If nitrogen fertilizer wasn’t necessary for growing corn, how much would you save?
According to research from the University of Wisconsin, ancient relatives of modern commercial corn might hold another key to developing nitrogen-fixing corn varieties.
Why it matters: Corn that fixes a major portion of its own nitrogen could bring significant savings and environmental benefits.
If the right nitrogen-fixing traits could be incorporated into high-performing crop varieties, economic benefits for farmers in the form of lower fertilizer costs, as well as wider environmental boons through the reduction of nitrates in the ecosystem, could both be achieved.
Good corn yields require significant amounts of nitrogen. But since corn can’t fix atmospheric nitrogen, farmers worldwide often have to spend significant money on nitrogen fertilizer.
This reality doesn’t apply to everyone, however. According to Dr. Vania Pankievicz, a researcher from the University of Wisconsin’s bacteriology and agronomy departments, unique varieties of maize allow some Mexican farmers to regularly grow corn without any nitrogen fertilizer.
In the tropical regions of Mexico’s southern Oaxaca state, says Pankievicz, local producers grow Sierra Mixe maize — an indigenous landrace (locally created cultivar) — a very long season variety growing to about five to six metres in height. This landrace is grown year after year in nitrogen-lacking soils, and without nitrogen fertilizer.
In presenting to attendees at the Innovative Farmers Association of Ontario’s 2019 annual conference, Pankievicz said she and other university colleagues, including Dr. Jean-Michel Ané, the project’s lead researcher, now know the key to Sierra Mixe’s natural nitrogen success has to do with its ability to produce an abundance of “aerial roots” plus mucilage, a glycerin-like substance excreted from those areas of the stalk, and is rich in nitrogen-fixing bacteria.
Aerial roots are above-ground roots that grow from nodes on the cornstalk. While standard commercialized corn varieties produce small roots from about three nodes per plant, Sierra Mixe maize produces large roots from around 10 nodes per plant. Mucilage production is similarly much higher.
Constantly rehydrated by tropical rains, that mucilage drips onto the soil where the bacteria can make nitrogen available to the plant.
Pankievicz says the current hypothesis for the genetic origins of Sierra Mixe’s bacteria-filled mucilage production, and consequently, the ability to absorb nitrogen naturally, comes from Mexicana, an ancient maize ancestor common to both it as well as commercial corn. In modern varieties, she says, this trait was lost as new varieties were developed and grown in environments with high nitrogen pressure, that is, with lots of seasonally applied fertilizer.
What gene specifically allows Sierra Mixe and Mexicana to naturally absorb nitrogen has not yet been discovered. However, Pankievicz, says there is no reason the genetic characteristic can’t be reintroduced right now via traditional breeding with Sierra Mixe. This, she says, would be highly effective from a regulatory perspective (less biotech-related baggage) and prove to be the quickest way to commercialization.
Pankievicz believes the next step is to continue investigating how the trait works while starting a breeding program. Doing so, she says, would complement long-standing research initiatives looking for nitrogen-fixing bacteria strains that will associate with corn — as happens with legumes. Together, success in both research areas would help develop even less nitrogen-dependent yet commercially viable corn varieties.
Discoveries made with maize, too, could then be applied to other non-nitrogen fixing grasses and cereals.