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Treating Nitrates

Over-Applying Farm Chemicals Can Lead to Water Quality Issues
The Gulf of Mexico's "Dead Zone" is largely attributed to agricultural runoff from the Midwest. Agriculture has been similarly targeted closer to home, where amounts of nitrogen in Iowa's drinking water supplies have increased dramatically throughout the past century. For example, in a 2000 U.S. Geological Survey study, average annual nitrate concentrations in the Des Moines and Cedar Rivers have increased nearly seven times over the last 100 years, from about 0.6 milligrams per liter to as much as 4.6 mg/l. And data provided by Des Moines Water Works dating back to the 1930s shows nitrate levels in the Raccoon River stayed consistently below 1 mg/l until the mid 1960s. Since then, nitrate levels have increased to as high as 10.2 mg/l in 2002. Over the last 20 years, average nitrate levels in the Raccoon River average 7.3 mg/l.

What Can Be Done

  • Reduce inputs. The best way to prevent nitrates and other chemicals from leaving crop fields, either through runoff or leaching into groundwater, is to simply reduce the amount of fertilizer and pesticides that are applied.
  • Improve soil health. Healthy soils have deeper topsoil layers which are high in organic matter. This organic matter layer allows soils to hold water and nutrients like a sponge until plants need them. Ways to improve soil health include reducing or eliminate soil disturbing activities, such as tillage, and adding diversity to a crop rotation, with practices like cover crops.
  • Implement a Drainage Water Management (DWM) system. DWM systems allow farmers to manage drainage tile water levels with a water control structure, much like those used to control wetland water levels. Water level structures are simply retrofit to an existing tile system.

Additional Resources

Conservation Practice Standards
Job Sheets
Websites/Conservation Programs

Christian Osborn, State Engineer
Phone: 515-284-4357