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Nitrogen Fertilizer Leaches into Groundwater for Decades

Nitrogen fertilizer, used extensively in agriculture to enhance crop growth, lingers in soil and leaches into groundwater resources as nitrate for 'much longer than previously thought', according to a new research study conducted by scientists in France and at the University of Calgary. This not only results in eutrophication of freshwater and coastal ecosystems, causing algal blooms which impact wildlife, but also causes contamination of drinking water held in underground aquifers, which can be hazardous to human health.

Algae Bloom as a Result of High Levels of Nitrogen/Fertilizer Algae Bloom as a Result of High Levels of Nitrogen/Fertilizer

Nitrogen Found Present Decades Later

The study, led by Mathieu Sebilo from the Université Pierre et Marie Currie in Paris, France, and by Bernhard Mayer, professor of geochemistry and head of the Applied Geochemistry Group at University of Calgary's Department of Geoscience, found that three decades after crops had been fertilized with synthetic nitrogen fertilizer in 1982, about 15% of the nitrogen component still lingered in the organic matter present in the soil. After 30 years, approximately 10% of the fertilizer nitrogen had leached through soils and into groundwater, and is expected to continue to do for another fifty years or more.

The findings of the study, published recently in the Proceedings of the National Academy of Sciences of the United States of America, show that while nitrogen losses from fertilizer leach through soils at low rates, this continues over a number of decades. According to Mayer, “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. 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.”

Nitrates Most Widespread Drinking Water Contaminant

Because nitrates in drinking water can have serious health implications, nitrate levels in drinking water are regulated by both the United States and Canada. Surveys conducted by the EPA and the U.S Geological Survey in the 1980's reveal that nitrate contamination is the most widespread drinking water contaminant, affecting both domestic drinking water wells and public supply wells more than any other pollutant.

This is the first study to track the fate of fertilizer nitrogen that remains in soils over a number of decades using stable isotope 'fingerprinting'. Using N-15 – a stable isotope of nitrogen – as a tracer to monitor the fate of fertilizer nitrogen applied to crops of sugar beet and wheat in France in 1982, the scientists where able to measure the amount of N-15 labelled fertilizer nitrogen absorbed by plants over the thirty year period, enabling them to determine the amount of fertilizer nitrogen that remained in the soil and the long-term fate of the fertilizer nitrogen pool that is retained in soils.

The researchers found that

  • 61-65% of the N-15 fertilizer applied to the crops in 1982 was taken up by the wheat and sugar beet plants over the course of the 30-year study
  • 32-37% of the fertilizer nitrogen remaining in the organic content of the soil in 1985, three years after it was applied
  • 12-15% of fertilizer nitrogen still remained in the soil three decades later

Between 8-12% of the fertilizer nitrogen applied to the crops in 1982 had seeped down towards groundwater in the form of nitrate over the 30-year period, and will continue to leach through the soil at low rates “for at least another five decades, much longer than previously thought,” according to the study.

100 Years of Seepage

The researchers predict that approximately 15% of the fertilizer nitrogen that was initially applied to the crops will seep from soils into the groundwater over a time frame of about 100 years after the fertilizer was initially applied in 1982.

Mayer, who is internationally recognized as an expert in the field of using stable isotopes to track environmental contaminants, expects that if similar studies were conducted in Alberta, the results in terms of nitrogen retention within soils and fertilizer uptake by crops would be similar, however Alberta's drier climate and different geological characteristics may cause the rate of nitrate seepage into groundwater to be slower.

Nitrate contamination of water resources can be minimized if farmers follow the 4Rs when it comes to nutrient stewardship:

  • apply the Right fertilizer source
  • at the Right rate
  • at the Right time
  • and in the Right place

Journal Reference:

M. Sebilo, B. Mayer, B. Nicolardot, G. Pinay, A. Mariotti. Long-term fate of nitrate fertilizer in agricultural soils. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1305372110

3 thoughts on “Nitrogen Fertilizer Leaches into Groundwater for Decades ”

  • Jeanna Gollihur

    this is very interesting, I just got your post on fb...the deal here is that I live in the middle of wheat fields..thousands of acres of it, they fly over and spray fertilizer and herbicide, they drive over the fields and do the same..every year at least twice I get bad tummy, and I was hoping it wasn't the water from my well..what do you advise?

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