Iowa State University's Mike Castellano discusses the factors driving nitrate levels in 2025 and how farmers are collaborating to improve outcomes.

Editor's note: The Spokesman recently sat down with Mike Castellano, Iowa State University (ISU) soil science professor and lead on the Iowa Nitrogen Initiative, to talk about water quality and ISU's efforts to help farmers optimize nitrogen application rates. Following are excerpts from that conversation. Answers have been edited for length. 

Why do we hear about high nitrate levels in water some years — like we are in 2025 — and not in others?

Castellano: We grow crops for nine months of the year. We have several months when there's no plant demand for nitrogen, and if we don't have plant demand for nitrogen, it's susceptible to loss to the environment. 

Wet weather obviously exacerbates that. So when we have no crop demand, if we don't have excess precipitation, we lose very little to the environment, as we saw in the past few (drought) years with relatively little nitrate loss and relatively low nitrate concentrations in the...