Tile drainage: What you see and can't see
Wisconsin Dells — Minnesota and Wisconsin Discovery Farms programs have monitored tile drainage on 14 different sites with a total of 47 site years of data. This on-farm data offers valuable information on when and why losses happen from tile drainage.
During the recent Discovery Farms conference in Wisconsin Dells Tim Radatz, head of the Minnesota Discovery Farm Program, highlighted what the data says about mechanisms for loss and how much is being lost and when.
In the Minnesota and Wisconsin tile study, the researchers found tiles flow 195 days a year while surface water only runs off about 10 days a year.
There are also differences between the timing and intensity of surface runoff and tile flow.
Tile flow is relatively consistent throughout the year, whereas surface runoff is often inconsistent. Tile drainage has many more days of flow and generally occurs at a different time of year than surface runoff.
“Soil and phosphorus losses are typically five times higher from the surface compared to the tile," Radatz said. "Most often, soil and phosphorus loss is controlled by adopting management strategies that reduce erosion.”
He added that there are certain cases when soil and phosphorus losses are higher from tile sites than from surface sites. These scenarios suggest that updating and maintaining the tile systems and managing soil test phosphorus levels can help prevent such high losses.
Nitrogen losses are typically five times higher from tile lines compared to surface. Nitrogen loss is controlled by adopting management strategies that reduce leaching into tile systems. On average, for every inch of tile flow, 5 pounds per acre of nitrogen is lost. Nitrogen losses can be reduced by decreasing the amount of tile flow or the concentration of nitrogen.
Radatz suggested three basic steps for prevention of nutrient loss through tile systems.
First, he pointed out that where problems occurred, they were generally in the older tiling systems of concrete or clay tiles that had blown out or plugged. Sites with corrugated plastic had almost no soil loss compared to sites with concrete or clay. Also, particulate phosphorus concentrations increased as soil concentrations decreased.
Gaps in connections of concrete and clay pipes are larger than the perforations in modern corrugated plastic tile and allow more soil particles to pass through.
He also pointed out that surface intakes allow more soil to enter the system because they are directly connected to the surface.
Collapses can create direct conduits to the soil surface. Radatz suggested checking for degradation over time, inadequate venting, outlet blockages and animal burrows. Also, adequately size mains and use proper joints to prevent collapse.
The Discovery Farm study found that dissolved phosphorus concentrations increased as soil test phosphorus levels increased. Routine soil testing and following recommendations for fertilizer will effectively manage soil test phosphorus levels and reduce dissolved phosphorus levels.
Finally, Radatz suggested considering timing and rate of nutrient application to reduce nutrient loss.
“Applying the proper rate of nitrogen is essential to reduce nitrogen losses through tile systems," he said. "Many studies show that nitrate concentrations in tile flow decrease as nitrogen fertilizer rates decrease.”
The timing of the application also has a large impact on water quality. Switching nitrogen applications from fall to spring has the most potential to limit losses because the time between application and crop uptake is decreased.
If still applying in fall, he suggested waiting until soil temperatures are below 50 degrees, or use a nitrification inhibitor to reduce the potential for losses.