They also found that management practices need to be tailored to local conditions because a solution that works in one area doesn’t in another.
The university’s Londesborough site sits on clay loam, Ilderton on silt loam and Essex on clay.
At Ilderton, the topography “kind of forces the water into the tile” instead of overland, with Londesborough with more slope and tending more to surface runoff.
Both northern sites can usually count on several weeks of snow cover to protect the ground from severe freezing. The Essex site typically loses its snow and leaves the soil susceptible to late-winter hard frosts.
These factors play into the Essex site losing phosphorus consistently year-round, with a higher percentage through the tile.
Londesborough and Ilderton, meanwhile, tend to lose the most through surface runoff during heavy weather events in the spring and fall.
Thus one best management practice (BMP) might work in one location but be less effective in another, they said.
Student James Cober found that “Cover crops are a net benefit for this landscape,” said Dr. Merrin Macrae of the University of Waterloo’s Department of Geography and Environmental Management who headed the study.
Also important is recognizing diversity within the Lake Erie watershed, which Grand River headwaters near Dundalk to the flatlands of Essex and Kent Counties and the hills of southwestern Ohio.
Some Ohio evidence shows increased phosphorus runoff is an unintended consequence of no-till cropping but Macrae believes differences in hydrology and the on-farm method for applying nutrients are contributing factors.
The Ontario site is less hilly and the farmer applies nutrients in bands, something Macrae advises since it removes nutrients from the natural flow path of runoff water.
She agreed leaving a broadcasted layer of manure on untilled land on the university’s Essex site could cause phosphorus runoff but that’s not a suggested BMP.
“If you are going to broadcast manure, if you can incorporate it gently, it is a good idea,” she said.
At other locations, “a return to tillage might actually increase runoff so we’re not always comparing apples to apples.”