Assessing Coastal Plain Risk Indices for Subsurface Phosphorus Loss

Area of Science:

• Environmental Science
• Agricultural Science
• Soil Science

Background:

• Phosphorus (P) Index evaluations are crucial for nutrient management in the U.S.
• Current P Indices inadequately represent subsurface P loss in drained agroecosystems.
• Subsurface flow is the primary P transport pathway in Atlantic Coastal Plain systems.

Purpose of the Study:

• To evaluate subsurface P risk routines of five P Indices.
• To explore methods for assessing P loss via subsurface flow.
• To identify reliable proxies for P loss when water quality data is scarce.

Main Methods:

• Assessed five P Indices using water quality and soil datasets from the Atlantic Coastal Plain.
• Compared P Index risk scores with dissolved P loads in leachate and ditch drainage.
• Investigated soil water extractable P (WEP) at seasonal high water table as a proxy for P loss.

Main Results:

• Subsurface P risk scores showed directional correctness and statistical significance with P loads, but data limitations existed.
• WEP concentrations served as a realistic proxy for subsurface P losses in ditch drainage.
• WEP associations with P risk ratings mirrored those from limited water quality data.

Conclusions:

• WEP is a valuable metric for assessing subsurface P risk when direct water quality data is unavailable.
• Current P Indices require enhancement for subsurface flow representation.
• Long-term monitoring and modeling are essential for robust P Index appraisals.