On a quiet weekend morning in a greenhouse in AU Flakkebjerg, rows of wheat plants stand growing with their roots submerged in clear water. There is no soil, no buffer, no automation to take over the work. Every day, weekends and holidays included, Postdoc Purna Kumar Khatri comes by to check them. He adjusts the pH drop by drop. If he does not, the roots will suffer. And the experiment will fail.
“It’s physically demanding,” he says, “but also mentally. You have to be precise. Every single day.”
This meticulous routine is part of a much larger story: one that begins beneath the soil surface, where plants quietly negotiate with microbes over one of agriculture’s most precious resources: nitrogen.
The nitrogen problem that we continue addressing
Modern agriculture runs on nitrogen. Yet less than half of the nitrogen applied as fertiliser is actually used by crops. The rest is lost through leaching or gaseous emissions into the atmosphere as nitrous oxide.
For decades, researchers and policymakers have tried to manage this problem with regulations and fertiliser limits. Another way to limit the problem is synthetic nitrification inhibitors. These chemicals slow down the microbial conversion of ammonium to nitrate, which can reduce nitrous oxide emissions by limiting nitrification and subsequent denitrification, but they are costly, must be reapplied, and may affect non-target soil organisms.
What if plants themselves could do the job?
This is the core idea behind biological nitrification inhibition (BNI): a process where plant roots release natural compounds that suppress the activity of nitrifying microbes in the soil. The result: more nitrogen remains in a form plants can use, less is lost to the environment, and fertiliser efficiency improves.
“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.”
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