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Holistic Approach To Phosphorus Management Urged

“It’s time to treat environmental health like we do human health.”


They’re the latest buzzword in environmental management – beneficial management practices, or BMPs for short. Follow them and your farm will be environmentally sound, producers are told.

It sounds good in theory. But are BMPs really the answer to environmental problems on the farm?

Don Flaten has a cautionary note. Yes, BMPs are important. But they’re not a cure-all. And it’s a mistake to treat them as if they were.

Take phosphorus, a subject on which Flaten, a University of Manitoba soil scientist, has studied extensively.

Phosphorus is a unique element essential for all life forms. It can also be dangerous. Even small amounts of excess phosphorus can cause huge problems with water quality. Those include: blue-green algae blooms, oxygen depletion causing fish kills, and nerve and liver toxins which can endanger livestock and wildlife.

Reducing phosphorus in water run-off from the land is critical to improving the health of Lake Winnipeg, where algal blooms proliferate in summer, the Manitoba government stresses.

That’s why BMPs listed by Manitoba Agriculture, Food and Rural Initiatives in an environmental farm plan catalogue focus largely on reducing phosphorus run-off.

But are those BMPs effective in achieving their aims? Not necessarily, according to Flaten.

In a presentation last week at the annual Prairie Conservation and Endangered Species Conference in Winnipeg, Flaten described how BMPs aimed at controlling phosphorus run-off don’t always work as expected.

Flaten noted that 80 per cent of the run-off on the Prairies occurs during snowmelt. Most BMPs are geared to control phosphorus loss from run-off resulting from rainfall. Those include: conservation tillage, vegetated buffer strips, cover crops, perennial forages and wetland restoration.

But those BMPs don’t necessarily reduce phosphorus loss, Flaten told his audience as he went through them one by one.

That’s because many BMPs concentrate on retaining vegetation on the soil surface. Vegetative residues, when frozen and then thawed, may release large quantities of water-soluble phosphorus, Flaten said.

For example, studies conducted at South Tobacco Creek in south-central Manitoba found that conservation tillage, while reducing run-off and erosion, actually increased the loss of dissolved phosphorus.

Another 2006 study in southeastern Manitoba found vegetated buffer strips reduced total phosphorus run-off by only four per cent over all.

Perennial forages released more soluble phosphorus than they retained, as did native rangeland, according to other studies.

Restoring wetlands can also increase phosphorus loss, especially if phosphorus-rich topsoil on former agricultural land is not removed.

One BMP that does reduce phosphorus loading is fencing riparian areas to restrict cattle access to streams. However, it increases the number of parasites in the water because the cattle no longer chase away muskrats, which are big parasite carriers.

Such undesirable side-effects show BMPs aren’t necessarily a panacea for reducing phosphorus loss, said Flaten.

Later, Flaten stressed he wasn’t trying to discourage farmers from using BMPs. But he did recommend landowners apply them more carefully.

“It’s time to take a broader look at environmental issues and treat environmental health like we do human health,” said Flaten.

That involves diagnosing environmental cases individually, prescribing appropriate treatment and considering possible side-effects, rather than tackling them with one-size-fits-all BMPs, he said. [email protected]

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