For a number of farms in the Midwest, nitrapyrin is used to help hold nutrients in agricultural fields until the plants have a chance to use them. Nitrapyrin increases the availability of nitrogen fertilizer, which boosts crop production. Therefore, nitrapyrin can improve nitrogen use efficiency, reduce nutrient losses, and thereby mitigate eutrophication (excess nutrients spurring exponential growth of algae in lakes).
Nitrapyrin and other nitrogen inhibitors work by limiting the conversion of ammonium to nitrite (first step of nitrification). Nitrapyrin also restricts the formation of nitrate from nitrite (second step of nitrification). Nitrate is one of the major contributors to eutrophication.
While the use of nitrapyrin has benefits, concerns have been raised about whether its runoff from fields into nearby rivers and streams could have an impact on bacteria and the nitrification process in those water bodies. Even though nitrapyrin has been used as nitrification inhibitor and soil bactericide since the early 1970s, there is limited information on its fate and transport from fields into aquatic ecosystems.
As an initial step to quantify the amounts of nitrapyrin present in fields and streams, ISTC researchers Wei Zheng and Nancy Holm collaborated with scientists from the U.S. Geological Survey (USGS) to undertake a one-year study of its occurrence in seven streams and nearby farm fields in Iowa and Illinois. The team examined the concentrations of nitrapyrin, its metabolities, and three widely used herbicides – acetochlor, atrazine, and metolachlor – in soil and water samples.
Results from their recently published article showed that nitrapyrin was found in many of the samples. It was sorbed to soil particles, transported from fields via overland flow, and leached into subsurface drains. In addition, all three herbicides were found in the stream samples with atrazine being the most concentrated of the three, especially at peak application times.
This research project extends the previously published pilot study on nitrapyrin by the USGS and is the first to show the transport of nitrapyrin from fields to streams over an entire year. In addition, this study is the first to describe nitrapyrin transport via subsurface drains, although those concentrations were much lower than surface concentrations. Studies such as this can help provide decision makers with a better understanding of the fate of chemicals applied to agroecosystems.