Edge of Field Practices

Oct 31, 2023

Conservation on the Edge
Evan Brehm
Iowa Soybean Association
                Buried a few feet under thousands of acres of row crops lie black plastic drainage tubes known as tile. Tile is an expensive yet necessary implementation to grow row crops in Iowa. It can be debated as being the greatest return on investment a landowner can have. The tile line underground takes water from rainfall events and diverts them to an outlet source that is often a creek or a stream. Along with water leaving a field can come nutrient runoff.

 Nutrient runoff can be managed using nutrient stabilizers, variable rate technology for fertilizers, split applications of nitrogen, tillage reduction, cover crops, or a combination of any of these. A perennial system that can be seen on the edge of fields and near streams are called filter strips or buffer strips. These strips can be anywhere from 30 feet wide to much bigger. These strips consist of a perennial grass that sequesters nutrient runoff from fields. Within these strips are tile lines carrying water that could contain nutrients such as nitrates or phosphates, often associated with row crop agriculture.

                The edge of the field is an important place. With hundreds of feet of tile line buried below, wildlife and pollinators take advantage above ground. Come November and December it’s hard not to see a buffer or filter strip scattered with blaze orange and German Shorthairs tracking down the prized ring-necked pheasant. Pollinators and beneficial insects move in here during the growing season that can assist with predatory insect species on row crops.
                Over the past decade, Edge of Field (EOF) practices have drastically increased. These include: denitrifying bioreactors, saturated buffers, and wetlands. EOF practices can be installed in an existing perennial buffer and tied into existing tile lines. Depending on the EOF practice, nutrient runoff can be reduced anywhere from 40-90%. This meets the goals of the Iowa Nutrient Reduction strategy. If you own land in the Middle or Lower Cedar watershed, these can be paid in full with additional easement incentives. 100% PAID, no cost. These practices improve water quality downstream that is good for people, agriculture, and the environment.

Image Courtesy Farm Journal Magazine Denitrifying bioreactor: tile line is routed through a wood chip basin, typically 3-4 feet deep. Size after that depends on the amount of acres that are being drained. Woodchips are a high carbon source and when water enters, bacteria being to break down the nitrates before leaving through an outlet that goes into a stream.
Image courtesy of Farm Journal Magazine

A diagram of a field with a stream and a outletDescription automatically generated with medium confidenceSaturated buffer: tile drained water enters a lateral tile that is parallel to a current buffer strip.  The water moves across the length of the buffer strip which removes nitrates. Not only does this slow down water flow, it allows microbes to break down nutrient runoff prior to entering a water source. These need to be located with a tile outlet near a stream.
Image courtesy of USDA

Wetlands: shallow in depth and take time to engineer. Wetlands help reduce nutrient runoff, enhance wildlife, and can mitigate flooding. Areas to consider are unproductive acres that are wet year after year. Wetlands take longer to construct than the previous two EOF practices and cost more. Results can be seen year one. Samples were taken on a tile line coming into the wetland, and on the control structure leaving the wetland. See below results from a Linn County wetland. On average nitrates were reduced by 84.86%.


Water samples were performed in field and sent to the Iowa Soybean Association Water Lab in Ankeny. The accredited lab is certified by the U.S. Environmental Protection Agency (EPA) through the Iowa Department of Natural Resources to analyze E. coli bacteria, nitrates, nitrites and fluoride under the Safe Drinking Water Act.

If you are interested in any of these practices, get started today! There are opportunities to have these 100% funded for. On top of that, reducing nutrient runoff has many advantages. Counties within the Middle Cedar Watershed are continuing to do a “Batch and Build”. When several EOF practices are of interest, local experts will come for a site visit and determine the best location. It’s time to get on the edge of conservation. Let’s get an ‘Edge of Field’ practice installed today on your land. Please reach out to Evan Brehm or your sales agronomist.

Evan Brehm
Iowa Soybean Association


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