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Wood Chips Could Help Cleanse Farm Field Run-Off


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By strategically placing organic matter to stanchion the water flow between farmers’ fields and nearby ditches and streams, he hopes to trigger a natural chemical reaction in which bacteria capture nitrogen in the run-off and help transform it into less dangerous gaseous forms.

According to Walter, associate professor of biological and environmental engineering, the drainage systems that help salvage wet fields can also help ferry pollutants into our water supply. “Tile drains” – which are actually perforated pipes – quickly whisk water away from fields before it has a chance to soak through landscape and benefit from natural “filtration” processes. This can lead to elevated levels of nitrogen, phosphorous and other nutrients found in fertilizer that feed algal blooms and rob waterways of oxygen needed to support fish and other life forms.

“It’s a big problem in New York. It’s a big problem everywhere. We are a little desperate to find some way to get rid of nitrates,” Walter said.

His solution is to dig large square trenches that are then filled with wood chips and buried. The field drains would flow into these “bioreactors.” The decomposition of the wood chips would release carbon that feed bacteria. The bacteria, in turn, would use nitrate from the run-off water as part of their respiration process, converting it to nitrate gas.

Some of the trenches will also contain biochar, a charcoal-like material created from the carbonization of biomass, which has been shown to help absorb phosphorous and pesticides in soil. Finding natural ways to control that pollutant as well would be a valuable added bonus, Walter said.

Early proof-of-concept experiments at the Homer C. Thompson Vegetable Research Farm in Freeville, N.Y. – funded in part by $90,000 of Cornell University Agricultural Experiment Station U.S. Department of Agriculture (USDA) Hatch funds – showed promising results, enough to prompt the USDA to award Walter and his colleagues – Steenhuis, professor of biological and environmental engineering, and Geohring, senior extension associate – an additional $530,000 to do further studies at a larger scale.

They will work with four or five farms in Upper Susquehanna, in the Chesapeake Bay watershed, where an estimated 300 million pounds of polluting nitrogen has led to poor water quality and a spot on the Environmental Protection Agency’s “dirty waters” list.

Similar techniques have been tested in the Midwest; in Iowa, environmental incentives have been set up to help defray the costs of installation, which range from $7,000 to $10,000 to treat drainage from 30 to 100 acres.

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