Gary Feyereisen, an agricultural engineer with the USDA-ARS, St. Paul, Minn., is evaluating the water quality effects of French drains in two quarter-section tiled fields in west-central Minnesota. The corn silage fields, which receive annual manure applications, had 48 open surface-tile inlets. All but two were replaced with birdseed sand French drains. “In the three years with the new intakes, average concentrations of sediment in the drainage water have gone down,” Freyereisen reports.

Another inlet alternative is intensive tiling of field potholes, says Gary Sands, University of Minnesota Extension agricultural engineer. Narrowly spaced tile pipes are installed in a shallow grid or coil in the middle of a wet spot. “In new tile systems, contractors have been putting a lot of these in.”

Sands says all these alternative inlets protect water quality better than open inlets, while still providing adequate drainage.

At the University of Illinois, graduate student Stephanie Herbstritt designs and tests filters that can be retrofitted to existing tile inlets or outlets. The goal is to keep out pollutants such as spilled anhydrous ammonia or phosphorus, without lowering drainage capacity.

“There is a need for these innovations,” she says. If regulations on drainage water quality tighten, as they are expected to do, “farmers will need economical solutions.”