Researchers defining phosphorus movement in Ontario soils

4R strategy plays a key role in reducing phosphorous runoff

Three short huts with solar panels on them sprout in Bob McIntosh’s wheat field near St. Marys, Ont.

Inside the huts are monitoring equipment that goes right to the tiles that systemically move water from his farm. His farm is one of six across Ontario with the monitoring equipment that allows University of Waterloo researchers to study how water, and especially the phosphorus in it, flows off of farms.

“We’re trying to capture the natural variability in the Ontario landscape,” says Dr. Janina Plach, who is doing post-doctoral research at the University of Waterloo.

It also shows that a significant portion of phosphorus is lost in the non-growing season.

Janina Plach. photo: John Greig

“That’s really a knowledge gap right now, understanding how phosphorus is leaving our soil in Ontario during that non-growing season,” says Plach.

Algal blooms in shallow and warm Lake Erie have been partially blamed on agricultural phosphorus use.

The University of Waterloo research, led by Dr. Merrin Macrae, is showing that there’s a lot to know yet about phosphorus movement in different types of soils before Ontario-specific best management practices are developed.

The long-term work is showing that phosphorus appears to move off of farms in different ways than it does in Ohio, the main American farm-region contributor to phosphorus load in Lake Erie.

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“In Ontario we’re seeing that the phosphorus losses in Ontario are lower than Ohio and we’re losing our phosphorus in the tile drains in a particulate form. In Ohio, we’re seeing higher levels of phosphorus in the tile drains and it is mainly in a soluble reactive form,” says Plach.

Plach says the differences could be related to management, soil texture or geochemistry, and the research going forward will help determine why there are differences.

However, Plach says that farms that use the 4Rs strategy, which certifies agronomists to help advise their customers in order to place nutrients in the right source at the right rate, right time and in the right place, is a best management practice that has shown to be of value in reducing phosphorus movement off farms. Other practices that limit phosphorus showing up at higher levels in tile drains also include using no-till and subsurface placement of fertilizer versus surface broadcasting.

Kevin McKague, an engineer with the Ontario Ministry of Agriculture Food and Rural Affairs, is also doing research on McIntosh’s farm, monitoring the water coming from the edge of the farm fields. McIntosh’s farm is an exceptional place to do such research as a berm was created 30 years ago to manage surface runoff from 52 acres. The water is held by the berm and then it flows off through a Hickenbottom drain. The berm overflows a couple of times per year, says McIntosh and that flow is managed along a grassed waterway and through culverts near the house out to roadside ditches.

Farm field edges are where nutrients leave and run into the rest of the environment, so it is important to know what levels are being moved off of the fields.

Once the equipment is installed, McKague says they can work with the landowner to try different production practices on the fields and assess their nutrient movement impact.

Kevin McKague. photo: John Greig

“They could plant a cover crop and see if it results in less soil loss or in reduced phosphorus loads,” he says, adding that the challenge of doing research in real-world situations is that the rainfall events needed to create measurable outcomes doesn’t always happen.

“You may not get the rains that can generate the runoff in the first place.”

McKague is looking at the difference between what flows off the field on the surface and what leaves the field via tile drainage.

“We find a good percentage of water leaving the field, in the ones we monitor, maybe 60 to 80 per cent leaves through the tile drains. The other 20 to 40 is overland,” he says. “The other factor is the quality of the water that is leaving.”

Water leaving over the land has a much higher concentration of sediments, compared to tile drains. When you look at loads to the Great Lakes, that means that the impact is split about 50-50 between tile and overland flow. That also means that mitigating overland flow will have a higher immediate impact on the amount of nutrients reaching the Great Lakes.

About the author

Field editor

John Greig

John Greig is a field editor for Glacier FarmMedia.

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