Fate and Transport of Nitrapyrin in Agroecosystems

For a number of farms in the Midwest, nitrapyrin is used as a nitrification inhibitor and co-applied with nitrogen fertilizer to farm fields. The purpose of the inhibitor is to limit the first step of the nitrification, which is the conversion of ammonium to nitrite. The inhibitor also restricts the second step of the process – the formation of nitrate from nitrite. The result of nitrapyrin applications is more ammonium available for plant growth and less nitrate available to run off fields.

Nitrogen Cycle

Even though it has been used since the early 1970s, there is limited information on the fate and transport of nitrapyrin from fields into aquatic ecosystems. There have been concerns raised about whether nitrapyrin runoff from fields into nearby rivers and streams would have an impact on bacteria and the nitrification process in those water bodies. As an initial step to quantify the amounts of nitrapyrin present in fields and streams, ISTC researchers Wei Zheng and Nancy Holm teamed with scientists from the U.S. Geological Survey (Emily Woodward, Dana Koplin, Shannon Meppelink, Paul Terrio, and Michelle Hladik) to undertake a one-year study of nitrapyrin concentrations in seven streams and nearby farm fields across Iowa and Illinois. The team analyzed the occurrence of nitrapyrin, its metabolities, and three widely used herbicides – acetochlor, atrazine, and metolachlor – in soil and water samples.

Results from the study showed that nitrapyrin was found in many of the samples. It was sorbed to soil particles or was transported off fields via overland flow and leaching to 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 study extends the previously published pilot project on nitrapyrin by Woodward et al. (2016). This study is the first to show the transport of nitrapyrin from the fields to streams over an entire year. It is also the first to describe nitrapyrin transport via subsurface drains, though those concentrations were much lower than surface concentrations.