Lake Winnipeg might be drowning in phosphorus, but plenty of soils in the province are gasping for it.
Lake Winnipeg has become infamous for its water quality, and not in a good way. Algal blooms and E. coli cases have become a familiar state of affairs in the south basin, while over half of samples collected as part of a Canadian Environmental Sustainability Indicator in 2013 fell short of the standards on phosphorus.
Victoria Beach bore the brunt of that again this year when toxic blue-green algae coated the shore, something that has become all too common for cottagers.
Why it matters: Manitobans are fighting an uphill battle against phosphorus levels in Lake Winnipeg, but modern, systematic, long-term fertilizer management might help bridge the gap.
The issue has led to endless debates, non-profits dedicated to improving water quality, legislation that curbed hog barn development for years and three rounds of national inquiries, all in the hope of reversing — or at least slowing — the problem.
“There are multiple sources of phosphorus and multiple factors that impact phosphorus loss from fields and there have been multiple calls for research to start to better understand that so we can better manage our agricultural resources,” Lake Winnipeg Foundation executive director Alexis Kanu said.
The foundation currently runs a citizen water sampling network to monitor water quality flowing into the lake and tag phosphorus hot spots.
Lake Winnipeg’s unique traits, however, make it hard to fully understand. Its catchment area spans from the Rocky Mountains to northern Ontario and south through the Red River well into the United States. In total, four provinces and four states contribute to the lake, areas largely rich in agriculture with the same agricultural need for phosphorus fertilizer.
The shallow lake has been collecting those nutrients for decades, nutrients now sitting at the bottom of the lake and continuing to contribute to the overall load. The 2018 Lake Winnipeg Basin Initiative report noted that internal phosphorus loading contributed at least as much phosphorus as the rivers flowing in. The top seven centimetres of lakebed is expected to play into nutrient loading for decades yet.
For farmers though, phosphorus comes with an opposite set of management problems. Many fields don’t have enough of it.
A study done every five years by Manitoba Agriculture showed that well over half of Manitoba’s soils, 57 per cent, were “critically” short of phosphorus in 2010, numbers that jumped to 64 per cent five years later.
It’s something that John Heard, a crop nutrition specialist often tapped to speak on soil health and soil conservation, has noted with concern.
“There’s no public trust or advantage to society to keep soils depleted into a non-productive state,” Heard said. “The public trust comes with knowing that they’re using some science-based philosophy and due diligence to come up with their phosphorus management and most of it is not to do with the rates.”
Heard says it’s the placement and the timing that are key. Farmers place the nutrient under the soil surface, primarily in a band, which helps keep the nutrient where it’s needed for the growing crop.
“If people are sitting around thinking that farmers have to change the things that they do or the way that they’re thinking, they better plan to sit for a long time, because farmers are already doing those things,” Heard said. “Right now, that’s the thing that’s frustrating the farmers because the traditional practice of managing phosphorus is very well within the environmental framework.”
Heard pointed to current regulations that, among other things, forbid manure spreading between Nov. 10 and April 10.
Those short soil levels become even more critical given Manitoba’s cold springs and short growing season, University of Manitoba soil fertility researcher Don Flaten said.
“When the soil is very cold, it doesn’t provide phosphorus very well and also the plants’ root growth, our crops’ roots, are growing very slowly and not functioning very well at taking up phosphorus,” he said. “Our crops have a more dire need for supplemental phosphorus in early spring than a crop that is growing in a warmer soil. In an area where they have a longer growing season, they’re not as concerned with maturing that crop quickly.”
Best of both worlds
The divergence between water and soil pose a unique problem to Manitoba. Agronomically, there is little doubt that producers need to be able to apply phosphorus, and in levels to match the larger yields being taken off the field. At the same time, there is public pressure to curb nutrient run-off linked to the quality issues in Lake Winnipeg.
There is no real need for those goals to be at odds, according to both Flaten and Heard.
In particular, the industry’s embrace of the 4R philosophy (applying the right type of fertilizer at the right time, at the right rate and in the right place), has drastically reduced potential nutrient run-off while promising less phosphorus loss to the crop, both say.
Heard urged farmers to test soils and get a baseline inventory on their phosphorus to base their plan on.
Manitoba Agriculture is now urging producers to look even further than the 4Rs. This summer’s Crop Diagnostic School in Carman pitched a more complex decision-making model that asks the farmer to consider their equipment, economic reality, whether the land is rented or how close they might be to retirement, since a producer may see little incentive to build up phosphorus in the soil, just to leave the business and have someone else benefit.
“Historically, we only had recommendations that we would refer to now as short-term sufficiency, so an approach that the rates are fairly low or conservative, but they provide really good economic return in that year,” Heard said. “But what we’ve come to recognize is that those rates have not kept pace with the yields people are getting and that’s been one of the contributors to soils becoming depleted.”
The new way of thinking eliminates blanket recommended rates, and instead targets a “good working range,” of 10 to 20 parts per million, according to Heard. Farmers testing below that range should gear their program to building phosphorus by applying more than a crop needs, although still with the 4R principles. Many farmers may already be in that range and will only need to match phosphorus with crop removal, Heard noted.
Rotations will also play a critical role as farmers merge longer-term strategy with higher-yielding crops, Flaten said. Soybean and canola may now remove more phosphorus than can be safely applied with the seed at planting. The farmer can avoid those concerns, however, by shifting some of that extra phosphorus to a wheat year, since the cereal is less prone to toxicity, experts say. The strategy was pitched during a canola seminar in Dauphin last year.
In 2012, a paper by then Brandon AAFC researcher Cynthia Grant also suggested side banding as a less toxic option to seed-placed fertilizer.
Others are turning to side banding phosphorus along with nitrogen in the fall, Heard said, although some agronomists are wary about losses with fall-banded nitrogen. Phosphorus, as the less mobile nutrient in the soil, causes fewer of those concerns.
“I think what we’re really trying to stress is that phosphorus management is not a short answer,” Heard said. “It’s a conversation that agronomists need to have with the farmer, based on their strategy and their equipment and then they can figure out what would be an appropriate rate that fits their cropping system and their equipment.”