WASHINGTON, May 25, 2016 - The more efficient use of nitrogen fertilizer in agriculture has yielded positive results not just for water quality in the Mississippi River Basin, but for corn yields too, according to research out of the University of Illinois.
The study’s authors found that the amount of nitrogen runoff making its way into the Illinois River (part of the Mississippi River Basin) between 2011 and 2015 was 15 percent less than the average runoff measured between 1980 and 1996 – marking a reduction milestone Illinois set out to achieve in all its rivers by 2025.
The decrease in nutrient pollution may be tied to reductions in the amount of nitrate discharged from Chicago’s water treatment plants into the Illinois River, and reductions in residual agricultural nitrogen levels – the amount of nitrogen left in the soil after harvest – which began to decline in the basin around 1990, the study found.
The lower runoff and residual nitrogen levels could be explained by the more efficient use of fertilizer. For instance, fertilizer sales went stagnant starting in 1980, while corn yields in the watershed increased by 50 percent between 1980 and 2015.
One of the study’s co-authors, U of I biostatistician George Gertner, said the correlations his team found between agricultural runoff and pollution levels in the river were statistically significant and “strongly suggestive” that the two are connected. However, he said, the study didn’t generate “definitive proof that the reductions in residual agricultural nitrogen or nitrate discharge from Chicago caused changes in nitrate concentrations or loads in the river.”
That’s in part because nitrate loads are strongly influenced by precipitation and river flow, which can be highly erratic.
“It is promising that nitrate loads have declined in recent years despite higher than average river flows. The five-year average river flow from 2007 to 2011 was the highest recorded since the start of measurement in 1939,” said Greg McIsaac, U of I researcher and lead author of the study.
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