Soil Phosphorus
Benchmark Value
Evidence & Context
Proposed Target Operational Range (Colwell-P, mg/kg): For soils with Low to Moderate PBI (e.g., PBI approximately 70-280), which includes many loamy and some clayey Kandosols and Vertosols: 20-35 mg/kg. For soils with Very Low PBI (e.g., PBI approximately 35-70), often sandy loams or soils with lower P-fixing capacity: 15-30 mg/kg. For soils with Extremely Low to Very Very Low PBI (e.g., PBI 35), typically sandy soils with high leaching potential: 10-25 mg/kg.
Soil phosphorus measured as Colwell-P test (0-10 cm depth) representing plant-available phosphorus fractions.
This benchmark defines the target operational range of soil phosphorus in mg/kg for sustainable agricultural crop production in Australian Tropical Monsoonal Savannas, adjusted by soil Phosphorus Buffering Index (PBI) categories to support crop productivity and environmental sustainability.
This PBI-adjusted range aims to support good crop productivity (based on agronomic critical levels for ~90% relative yield) while being managed within a regenerative framework to enhance P use efficiency, build soil organic P, and minimize environmental losses.
Supporting Sources (4)
Additional references from the underlying research that informed this benchmark.
Based on levels indicating severe P deficiency for plant growth and likely impairment of soil ecological functions (e.g., microbial activity, nutrient cycling), drawing from S18, S43, S44, S50 (interpreted for cropping context).
Based on levels where P loss to the environment (leaching/runoff) becomes a significant risk, or where potential for P toxicity or nutrient imbalances may arise. Threshold is highly dependent on soil PBI, texture, and hydrology.
Derived synthesis from 1, S26, S41, S55, S56, S68, with ecological interpretation and adjustment for regenerative principles.
Soil phosphorus–crop response calibration relationships and criteria for winter cereal crops grown in Australia - CSIRO Publishing
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