Microbial Biomass Carbon (MBC)

AUS-TSW-LVG-SMB General Moderate confidence

Benchmark Value

250 mg/kg

Thresholds: Lower: 250, Upper: —

Direction: Lower 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 critical lower threshold, representing a state of degradation, is defined by a syndrome of poor ecological health (e.g., <40% ground cover) and is quantitatively anchored at an MBC value of ≤250 mg/kg.

Metric Definition:

Microbial Biomass Carbon (MBC) represents the total carbon contained within the living cells of soil microorganisms.

Benchmark Definition:

This benchmark defines a critical upper threshold for Microbial Biomass Carbon below which soil health is considered degraded in temperate semi-arid shrublands and open woodlands under livestock grazing.

Justification:

The baseline MBC value of 250 mg/kg measured at the Tamworth site prior to the implementation of improved management serves as a quantitative anchor for this state.

Sources (1)

Sustainable Grazing Systems (SGS) Key Program - Final Report Journal

Sustainable Grazing Systems (SGS) Key Program - Final Report

View Source

Supporting Sources (3)

Additional references from the underlying research that informed this benchmark.

functions-of-soil-organic-matter-and-the-effect-on-soil-properties.pdf.pdf, accessed July 19, 2025,

Contextual Support Journal

The biodiversity cost of carbon sequestration in tropical savanna - PMC - PubMed Central

View Source

Impact of agricultural land use on distribution of microbial biomass and activity within soil aggregates - ResearchGate

Contextual Support Journal

Plant responses to livestock grazing frequency in an Australian temperate grassland, accessed August 8, 2025,

View Source

Preview of Managing grazing to increase ground cover in rangelands: using remote sensing to detect change - CSIRO Publishing, accessed July 18, 2025,

Managing grazing to increase ground cover in rangelands: using remote sensing to detect change - CSIRO Publishing, accessed July 18, 2025,

Contextual Support Journal

Guppy, C.N., Waters, C.M., Hacker, R.B., et al. (2024). Managing grazing to increase ground cover in rangelands: using dynamic regional comparison to document property-scale change. Rangeland Journal.

View Source

Context

Region Australia
Biome Temperate Semi-Arid Shrublands & Open Woodlands
Land Use Livestock Grazing & Pasture
Assessment Pristine Reference
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 20 Mar 2026

Notes

A state of degradation characterized by <40% ground cover, low pasture biomass (<2 t DM/ha), and an MBC value at or below 250 mg/kg. ConsistencyResolver applied 2026-03-23 00:14 UTC: UpperThreshold 250 → (check: MaxBelowPointValue, rationale: Clearing UpperThreshold after moving the value to LowerThreshold to correctly represent this as a MinimumOnly threshold.) ConsistencyResolver applied 2026-03-23 00:14 UTC: LowerThreshold → 250 (check: MaxBelowPointValue, rationale: The Notes state that MBC values at or below 250 mg/kg indicate degradation, which is a lower threshold. Moving the value from UpperThreshold to LowerThreshold will auto-correct the form from MaximumOnly to MinimumOnly, resolving the contradiction.) [Auto-corrected BenchmarkForm: MaximumOnly → MinimumOnly] ConsistencyResolver applied 2026-03-23 00:14 UTC: UpperThreshold 250 → (check: MaxBelowOptimalLow, rationale: Clearing UpperThreshold after moving the threshold value to LowerThreshold to reflect the correct threshold direction and allow form auto-correction.) ConsistencyResolver applied 2026-03-23 00:14 UTC: LowerThreshold → 250 (check: MaxBelowOptimalLow, rationale: The Notes state that MBC values at or below 250 mg/kg indicate degradation, which is a lower threshold. Moving the value from UpperThreshold to LowerThreshold will correct the form from MaximumOnly to MinimumOnly, resolving the contradiction.)

Related Benchmarks

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