Tile drainage shows potential, but requires more research

Controlling runoff | Manitoba’s Red River Valley and hog producers create unique challenges

Huge amounts of tile drainage are being installed throughout Manitoba’s Red River’s basin, but little is known about how it affects nutrient runoff.

However, a leading soil scientist specializing in prairie water problems thinks the drainage systems are probably a good thing.

“If you look at runoff coming through tile lines versus if that water had run off the surface, if it runs off the surface it’s going to be carrying a lot more nutrients than if it’s going through the tile line,” said David Lobb of the University of Manitoba in an interview during the Keeping Water On The Land conference in Winnipeg June 17.

However, Lobb said there’s little research on Red River Valley and prairie tile drainage situations and most research relied upon comes from Ohio and Ontario.

Nutrient runoff is a major issue in Manitoba, with farmers vulnerable to government regulation due to perceptions of agricultural runoff causing the nutrification that some say could kill Lake Winnipeg.

For years nitrogen was targeted as a probable problem and farmers modified practices to minimize losses. But in recent years, phosphorus has been identified as a bigger problem.

Controlling phosphorus has been hard in some areas, especially those with large numbers of pigs.

High phosphorus output in pig manure has crimped hog production in parts of the Red River Valley where farmers can’t find enough land to spread all the manure their barns produce, at least not at rates required by Manitoba regulations.

But most of the agriculturally based phosphorus outflow comes from water pouring off the surface of fields, many scientists say.

Water from snow melt and rain absorbs phosphorus from the land and then pours into drains, which lead to Lake Winnipeg.

Controlling that surface runoff might be key to reducing nutrification, and tile drainage might help do that, Lobb said.

Much phosphorus is probably locked in the soil as water trickles down into tile lines, so that would be better than draining the water off the surface.

And tile drainage could slow the flow of the water, reducing it from the rush off the surface of the soil that is prevalent today.

Most Red River Valley fields have surface drainage lines so little water remains on the field soon after rain or spring melting.

Lobb said research from Ontario and Ohio is useful, but those areas have different land and farming situations.

In Ontario a lot of water sits stranded in fields, but tile drainage helps get it off the land quickly. In Ohio, the land traps much water too.

But in the Red River Valley, the water is already moving off the land quickly, so tile drainage is used mainly to change how it flows to drainage channels.

Tile drainage is just beginning to appear in Manitoba, but is already widespread in eastern North Dakota.

That makes it important to research the positives and negatives now, Lobb said.

As well, he said that doesn’t mean research in the Red River Valley necessarily applies to the entire Prairies.

Tile drainage that partially replaces surface drainage is different from using tile drainage to drain potholes of stranded water in areas where those are common.

“We don’t know enough about either of these two to know the full impact, the full range of affects of either of these on water quality and quantity,” said Lobb.

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