BNI wheat research at AU Flakkebjerg is revealing how root compounds may help cereal crops use nitrogen more efficiently. The work could support future wheat varieties that maintain yield with less fertiliser and lower nitrogen losses.
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Natural compounds released by wheat roots may help crops keep more nitrogen in the field, offering a biological path to lower fertiliser use and reduced emissions.
In a greenhouse at AU Flakkebjerg, rows of wheat plants grow with their roots suspended in clear water. Every day, including weekends and holidays, Postdoc Purna Kumar Khatri checks the plants and adjusts the pH drop by drop.
“It’s physically demanding,” he says, “but also mentally. You have to be precise. Every single day.”
The work is part of a larger effort to understand how wheat and other cereal crops can use nitrogen more efficiently.
Keeping Nitrogen in the Field
Less than half of the nitrogen applied as fertiliser is taken up by crops. The rest can be lost through leaching or released as nitrous oxide, a greenhouse gas.
Researchers are studying biological nitrification inhibition, or BNI, a process in which plant roots release natural compounds that slow the conversion of ammonium into nitrate. That can keep more nitrogen available to crops and reduce losses from the field.
“Plants are not passive,” Purna Kumar Khatri explains. “They have strategies. They defend themselves. And they try to secure nutrients in the soil. We are just beginning to understand how sophisticated those strategies are.”
Natural Compounds With a New Role
Khatri’s research focuses on benzoxazinoids, natural compounds found in cereals such as wheat, maize and rye. They are already known for helping plants defend against insects, weeds and nematodes, according to a press release.
In a new study, researchers screened 18 benzoxazinoids using Nitrosomonas europaea, a model nitrifying bacterium. Seven compounds, including BOA, MBOA, DIBOA and DIMBOA, strongly suppressed nitrification at relatively low concentrations.
“It was good news,” Purna Kumar Khatri says. “Not because the compounds were completely unknown, but because now we understand them better. They were already known as defence chemicals. Now we see that they may also be key players in nitrogen management.”
BNI Wheat Shows Promise
The study compared a conventional wheat parent line with two BNI wheat lines carrying a chromosome fragment from the wild grass Leymus racemosus, known to enhance BNI traits.
The BNI wheat lines released higher amounts of active benzoxazinoids than the parent line. Their root exudates inhibited nitrification up to two-fold more strongly.
“If you can increase nitrogen-use efficiency by even ten percent in real field conditions,” Purna Kumar Khatri says, “the absolute savings in fertiliser and emissions are enormous.”
Breeding for Better Nitrogen Use
For crop production, the goal is to develop wheat varieties that can maintain yield with less fertiliser. Some modelling studies suggest BNI-enabled crops could reduce nitrogen losses by 20–30 percent, while early field experiments show no yield penalty.
“The plant produces very small amounts,” Purna Kumar Khatri explains. “But it does so continuously. And these chemicals have been part of natural ecosystems forever. They are not something new we introduce from outside.”
The next step is breeding wheat varieties that express these traits more strongly.
“This is where chemistry meets genetics,” he says. “Once we know the compounds, breeders can work on enhancing the plant’s capacity to produce them.”
A Biological Route Forward
For now, the work continues in the greenhouse, where root exudates are collected, frozen and analysed. The process is slow and repetitive, but it could help point the way toward cereal crops that need less nitrogen fertiliser to produce the same yields.
“If you break a cycle naturally,” Purna Kumar Khatri says, “not with chemicals but with biology, then everyone benefits: the plant, the farmer, and the environment.”
Collaborators include Aarhus University, Copenhagen University and the University of Aberdeen.
The work is supported by the Novo Nordisk Foundation under the Biological Nitrification Inhibition project, BioNI, and in collaboration with CIMMYT under the CropSustaiN/AU-AGRO project. CIMMYT provided the seeds for Roelf parent and Roelf BNI wheat lines used in the study.
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