2026 Phosphorus Pools & Fluxes Workshop
February 2026 - Washington, DC
On February 6, 2026, the Agricultural Nutrient Policy Council (ANPC) convened more than 85 researchers, agency officials, agricultural organizations, and water quality professionals to discuss the latest science on phosphorus (P) pools, fluxes, and legacy phosphorus dynamics. The workshop built on the 2024 ANPC workshop and focused on improving understanding of phosphorus sources, movement, storage, and lag times affecting nutrient reduction progress across U.S. watersheds.
The meeting agenda included these topics:
Key Themes:
Persistent phosphorus challenges: National and regional monitoring continues to show slower progress on reducing phosphorus loads compared to nitrogen, raising questions about factors such as legacy P, streambank contributions, hydrologic lag times, and model limitations.
State-led strategies are central: EPA emphasized cooperative federalism and reaffirmed that states are best positioned to lead nutrient loss reduction. Thirty one states now have nutrient reduction strategies underway.
Legacy phosphorus is significant and complex: Legacy P is widespread, slow to deplete, and not fully captured by soil testing or current mass‑balance tools. Understanding “how much,” “where,” and “what form” remains a major scientific need.
Scientific Insights & Research Updates:
Soil & Field-Scale Phosphorus Dynamics
Precision P management and conservation practices are critical levers for reducing losses.
Soil P drawdown, especially where P has accumulated, can substantially reduce losses over time.
Simulation tools (e.g., APLE, APEX, SWAT) can improve planning but require more integration with field measurements.
Grain P testing was identified as an underutilized method to improve P balance accuracy at the farm scale.
Legacy Phosphorus & Watershed Modeling
Legacy P stores—built over decades—drive long lag times between practice adoption and measurable water-quality improvements.
TREND-P and ELEMeNT models show:
Many watersheds have large historical P surpluses.
Only a small fraction of accumulated P is exported each year.
Even with optimal current practices, recovery may take decades.
Urban and domestic P sources (wastewater, food waste) remain important contributors in some basins.
In-Stream & Streambank Contributions
Stream systems act as dynamic sources and sinks of phosphorus.
Streambank erosion contributes 10–67% of total P loads depending on the region.
High intensity rainfall and altered hydrology significantly accelerate bank erosion.
Early research shows streambed sediments actively release and absorb P, and their behavior varies seasonally.
Lag Times & Delivery Delays
New dynamic SPARROW modeling indicates:
Nearly half of U.S. P loads are delivered with a lag of more than one season.
Nutrient storage and delayed release play a larger role than previously modeled.
Seasonal estimates can improve regulatory and management decisions.
Roundtable Takeaways
Better data integration (soil, tile drainage maps, streambank erosion rates, grain P data) is a top need.
Terminology consistency—particularly around “legacy P”—would improve communication across science, policy, and agriculture.
Participants emphasized:
Both in-field and downstream practices are needed; neither alone is sufficient.
Livestock manure handling offers major opportunities for improvement.
Communicating that drawdown is achievable without yield loss is essential for farmer engagement.
Addressing legacy P must not shift blame toward farmers; the issue spans historical practices, hydrology, and urban sources.
Overall Conclusions
Advances in modeling and measurement are improving understanding of phosphorus behavior, but major uncertainties remain—especially regarding the scale and form of legacy P.
Nutrient reduction will require:
Sustained investment in conservation,
Improved manure and fertilizer management,
Strategic in-stream and downstream interventions, and
Continued collaboration among agencies, scientists, and agricultural partners.
The workshop reinforced the importance of realistic timelines, consistent messaging, and coordinated action to support long‑term phosphorus reduction and protect U.S. water quality.
The workshop speakers and attendees are continuing this conversation in a commentary article for the Journal of Soil and Water Conservation's special issue on legacy nutrients. They will also be presenting a symposium at the Soil and Water Conservation Society Annual Meeting in July 2026 and at a special session during the 2026 CANVAS Annual Conference in November.