Excessive Nitrogen Application Depleting Soil Carbon Pools

University of Illinois researchers find N fertilizer may be 'browning the green revolution' by reducing soil carbon and nitrogen levels

Apr. 18, 2026 at 5:26am

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A bold, highly structured abstract painting in earthy tones of brown, green, and blue, resembling a massive scientific diagram with sweeping geometric arcs, concentric circles, and precise botanical spirals, conveying the delicate balance of the soil ecosystem.This abstract illustration conceptually represents the complex interplay between soil carbon, nitrogen, and synthetic fertilizer application, as revealed by the University of Illinois research.Ellsworth Today

According to University of Illinois fertility specialist Richard Mulvaney and fellow researchers Saeed Khan and Tim Ellsworth, excessive nitrogen (N) fertilizer application is depleting soil carbon and nitrogen levels across decades-long farm plots in the U.S. and Europe. Their data contradicts the common belief that N fertilizer helps build organic matter, as they found losses in soil carbon and N over time in fields fertilized with N-P-K as well as unfertilized control plots.

Why it matters

This research challenges the long-held assumption that N fertilizer is critical for increasing crop yields and building soil organic matter. If Mulvaney's findings are accurate, it could have significant implications for sustainable farming practices and the role of synthetic fertilizers in modern agriculture.

The details

Mulvaney and his team analyzed data from decades-long farm plots across the U.S. and Europe and found that regardless of whether the fields were fertilized with N-P-K or left unfertilized, there was a loss of soil carbon and nitrogen over time. This contradicts the common belief that N fertilizer helps build organic matter. Mulvaney argues that the continued increase in corn yields in Illinois since the 1980s, when N application rates leveled off, suggests there is another source of nitrogen beyond synthetic fertilizers - the soil itself.

  • Mulvaney and his team have been analyzing the data for several years.
  • Corn yields in Illinois have improved from around 60 bushels in 1960 to nearly 180 bushels as of 2010.

The players

Richard Mulvaney

A fertility specialist at the University of Illinois who led the research on the impacts of excessive nitrogen fertilizer application.

Saeed Khan

A researcher who collaborated with Mulvaney on the study.

Tim Ellsworth

A researcher who collaborated with Mulvaney on the study.

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What they’re saying

“There is another source, and it's a four-letter word called 'soil.'”

— Richard Mulvaney, University of Illinois fertility specialist

The takeaway

This research challenges long-held assumptions about the role of nitrogen fertilizers in modern agriculture, suggesting that excessive application may actually be depleting soil carbon and nitrogen levels over time. The findings could prompt a re-evaluation of sustainable farming practices and the reliance on synthetic fertilizers to boost crop yields.