Bioreactor to Reduce Nutrient Loss

Patrick Kirchhofer - Peoria County Farm Bureau

On July 21, 2017, the first bioreactor in Peoria County was installed on a farm owned by Mike Windish, about one mile south and a half mile west of the Route 116/Taylor Road intersection.

A bioreactor is one way to remove nitrates from water draining out of tile lines, which can be found in farm fields across central Illinois, especially those that are flat or have very little slope to them. This flexible black tubing, about four to six inches in diameter, is placed in fields approximately three feet deep, with around 40 feet between each line. They are then connected to larger tile lines, eight to 10 inches in diameter, in the field. The tile is perforated, which allows water to drain into it as it percolates through the soil profile. The water from the large main tile eventually drains into a ditch, waterway or small stream.

Tile has been installed in Illinois farm fields for decades. Farmers can often find old tile made out of clay, which was placed in fields in the early to mid-1900s. Some of it may still be functional, but most of the clay tubing has collapsed over time, impeding water drainage.

Tile is the primary reason we are able to grow crops in our state’s rich, dark soil. Excessive rain and the pooling of water on the surface of fields will drown both corn and soybean plants if they are submerged for three or more days. Standing water in fields also causes nitrogen that was applied to the field to be lost through a process called denitrification. From a broader view, tile lines may also reduce soil erosion as water slowly drains from the soil, which allows more rainfall to soak in instead of running off the surface, carrying loosely tilled soil with it.

The loss of nitrates, fertilizers and soil from farm fields is both a short- and long-term loss to farmers and landowners. Nutrient loss decreases the available fertilizer for growing crops, while soil loss decreases the potential yield and value of the land. In addition, there is concern downstream with water, nutrient and soil runoff from farm fields. Nitrates and other nutrients in water, for example, can cause algae blooms. As dead algae decomposes, oxygen is consumed, resulting in low levels of oxygen in the water. The Gulf of Mexico Hypoxia Zone is a large area at the mouth of the Mississippi River and along the Louisiana and Texas coasts where this phenomenon occurs each summer. Nitrates, phosphorus and soil loss are partially blamed for the cause.

The Illinois Nutrient Loss Reduction Strategy was developed in response to the U.S. Environmental Protection Agency’s 2008 Gulf Hypoxia Action Plan, which calls for each of the 12 states in the Mississippi River Basin to develop a plan to reduce the amount of phosphorous and nitrogen carried in Illinois waterways and eventually to the Gulf of Mexico. In 2011, the EPA provided a recommended framework for state plans. Illinois' strategy, which follows this framework, will play a critical role in reducing nutrients, since we are one of the largest crop-producing states in the country.

As mentioned earlier, bioreactors are one way to reduce nitrate loss from farm fields. The area being drained at the bioreactor site in Peoria County covers 200 acres. Tile water from 80 acres of this field is being drained into the new bioreactor, while the remainder of the acreage carries excess water off the field by grass waterways.

So what exactly is a bioreactor? A soil pit is dug where the main tile line drains from the field; the bottom is lined with a plastic sheet and filled with about four feet of wood chips. On top of the woodchips is a geotextile fabric, then a layer of soil three feet deep. As the water from the tile line drains into the pit, the woodchips contain microbes which convert the nitrates to a nitrogen gas, which is safely released into the air and essentially removed from the water.

Cover crops, no-till farming, buffer strips along stream borders, saturated buffers, dry dams, terraces and split applications of nitrogen are other conservation options for reducing the nutrient and siltation load in water runoff. Although bioreactors are not a cure-all for nitrates leaving farm fields, much is being learned from this new concept. It is another tool in the toolbox farmers can use to be good stewards of the land and take care of our environment. iBi

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