Microbial Biomass Carbon (MBC)

AUS-TSR-LVG-SMB General Moderate confidence

Benchmark Value

1200 mg/kg
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 13 benchmarks together — the OptimalRange form drives the primary score, while 12 guard(s) constrain the result.

Contributing Benchmarks

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

Evidence & Context

This process yields a benchmark of 1200 mg/kg for MBC in the topsoil (0–10 cm).

Metric Definition:

Microbial Biomass Carbon (MBC) represents the total mass of carbon held within the living component of soil organic matter, excluding plant roots and fauna larger than approximately 5×10^3μm3.

Benchmark Definition:

A derived benchmark representing a 'best-on-offer' condition for regeneratively managed livestock pastures in Australia's tropical/subtropical rainforest biome.

Justification:

While the underlying principles and data for both SOC levels in well-managed pastures and the Cmic​:Corg​ ratio are well-established in the scientific literature, the lack of a direct, field-validated measurement from the specific biome and land-use combination necessitates this qualification.

Sources (2)

Preview of Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate
Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate Journal

Meat & Livestock Australia. (n.d.). Tool 2.8: Soil nutrient critical limits. Meat & Livestock Australia.

View Source
Preview of Soil organic matter and carbon sequestration in pastures - FutureBeef, accessed August 5, 2025,
Soil organic matter and carbon sequestration in pastures - FutureBeef, accessed August 5, 2025, GreyLiterature

Sparling, G. P. (1992). Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter. Australian Journal of Soil Research, 30(2), 195-207.

View Source

Supporting Sources (5)

Additional references from the underlying research that informed this benchmark.

Preview of Allen, D. E., Pringle, M. J., Bray, S. G., Hall, T. J., & Dalal, R. C. (2013). What determines soil organic carbon stocks in the grazing lands of north-eastern Australia? Soil Research, 51(8), 695-706.
Allen, D. E., Pringle, M. J., Bray, S. G., Hall, T. J., & Dalal, R. C. (2013). What determines soil organic carbon stocks in the grazing lands of north-eastern Australia? Soil Research, 51(8), 695-706.
Contextual Support Journal

Allen, D. E., Pringle, M. J., Bray, S. G., Hall, T. J., & Dalal, R. C. (2013). What determines soil organic carbon stocks in the grazing lands of north-eastern Australia? Soil Research, 51(8), 695-706.

View Source
Preview of Ingram, J. S. I., & Fernandes, E. C. M. (2001). Managing carbon sequestration in soils: Concepts and terminology. Agriculture, Ecosystems & Environment, 87(1), 111-117.
Ingram, J. S. I., & Fernandes, E. C. M. (2001). Managing carbon sequestration in soils: Concepts and terminology. Agriculture, Ecosystems & Environment, 87(1), 111-117.
Direct Evidence Journal

Ingram, J. S. I., & Fernandes, E. C. M. (2001). Managing carbon sequestration in soils: Concepts and terminology. Agriculture, Ecosystems & Environment, 87(1), 111-117.

View Source
Preview of Microbial Biomass Carbon - NSW | Fact Sheets | soilquality.org.au, accessed August 5, 2025,
Microbial Biomass Carbon - NSW | Fact Sheets | soilquality.org.au, accessed August 5, 2025,
Contextual Support GreyLiterature

www.soilquality.org.au

View Source
Preview of Srivastava, S. C., & Singh, J. S. (1989). Effect of cultivation on microbial biomass C and N of a dry tropical forest soil. Biology and Fertility of Soils, 8(4), 343-348.
Srivastava, S. C., & Singh, J. S. (1989). Effect of cultivation on microbial biomass C and N of a dry tropical forest soil. Biology and Fertility of Soils, 8(4), 343-348.
Contextual Support GreyLiterature

Soil microbial biomass, activity and community composition in adjacent native and plantation forests of subtropical Australia | Request PDF - ResearchGate

View Source
Preview of Xu, X., Schimel, J. P., Thornton, P. E., Song, X., Yuan, F., & Goswami, S. (2017). Substrate and environmental controls on microbial assimilation of soil organic carbon. Soil Biology and Biochemistry, 112, 8-16.
Xu, X., Schimel, J. P., Thornton, P. E., Song, X., Yuan, F., & Goswami, S. (2017). Substrate and environmental controls on microbial assimilation of soil organic carbon. Soil Biology and Biochemistry, 112, 8-16.
Methodology Source Journal

Xu, X., Schimel, J. P., Thornton, P. E., Song, X., Yuan, F., & Goswami, S. (2017). Substrate and environmental controls on microbial assimilation of soil organic carbon. Soil Biology and Biochemistry, 112, 8-16.

View Source

Context

  • Region Australia
  • Biome Tropical & Subtropical Rainforests
  • Land Use Livestock Grazing & Pasture
  • Assessment Not Stated
  • Evidence Type ReferenceCondition

Lifecycle

  • Status Active
  • Version 1
  • Effective From 5 Jun 2026

Notes

Lower Critical Threshold: 200 mg/kg. No upper detrimental threshold — higher values are always better up to natural saturation. Optimal Range: 750 - 2700 mg/kg reflects healthy soil microbial biomass carbon levels in this biome. AssessmentContext defaulted to 'Not Stated' because the source document did not state one.

Related Benchmarks

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

— mg/kg Moderate
Livestock Grazing & Pasture · Not Stated
OptimalRange Active v1