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
Phosphorus management thresholds are dictated by soil texture and Phosphorus Buffering Index (PBI), where sandy soils with extremely low PBI (<35–70) reach a detrimental threshold for leaching and runoff when Colwell-P levels moderately exceed agronomic optimums (>30–40 mg/kg) due to minimal retention capacity. In contrast, loamy to clayey soils with moderate to high PBI (>140) have a greater capacity to immobilize phosphorus, yet they still face risks of surface runoff and long-term saturation when Colwell-P consistently exceeds 50–70 mg/kg—a level representing unnecessary accumulation beyond the requirement for 95% relative yield plus a reasonable buffer for ongoing fixation. Ultimately, the governing scientific principle is that any phosphorus accumulation significantly exceeding what the crop and soil system can effectively utilize and retain under best management practices increases long-term environmental risk, regardless of the soil’s initial buffering capacity.
Colwell-P test measurement of plant-available soil phosphorus in the top 0-10 cm soil layer.
This benchmark defines the upper detrimental threshold range of plant-available soil phosphorus in the top 0-10 cm soil layer for Tropical Monsoonal Savannas under agricultural crop production, indicating levels above which environmental risks increase due to phosphorus leaching and runoff.
Exceeding these levels, particularly on a sustained basis, indicates an accumulation of P beyond what the agroecosystem can efficiently use and safely retain, leading to increased environmental risk (e.g., eutrophication) or potential in-field ecological imbalances. The risk is higher and occurs at lower absolute P values in low PBI, sandy soils.
Sources (1)
Soil phosphorus–crop response calibration relationships and criteria for winter cereal crops grown in Australia - CSIRO Publishing
View SourceSupporting Sources (3)
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.