Sponsored By
Prairie Farmer Logo

Lower nitrate levels linked to efficient corn productionLower nitrate levels linked to efficient corn production

University of Illinois study links efficient corn production with Illinois River water quality improvement; nitrate load 15% lower than Illinois Nutrient Loss Reduction baseline.

Jill Loehr

May 16, 2016

3 Min Read

Greg McIsaac, University of Illinois researcher, says there is a correlation between more efficient nitrogen use and improvements in Illinois River nitrate levels. McIsaac, lead author of the study, believes corn plants are more robust, using nitrogen more efficiently. “And farmers are better at judging how much fertilizer is needed,” McIsaac says.

“We think we’re seeing a positive impact on the river,” says McIsaac. “However, any takeaways should have a caveat. This is a correlational study; we’re fairly confident this is a cause and effect correlation, but we can’t be 100% sure.”


The goal of the study was to understand nitrate load and concentration changes over time as part of the Illinois Nutrient Loss Reduction Strategy. One possible source of change considered was nitrate in treated wastewater discharged into the Illinois River by the Water Reclamation District of Greater Chicago from 1983 to 2014. The authors also used annual records of fertilizer sales, livestock numbers, and crop yields to calculate residual agricultural nitrogen for each year; nitrogen made available to crops, but not utilized.

“The recent reduction in nitrate load in the Illinois River is a promising sign,” says McIsaac. The study was completed last October, before data for 2015 were available. “Now that these data are available, we know that the Illinois River nitrate load from 2011 to 2015 was 15 percent lower than the load measured in the baseline period from 1980 to 1996. This 15 percent reduction is a milestone that the state hoped to achieve for all its rivers by 2025,” he said.

Mark David, U of I biogeochemist and co-author of the study, says the residual agricultural nitrogen was highest in the late 1980s, following a major drought and low corn yields in 1988.

“Lots of unused fertilizer was left in the field,” McIsaac notes. “Fertilizer sales for the state have been fairly consistent since 1980, but corn yields have increased by 50%. So it’s clear that the amount of nitrogen being applied is more in tune to how much is needed and crops are more robust.”

McIsaac says even under drought conditions, such as 2005 and 2012, corn yields didn’t suffer like they did in the late 1980’s.  “Corn did much better in those years,” McIsaac notes. “More nitrogen ended up in corn versus the river.”

From their analysis of the data, the team found that annual nitrate loads were significantly correlated with river flow, nitrate discharged in Chicago wastewater and residual agricultural nitrogen averaged over a six year window. Nitrate concentrations – the average weight of nitrate in a typical gallon of river water – were also correlated with residual agricultural nitrogen and nitrate discharge from Chicago, but not river flow.

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.”

Nitrate concentrations, on the other hand, have declined more consistently since about 1990, which was a period of high concentrations. The reason for the divergence between nitrate concentration and load, explains McIsaac, is that the load is the product of both concentration and river flow and the flow is strongly influenced by precipitation, while concentrations are not. Higher flows allow the river to carry more pounds of nitrate, but it doesn’t necessarily change the concentrations.

Whether nitrate concentrations and loads continue to decline in the future depends on several factors, according to the researchers. “If the annual river flows return to their 1976-2005 average values, and if nitrogen fertilizer efficiency remains high or continues to improve, there likely will be a decline in nitrate loads in the Illinois River,” David explains. “On the other hand, if river flows remain high, which may be a consequence of climate change, meeting the nitrate reduction goals will likely require more conservation effort than originally proposed.”

About the Author(s)

Jill Loehr

Associate Editor, Prairie Farmer, Loehr

Subscribe to receive top agriculture news
Be informed daily with these free e-newsletters

You May Also Like