Managing Denitrification in the Corn Belt With Bioreactors and Wetlands.

In the Corn Belt, reducing nitrate loads from tile-drained corn and soybean fields has been difficult. Few practices have received much adoption, and much hope has been placed on end of tile bioreactors and wetlands. In this poster, opportunities and limitations of both practices will be summarized. Wood chip bioreactors are easy to install, remove approximately 50% of the tile nitrate load, and take little land. However, costs are typically high and landowners will not install them without cost sharing for most of the installation costs. At high flow absolute nitrate removal rates are high (g N removed per m3 of bioreactor), but the % reduction is reduced. For wetlands, construction and land costs can be very high. There are important differences across the Midwest thought. In Iowa, large wetlands of 1-5 ha intercept tile mains draining 400-500 ha, and a 1% wetland/watershed area (as a percent of the watershed area) can remove 50% or more of the nitrate load. In Illinois and Indiana, constructed wetlands are typically at the end of a single field tile line of only 20 to 50 ha, and are smaller (< 1 ha) and need to have a wetland/watershed area of about 5% (taking more land). Is seems unlikely that programs could fund enough bioreactors and wetlands across the tile-drained Corn Belt to greatly reduce nitrate loads. These methods of nitrate reduction seem more applicable to high value sources of nitrate, such as greenhouses or vegetable crops, and suggest in-field methods of nitrate reduction may be easier to apply across the Corn Belt.