Microbial Biomass Carbon (MBC)

AUS-AIF-LVG-SMB General Moderate confidence

Benchmark Value

250 mg/kg

Thresholds: Lower: 250, Upper: —

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 11 benchmarks together — the OptimalRange form drives the primary score, while 10 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

A conservative estimate for the lower critical threshold zone can be established at < 250 mg/kg.

Metric Definition:

Microbial Biomass Carbon (MBC) as a measure of microbial carbon in soil.

Benchmark Definition:

This benchmark defines a lower critical threshold for microbial biomass carbon below which soil functions are likely impaired in arid inland floodplains under livestock grazing.

Justification:

This threshold is inferred from studies showing MBC in heavily degraded grazing sites can be 75-85% lower than in healthy controls and from low biological function values in production-focused agricultural systems.

Sources (1)

Preview of grazing impacts on the spatial distribution of soil microbial biomass around tussock grasses in a tropical grassland - Publication : USDA ARS

grazing impacts on the spatial distribution of soil microbial biomass around tussock grasses in a tropical grassland - Publication : USDA ARS Journal

Soil microbial community structure is unaltered by grazing intensity and plant species richness in a temperate grassland steppe in northern China - Publication : USDA ARS, accessed July 29, 2025

View Source

Supporting Sources (2)

Additional references from the underlying research that informed this benchmark.

Loss of Soil Carbon Associated with a Short-Duration Flood in a Semi-Arid Lowland River Floodplain Forest

Contextual Support Journal

Loss of Soil Carbon Associated with a Short-Duration Flood in a Semi-Arid Lowland River Floodplain Forest

View Source

Microbial biomass and microbial biodiversity in some soils from New South Wales, Australia | Request PDF - ResearchGate

Contextual Support Journal

Microbial biomass and microbial biodiversity in some soils from New South Wales, Australia | Request PDF - ResearchGate, accessed July 8, 2025

View Source

Context

Region Australia
Biome Arid Inland Floodplains & Ephemeral River Systems
Land Use Livestock Grazing & Pasture
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 18 Mar 2026

Notes

Soils below this threshold are likely functionally impaired with severely constrained ecosystem processes. ConsistencyResolver applied 2026-03-23 00:20 UTC: UpperThreshold 250 → (check: MaxBelowPointValue, rationale: Clearing UpperThreshold after moving the value to LowerThreshold to reflect the correct threshold direction and allow form auto-correction.) ConsistencyResolver applied 2026-03-23 00:20 UTC: LowerThreshold → 250 (check: MaxBelowPointValue, rationale: The Notes state 'Soils below this threshold are likely functionally impaired,' indicating this is a lower threshold. Moving the value to LowerThreshold aligns with this and will auto-correct the form to MinimumOnly, resolving the contradiction.) [Auto-corrected BenchmarkForm: MaximumOnly → MinimumOnly]

Related Benchmarks

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