Soil Phosphorus
Benchmark Value
Scoring Curve
This curve shows how a field measurement for this indicator would score across all available benchmark forms in this context.
Evidence & Context
Based on the complete analysis, the functional range for plant-available phosphorus (Colwell-P) in a best-practice cropping system on a moderate PBI soil can be defined as follows: Lower Critical Boundary: < 20 mg/kg. Below this level, the system is P-deficient, risking compromised crop growth, yield, and overall function. Optimal Range (Best Available Condition): 25–40 mg/kg. This is the target range for a high-functioning, resilient, and sustainable cropping system. It balances productivity with ecological health, supporting robust soil biological activity. Upper Detrimental Boundary: > 45 mg/kg. Levels approaching and exceeding this threshold are associated with a significant decline in ecological health. There is a high risk of disrupting soil biology (especially AMF), inducing other nutrient deficiencies, and increasing the potential for environmentally damaging P loss to waterways.
Plant-available phosphorus measured as Colwell-P in soil.
This benchmark defines the functional range of plant-available phosphorus in a best-practice cropping system on moderate PBI soil, balancing crop productivity and ecological health. Values below 20 mg/kg indicate phosphorus deficiency, while values above 45 mg/kg risk ecological harm.
This benchmark is derived by balancing the agronomic floor required for productivity (~20 mg/kg) with the upper detrimental threshold where ecological damage and environmental risk occur (>45-50 mg/kg).
Sources (2)
RCS Regenerative Grazing Principles - Resource Consulting Services
View SourceAgriculture Victoria. (2025). Understanding soil tests for pastures. Farm Management.
View SourceSupporting Sources (30)
Additional references from the underlying research that informed this benchmark.
Soil phosphorus—crop response calibration relationships and criteria for oilseeds, grain legumes and summer cereal crops grown in Australia - ResearchGate
View SourceForeword: New Directions for Phosphorus Management in Australian Soils and Farming Systems - CSIRO Publishing, accessed August 4, 2025
View Source
How should we manage our soils to increase soil carbon?, accessed May 10, 2026
View Source
Fertilisers and the environment, accessed August 4, 2025
View SourceRoles of Arbuscular Mycorrhizas in Plant Phosphorus Nutrition: Interactions between Pathways of Phosphorus Uptake in Arbuscular Mycorrhizal Roots Have Important Implications for Understanding and Manipulating Plant Phosphorus Acquisition, accessed August 4, 2025
View SourceLudwig, J.A., Bastin, G.N., Chewings, V.H., Eager, R.W., and Liedloff, A.C. (2005). Clearing savannas for use as rangelands in Queensland: Altered landscapes and water-erosion processes. Rangeland Journal, 27(2), 135-149.
View SourceEffect of variable soil phosphorus on phosphorus concentrations in simulated surface runoff under intensive dairy pastures - ResearchGate, accessed August 4, 2025
View SourcePhosphorus Forms and Functions - Soil Management, accessed July 22, 2025
View SourcePhosphorus, Agriculture & The Environment | VCE Publications | Virginia Tech, accessed August 4, 2025
View SourceForeword: New Directions for Phosphorus Management in Australian Soils and Farming Systems - CSIRO Publishing, accessed August 4, 2025,
View SourceContribution of Arbuscular Mycorrhizal Fungi, Phosphate–Solubilizing Bacteria, and Silicon to P Uptake by Plant - PubMed Central, accessed August 4, 2025
View SourceIndicators of Soil Health - AUSVEG, accessed August 4, 2025
View SourceMuddied Waters: The Use of “Residual” And “Legacy” Phosphorus - Graham Sustainability Institute, accessed August 4, 2025
View SourceMycorrhizal fungi / RHS Gardening, accessed August 4, 2025,
View SourcePhosphorus - Tas | Fact Sheets | soilquality.org.au, accessed August 11, 2025,
View SourcePhosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot | Conservation Physiology | Oxford Academic, accessed July 7, 2025,
View Source
Phosphorus nutrition of phosphorus-sensitive Australian native plants: threats to plant communities in a global biodiversity hotspot - PMC
View SourceAustralian dryland soils are acidic and nutrient-depleted, and have unique microbial communities compared with other drylands - PMC, accessed July 22, 2025
View SourcePhosphorus, Agriculture & The Environment | VCE Publications | Virginia Tech, accessed August 4, 2025,
View Source
Regenerative Agriculture Program restoring soil pH case study: Macdonald, Whites Flat/Koppio
View SourceRegenerative agriculture in Australia: the changing face of farming - Frontiers
View SourceRegenerative Phosphorus Management - Agresol - Regenerative ...
View SourceRoles of Arbuscular Mycorrhizas in Plant Phosphorus Nutrition: Interactions between Pathways of Phosphorus Uptake in Arbuscular Mycorrhizal Roots Have Important Implications for Understanding and Manipulating Plant Phosphorus Acquisition, accessed August 4, 2025,
View SourceDo regenerative grazing management practices improve vegetation and soil health in grazed rangelands? Preliminary insights from a space-for-time study in the Great Barrier Reef catchments, Australia - CSIRO Publishing, accessed August 4, 2025
View SourceHarnessing Soil Microbes to Improve Plant Phosphate Efficiency in Cropping Systems, accessed August 4, 2025
View SourceSoil Microorganisms Mediating Phosphorus Availability Update on Microbial Phosphorus - PMC - PubMed Central, accessed August 4, 2025
View SourceTesting for Phosphorus in Soils - Envirolab Services, accessed August 4, 2025
View SourceSoil tests and high phosphorus levels – Sustainable Market Farming, accessed August 4, 2025
View SourceTowards restoration of grassy White and Yellow Box woodlands - understanding soil changes associated with degradation - Virtual Herbarium
View SourceWhy phosphorus is important - NSW Department of Primary Industries
View Source