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Synthetic Nitrogen Lingers for Decades

Runoff_of_soil_&_fertilizerNitrogen fertilizer applied to crops lingers in the soil and leaks out as nitrate for decades towards groundwater — “much longer than previously thought,” scientists in France and at the University of Calgary say in a study.

Thirty years after synthetic nitrogen (N) fertilizer had been applied to crops in 1982, about 15 percent of the fertilizer N still remained in soil organic matter, the scientists found.

After three decades, approximately 10 percent of the fertilizer N had seeped through the soil towards the groundwater and will continue to leak in low amounts for at least another 50 years.

The findings show that losses of fertilizer N toward the groundwater occur at low rates but over many decades, says Bernhard Mayer, U of C professor of geochemistry and head of the Applied Geochemistry Group.

That means it could take longer than previously thought to reduce nitrate contamination in groundwater, including in aquifers that supply drinking water in North America and elsewhere, he says.

“There’s a lot of fertilizer nitrogen that has accumulated in agricultural soils over the last few decades which will continue to leak as nitrate towards groundwater,” Mayer says.

Canada and the United States regulate the amount of nitrate allowed in drinking water. In the 1980s, surveys by the U.S. Environmental Protection Agency and the U.S. Geological Survey showed that nitrate contamination had probably impacted more public and domestic water supply wells in the United States than any other contaminant.

The study, “Long-term fate of nitrate fertilizer in agricultural soils,” was published in the Proceedings of the National Academy of Sciences.

This summary appears in the December 2013 issue of Acres U.S.A.

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