Native Grasslands
  • Land Use Agricultural Crop Production
  • Assessment Pristine Reference
  • Evidence Type DegradationThreshold

Lifecycle

  • Status Superseded
  • Version 1
  • Effective From 17 Mar 2026
  • Effective To 20 Mar 2026

Notes

Example low MBC value of 147 mg/kg in low-input cropping system supports this threshold.