By Andi Anderson
A study by researchers at the University of Illinois Urbana-Champaign found that nitrogen fertilizer provides limited benefits to high-yielding soybeans. Soybeans naturally partner with bacteria that convert atmospheric nitrogen into a form the plants can use.
This partnership, along with nitrogen from the soil, generally meets the crop’s needs, even with increasing yield potential.
Soybeans are a high-protein crop, requiring significant nitrogen to produce proteins. Some farmers and researchers believe that adding nitrogen fertilizer could help meet this demand, especially as yields continue to rise. However, ongoing field trials suggest otherwise.
The research team, led by Professor Emeritus Emerson Nafziger, conducted nine field trials across Illinois from 2014 to 2017, applying nitrogen at various stages of soybean growth.
They found that while applying nitrogen at all stages increased yields slightly, the gains were not enough to justify the high cost of fertilizer. “Any treatment that costs two to three times the value of the extra production is a sure way to lose money,” Nafziger said.
The study showed no consistent yield benefits from nitrogen applied during flowering, pod setting, or seed filling. Assistant Professor Giovani Preza Fontes noted that nitrogen availability during critical growth stages was not a significant limitation for yield.
There was one exception: a single nitrogen application at planting increased yields in specific conditions, such as lighter soil with low organic matter.
This effect was seen in a loam soil field in Chillicothe, Illinois, where nitrogen at planting improved early growth and reduced symptoms of sudden death syndrome, a fungal disease.
Despite this, researchers caution against using nitrogen fertilizer widely. Soybeans typically thrive without it, and the nitrogen-fixing bacteria and soil bacteria generally supply what is needed.
Nafziger advises that nitrogen fertilizer should only be considered in areas where soybeans struggle to grow early due to soil conditions, suggesting that farmers can experiment on small plots to see if it makes a difference.
Overall, the study reinforces that nitrogen fertilizer is not usually necessary for soybeans, which can achieve high yields without the additional expense and environmental impact of extra nitrogen.
Photo Credit: istock-urpspoteko
Categories: Illinois, Crops, Soybeans