Based on the number of interactions and the range of questions and comments relating to water issues and agriculture I’ve had, I would conclude that tile drainage is the most misunderstood practice employed on Minnesota farms.
Ongoing debates about agricultural drainage and water quality are often fueled by a mixture of incomplete or partial truths — and very inaccurate information. I’ll make the same disclaimer here: that given the complexity of the topic, readers will likely point toward specific examples outside the general parameters listed as I attempt to shed some light on some of the most common misperceptions about tile drainage.
Here are five myths about farm tiling:
1. Tiling is totally unregulated. Tiling is one of the most highly regulated activities affecting farmers. Several federal, state and local agencies have regulatory authority under various federal, state and local laws, rules and ordinances allowing review of drainage projects. Some drainage activities require permits, while others are simply reviewed and either approved or denied. It is common for as many as seven regulators to review a proposed drainage project to insure compliance with all rules.
2. Tiling speeds water movement off the land. Compared to surface runoff, tiling moves water quite slowly. The maximum capacity of tile systems is in the range of a half-inch of drainage per day. Concerns about swollen ditches and streams are legitimate, but as I look at data collected over the last century, the underground tile portion of drainage systems is a very small contributor during high flow periods. Keep in mind that streams and ditches carry both tile water and surface runoff, and that high flows generally occur over relatively short periods of time — right after larger rains that cause significant overland surface runoff. Many older tile systems also convey surface runoff that gathers in low spots with open inlets. Modern tiling practices usually result in systems with fewer open inlets.
3. Tiling contributes to water quality problems. This is an issue of trade-offs. Tile water does contain nutrients and sediment. There is a large body of research showing that tile drainage reduces surface runoff, resulting in less sediment transport. There is a corresponding reduction in phosphorus losses, though not quite as large due to the presence of a very small amount of dissolved phosphorus contained in tile water.
Tile drainage also contains nitrates. The key to determining the net effect of tiling lies in understanding how much sediment and phosphorus are reduced relative to the increase in nitrates. In my experience, in most situations the tradeoff is positive, especially considering that people need to eat, and farmers are becoming increasingly aware of this concern and are working ever harder at improving their nitrogen application practices. Solutions beyond the field are also happening, such as denitrification in wetlands and drainage ditches.
4. Tiling is not a conservation practice. Tiling is a conservation practice and a key to successful implementation of many other conservation practices. Consider that conservation can simply mean that land is left undisturbed as habitat, which meets some environmental goals — but, again, people need to eat. Once the decision is made to farm a tract of land, farming it with efficiency results in fewer acres required for crop production and more acres available for other uses, including habitat.
The technology available today allows drainage to be accomplished with less environmental impact and greater improvements in productivity than was possible 50 to 100 years ago. Well-designed tile systems that follow field contours and provide uniform drainage are the norm today. This allows more options for farmers to move to reduced tillage systems, improves nutrient uptake and extends the growing season in a region where days are at a premium.
5. Tiling is bad for soil health. Healthy soils contain both water and oxygen. Many of the most productive soils in the Midwest are not able to drain naturally, starving the microorganisms in the soil of oxygen. This, in turn, affects nutrient cycling in the soil and can reduce crop productivity, which is important in returning organic matter to the soil to continue the cycle. Improved drainage contributes to improved soil health.
As farmers respond to the challenge to reduce their impact on water, all farming practices come under scrutiny. I hope that a better understanding of the science behind tile drainage leads to a more productive discussion about beneficial drainage practices and promotes their application across more of the landscape.
Formo is executive director of the Minnesota Agricultural Water Resource Center.