Study: wheat roots release natural nitrogen inhibitors that could cut fertilizer use by 20–30%

Researchers at Aarhus University have identified seven naturally occurring wheat root compounds that suppress nitrifying soil bacteria as strongly as synthetic nitrification inhibitors, opening a potential breeding pathway toward wheat varieties that retain more applied nitrogen without requiring additional chemical inputs or yield sacrifice.

The nitrogen problem agriculture keeps confronting

Less than half the nitrogen applied as fertilizer is actually taken up by crops, with the remainder lost through leaching into waterways or gaseous emission into the atmosphere as nitrous oxide, a potent greenhouse gas. For decades the primary response has been regulatory limits on application rates and synthetic nitrification inhibitors, chemicals that slow the microbial conversion of ammonium to nitrate but are costly, require repeated application, and can affect non-target soil organisms.

The Aarhus team, led by postdoctoral researcher Purna Kumar Khatri, investigated whether wheat itself could perform a version of that function biologically. Their work centers on biological nitrification inhibition, a process in which plant roots release natural compounds that suppress the nitrifying microbes responsible for converting ammonium into the more leaching-prone nitrate form.

What are benzoxazinoids?

Benzoxazinoids are secondary metabolites produced naturally by cereal crops including wheat, maize and rye, traditionally studied for their role in plant defense against insects, weeds and nematodes. The Aarhus researchers screened 18 different benzoxazinoid compounds using a bioluminescence assay with Nitrosomonas europaea, a model nitrifying bacterium, and found seven — including BOA, MBOA, DIBOA and DIMBOA — capable of strongly suppressing nitrification at relatively low concentrations. Because these compounds are produced and released by the plant itself rather than applied externally, they offer a fundamentally different delivery mechanism than synthetic inhibitors: continuous, localized release exactly where and when the plant needs to protect available nitrogen.

Engineered wheat lines show the effect can be amplified

The study compared a conventional wheat parent line against two wheat lines carrying a chromosome fragment from Leymus racemosus, a wild grass known to enhance biological nitrification inhibition traits. Grown hydroponically, the enhanced lines released significantly higher concentrations of active benzoxazinoids than the parent line, and their root exudates suppressed nitrification up to twice as strongly — a result that correlated directly with the higher compound concentrations measured.

Modelling work cited by the researchers suggests biological-nitrification-inhibition-enabled crops could reduce nitrogen losses by 20% to 30%, and early field trials have shown no yield penalty associated with the trait, meaning farmers could in principle apply less fertilizer while harvesting comparable grain volumes. Khatri said the magnitude of the opportunity is significant even at modest efficiency gains: “If you can increase nitrogen-use efficiency by even ten percent in real field conditions, the absolute savings in fertiliser and emissions are enormous.”

From chemistry to a breeding target

The long-term goal is to translate the chemical findings into a breeding strategy: once researchers identify which biosynthetic pathways produce the most effective nitrification-inhibiting compounds, plant breeders could select for wheat varieties that express the traits more strongly, without requiring farmers to change practices or purchase new inputs. The research is part of the broader international CropSustain project, in which parallel research groups are studying how these traits affect soil microbiomes and non-target organisms over longer timeframes — a question that matters for regulatory and commercial uptake even if the underlying biology proves robust.

The findings arrive as global nitrogen markets remain volatile following the Strait of Hormuz disruption, which sent urea prices to near-record highs earlier this year before a partial correction. While breeding timelines for nitrification-inhibiting wheat varieties run on a multi-year horizon rather than offering immediate relief, the research adds to a growing body of biological alternatives — alongside microbial nitrogen-fixing products already commercialized by companies including Pivot Bio — that could gradually reduce the agricultural sector’s structural dependence on synthetic nitrogen inputs.

The study, “Benzoxazinoids as candidate compounds for biological nitrification inhibition in wheat,” was published in Plant Physiology and Biochemistry and conducted in collaboration with the University of Copenhagen, the University of Aberdeen, and Mexico’s International Maize and Wheat Improvement Center (CIMMYT), which provided seed material for the trial.

Source: EurekAlert / Aarhus University