Tile drains are not nearly as effective at rapidly removing
excess water as people assume, a good thing if you
are concerned about applied animal nutrients getting into
surface water bodies.
Experiments conducted last fall on a farm in the Upper
Thames River watershed near Kintore were designed to
mimic the worst conditions for applying pig manure – wet,
macroporous soil in fields that are systematically tiled. The research team found that tile drain discharge, even under
those conditions, could only directly account for 10 to 15 per cent
of the water that was applied to the surface of the field.
“The bottom line,” Rudolph says, “is that tile drains capture
much less than we ever would have expected. It has
been conventionally assumed that the tiles have a very large
area of influence. Field experiments show the influence is
much smaller than we’d anticipate.”
“To help us further understand the risks that tile drains
impose on our water resources,” says Rudolph, “more field
experiments are being conducted in other geological settings
and under a wider range of climate conditions.” He also
adds that movement of the chemical tracers applied last fall
is still being monitored.