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UVM Extension warns of legacy phosphorus, outlines tile‑drainage research and nutrient management work
Summary
UVM Extension described causes of elevated soil phosphorus in some Vermont fields, ongoing tile‑drainage trials at Discovery Acres, and extension work on nutrient management plans, buffers and practices to limit phosphorus transport to waterways including Saint Albans Bay.
Heather Darby, professor and soil specialist at University of Vermont Extension, told a legislative committee that much of Vermont’s soil phosphorus results from long‑term fertilizer and manure applications and that phosphorus binds strongly to aluminum in many hill soils, reducing plant availability and leading farmers historically to apply more phosphorus.
Darby described research at a commercial site called Discovery Acres in St. Albans Bay on Jewett Brook (within a watershed identified as impaired). The site compares tile drainage and non‑tile systems and evaluates best management practices to minimize environmental impacts while maintaining yields. Funding for the site originally came from the Vermont Agency of Agriculture and the Lake Champlain Basin Program, she said.
Darby said phosphorus is relatively immobile in many soils and accumulates over time; it moves off fields mainly attached to eroded soil. She noted that while many Vermont fields are phosphorus‑deficient, concentrated dairy areas with long histories of manure application can have individual fields with high phosphorus; the state’s approach is to manage those fields so levels do not increase and to implement drawdown plans where appropriate.
Darby said mandated buffers, cover cropping, no‑till and nutrient management plans are among the practices used to reduce soil loss and phosphorus transport. She said legacy phosphorus in lake and stream sediments can release over time and contribute to cyanobacteria blooms in places such as St. Albans Bay. Possible remediation approaches mentioned in discussion included targeted alum treatments in confined water bodies, but she said large‑scale remediation is difficult and context‑specific.
Darby emphasized extension education: farmers attend nutrient‑management classes, create farm plans and implement practices tailored to local soil and watershed conditions. She said researchers are developing “strategic tillage” trials to alleviate compaction in no‑till fields in ways that minimize erosion risk.
