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Nitrogen Fertilizer’s Long-Lasting Legacy

Aerial of intersecting roads in rural IndianaDangerous nitrate levels in drinking water could persist for decades, increasing the risk for blue baby syndrome and other serious health concerns, according to a new study published by researchers at the University of Waterloo. Nitrogen fertilizer applied to farmers’ fields has been contaminating rivers and lakes and leaching into drinking water wells for more than 80 years. The study, published in the journal Environmental Research Letters, reveals that elevated nitrate concentrations in rivers and lakes will remain high for decades, even if farmers stop applying nitrogen fertilizers today. The researchers have discovered that nitrogen is building up in soils, creating a long-term source of nitrate pollution in ground and surface waters. “A large portion of the nitrogen applied as fertilizer has remained unaccounted for over the last decades,” said Nandita Basu, a professor in the Department of Earth and Environmental Sciences and Civil and Environmental Engineering. “The fact that nitrogen is being stored in the soil means it can still be a source of elevated nitrate levels long after fertilizers are no longer being applied.” Their paper presents the first direct evidence of a large-scale nitrogen legacy across the Mississippi River Basin. Professor Basu and her group analyzed long-term data from over 2,000 soil samples throughout the Mississippi River Basin to reveal a systematic accumulation of nitrogen in agricultural soils. In many areas this accumulation was not apparent in the upper plow layer, but instead was found 25-100 centimeters beneath the soil surface.

This article appears in the May 2016 issue of Acres U.S.A.

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