By Andi Anderson
A recent study from Illinois reveals that adding nitrogen (N) fertilizer to soybeans often fails to improve yields. Researchers tested nitrogen applications on soybeans across nine sites between 2014 and 2017, including Urbana, Monmouth, Brownstown, and an irrigated farm in Chillicothe.
Soybeans need a large amount of nitrogen to grow—about 4.5 pounds per bushel—but usually get enough from soil and biological nitrogen fixation (BNF). BNF is a natural process where friendly bacteria in root nodules help plants absorb nitrogen from the air.
In the trials, researchers applied nitrogen at different growth stages and even tested a combination of all timings. Most of the time, soybean yields did not increase, especially in fertile, high-organic soils like those at Urbana and Monmouth. Sometimes, nitrogen even reduced yields.
At Brownstown, with its claypan soil and low organic matter, nitrogen applications made no positive difference. However, at Chillicothe’s irrigated, sandy soils, planting-time nitrogen increased yields by over 30% in two years.
Early nitrogen seemed to boost plant growth, which helped with nutrient uptake and root development.
Overall, results showed nitrogen is unlikely to benefit most Illinois soybean fields, especially when natural soil processes already meet the plant’s nitrogen needs. High-yield fields did not consistently respond to nitrogen, proving the common belief wrong.
The study suggests that only farmers on light, irrigated soils might test small strips of planting-time nitrogen for possible benefits.
With current market prices, spending on nitrogen for soybeans is usually not worth it. Farmers should focus on good management like balanced soil nutrients, timely planting, and weed control instead of adding unnecessary fertilizer.
Nitrogen fertilizer might seem like a way to ensure higher yields, but for most Illinois farmers, it’s a costly gamble with little return.
Photo Credit: gettyimages-fotokostic
Categories: Illinois, Sustainable Agriculture