BYLINE: Lauren Quinn
Newswise — URBANA, Ill. — Let’s say you’re a corn grower farming on low-fertility soil. How do you go about making that soil healthier and more fertile? Many farmers think if they add plenty of nitrogen fertilizer, that nutrient, along with carbon, will be stored in the soil as organic matter when microbes decompose crop residue. But new research from the University of Illinois suggests those efforts might not work for poor soils.
The new study, published in the Soil Science Society of America Journal, compared corn residue decomposition in high- and low-fertility, with and without nitrogen fertilizers. The results came as a surprise.
“Corn residue decomposed significantly faster in poor, low-nitrogen-supplying soils compared to a fertile soil, especially when we added nitrogen, which stimulated microbial activity. It was a surprise, based on our earlier findings that showed high-nitrogen corn residue broke down faster,” said study author Tanjila Jesmin, doctoral researcher in the Department of Natural Resources and Environmental Sciences (NRES), part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at U of I.
Richard Mulvaney, professor in NRES and study co-author, explained poor soils have fewer aggregate particles, small craggy nuggets that house soil microbes and give soil its structure. With fewer aggregates, free-wheeling microbes roam loose in the soil, encountering carbon more frequently, gobbling it up, and creating carbon dioxide as a byproduct.
“In a poor soil with less aggregate stability, microbes have greater access to the residues and the carbon. And when there’s a high nitrogen supply, they also have a high demand for carbon as an energy source. Eventually, their demand may exceed the carbon supply in residues, which may cause them to attack organic matter in the soil,” Mulvaney said. “The microbes just keep burning it and evolving more carbon dioxide. It’s a downward spiral.”
To learn how soils of contrasting fertility mineralized carbon in the presence of corn residue, Jesmin performed a soil incubation study in the lab. She collected two soils of the same type from production fields in Central Illinois, one with high native nitrogen content and one depleted in nitrogen after 70 years of continuous cropping. She also collected