Microbial Biomass Carbon (MBC)

AUS-TMI-CON-SMB General Low confidence

Benchmark Value

200 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 9 benchmarks together — the OptimalRange form drives the primary score, while 8 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

A soil with an MBC content of less than 200 mg⋅kg−1 can be considered to have crossed a critical lower threshold.

Metric Definition:

Lower critical threshold of Microbial Biomass Carbon (MBC) below which essential soil functions are significantly impaired.

Benchmark Definition:

This benchmark defines the critical lower limit of microbial carbon in soil below which soil health is severely compromised in tropical forest ecosystems.

Justification:

Field data from degraded tropical dry forests and general soil health literature support this threshold.

Sources (1)

Preview of Derived benchmark based on a triangulated analysis of: 1) "Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests" (Zhang et al., 2009); 2) "Microbial biomass C and N stocks across land uses and soil types in the Brazilian tropical dry forest region" (Menezes et al., 2023); and 3) Established MBC/SOC ratios from "Interpreting Microbial Biomass Carbon" (soilquality.org.au).

Derived benchmark based on a triangulated analysis of: 1) "Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests" (Zhang et al., 2009); 2) "Microbial biomass C and N stocks across land uses and soil types in the Brazilian tropical dry forest region" (Menezes et al., 2023); and 3) Established MBC/SOC ratios from "Interpreting Microbial Biomass Carbon" (soilquality.org.au). Journal

Microbial biomass C and N stocks across land uses and soil types in the Brazilian tropical dry forest region (Menezes et al., 2023)

View Source

Supporting Sources (2)

Additional references from the underlying research that informed this benchmark.

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

Contextual Support GreyLiterature

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au

View Source

Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests (Zhang et al., 2009)

Direct Evidence

Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests (Zhang et al., 2009)

View Source

Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Conservation / Protected Natural Areas
Assessment Pristine Reference
Vegetation Forest
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 5 Jun 2026

Notes

Below this threshold, soil health is significantly compromised, indicating a severely depleted microbial community and loss of biological nutrient cycling capacity.

Related Benchmarks

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