When a farmworker sprays fertilizer over a field, there’s a good chance he or she will be outlived by nitrogen pollution from that fertilizer.
A 30-year study published this week in Proceedings of the National Academy of Sciences reveals that nitrogen could linger in soil for nearly a century after fertilizer is applied.
Nitrogen from fertilizer helps crops grow, but it can be poisonous for humans and animals. When nitrates leach from farmed soil into groundwater, they can make it undrinkable.
“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,” said researcher Mathieu Sebilo, the paper’s lead author.
Three decades after scientists applied fertilizer to sugar beet and winter wheat on two small experimental plots in France, they found that just 61 to 65 percent of its nitrogen had been gobbled up by the crops. Another 12 to 15 percent was still in the soil, and 8 to 12 percent had leached into the groundwater. (The scientists used a fertilizer with an artificially high concentration of a specific nitrogen isotope to help them track its movement over the decades.)
Based on those results, the scientists project that some of the nitrogen will still be lingering in the plots in another 50 years time.