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Phosphorus losses in surface runoff

Merrin Macrae, Associate Professor at the University of Waterloo in Ontario, Canada opened a conference sponsored by the Michigan Chapter of the Soil and Water Conservation Society and Michigan State University Extension in East Lansing on March 4, A Matter of Balance: Systems Approaches to Managing the Great Lakes Landscapes. Her presentation, “Phosphorus Losses in Surface Runoff and Tile Drainage from Agricultural Fields Using Multiple Conservation Strategies for Phosphorus Management”, summarized the results of work with farmers in southern Ontario in tracking nutrient cycling and water quality impacts from surface runoff and tile drained lands to Lake Erie tributaries.

Compared to tile drainage, surface runoff was a much ‘hotter’ source of P. At one site, surface runoff was only a minor contributor to the total runoff volume, but it was a major contributor to dissolved reactive phosphorus (DRP) loss. Tile drainage contributed most of the total runoff but overland flow carried most of the nutrients. Most of the total annual P loss was particulate P carried by sediment in runoff during snowmelt. The timing of nutrient application and soil test P was important. When commercial P or poultry litter was applied in the fall autumn rains led to spikes in tile drainage P. Late fall and all applications on the frozen ground should be avoided. Very early fall or spring applications carry less risk, particularly subsurface or banded applications. 

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Michigan State University Extension