Researchers have been making headway in their analysis of a rare variety of maize that is able to fix nitrogen to its roots; a discovery which has the potential to make all nitrogen fertilizers unnecessary.
While fertilizer experts understand how beans and pulses fix atmospheric nitrogen, we still have much to learn if we want to use less fertilizer. As Alan Bennett, professor of plant sciences at the University of California, Davis, notes, “Legume crops like soybeans have nodules on their roots that harbour bacteria that can turn nitrogen in the air into a form the plant can use. However, for cereal crops like corn, farmers must rely primarily on nitrogen fertilizers.”
In the United States, more than 90 million acres of corn are planted every year. Corn uses more land than any other crop.
According to the science journal Scientific American, “Over 5.6 million tons of nitrogen is applied to corn [also known as maize] each year through chemical fertilizers, along with nearly a million tons of nitrogen from manure.”
Corn was originally domesticated by indigenous Mexican peoples 10,000 years ago, and over the millennia some varieties were cultivated and selectively developed to grow in poor quality soil without the aid of fertilizers. The plants could grow in such difficult conditions because of their above-ground roots that could fix atmospheric nitrogen.
Decades ago, agricultural scientists found a number of these special varieties of corn (called landraces) in isolated villages in the Sierra Mixe region near Oaxaca, but they were unable to fully understand how the specialised root nodules worked.
Now, a team of researchers from the University of California, Davis, has used modern chemistry techniques to prove that these specialized varieties of maize can take as much as 82% of their nitrogen requirements from the atmosphere. As the UC Davis website reports, “the corn grows a series of aerial roots. Unlike conventional corn, which has one or two groups of aerial roots near its base, the nitrogen-fixing corn develops eight to ten thick aerial roots that never touch the ground.
During certain times of the year, these roots secrete a gel-like substance, or mucilage. The mucilage provides the low-oxygen and sugar-rich environment required to attract bacteria that can transform nitrogen from the air into a form the corn can use.”
The aerial roots of Sierra Mixe maize secrete large quantities of mucilage between 3 and 6 months after planting. The mucilage is carbohydrate rich, with the composition dominated by arabinose, fucose, and galactose. Credit: Plos One
“We have shown this [nitrogen fixation] through growth of the plant both in Mexico and Wisconsin,” adds co-author Jean-Michel Ané, professor of agronomy and bacteriology in the College of Agricultural and Life Sciences at UW–Madison.
Another co-author, Howard-Yana Shapiro, the chief agricultural officer at Mars, Inc, is equally proud of the team’s work when he said, “This research has been 40 years in the making and is a significant breakthrough in our attempts to find a more sustainable way of growing corn, one of the world’s key crops.”
The researchers have now published their findings in the journal Plos One where they report that, “… the mucilage associated with the aerial roots of Sierra Mixe maize can support a complex diazotrophic microbiota … and that nitrogen is transferred efficiently from the nitrogen-fixing bacteria to the host plant tissues.”
While at present the analysis is focused on the very important crop of corn, the possibility of expanding nitrogen fixing abilities into other species is equally exciting. As the researchers add, “It will be interesting to explore if aerial roots produced by other cereals such as sorghum can perform a similar function.”
The team also notes the discovery’s massive potential, stating that, “This research suggests new avenues for research into potentially novel mechanisms of biological N2 fixation in maize. This could have a significant impact on maize crop productivity and nitrogen use efficiency, particularly in regions of the world where agriculture is characterized by poor soil nutrition.”
While farmers in the developed world may be excited at the prospect of saving money on nitrogen fertilizers, those in poorer countries will be even more enthusiastic. Farmers in the developing world often have to work with low-nutrient soil without access to any fertilizer. If fertilizers can be sourced they are often much more expensive than those available in Europe or America due to trade bureaucracy, inefficient supply chains and logistics, and the distances from fertilizer producer to field.
As co-author Allen Van Deynze, director of research at the UC Davis Seed Biotechnology Center, observes, “Corn yields in developing countries are one-tenth of those found in the U.S., due both to variety development and access to affordable nitrogen fertilizer. This discovery opens the door to significantly improving the genetic potential and food security for these countries.”
The development of nitrogen fixing corn would also aid the fight against climate change as at present 1%-2% of global energy is spent producing fertilizer.
The researchers freely admit that there is still much work to be done, but the prize is clearly worth it. The benefits of developing cereal crops that can fix atmospheric nitrogen would aid the environment, help feed global population growth, combat global poverty and famine, and make food everywhere cheaper.
And it could also be the end of the fertilizer industry.
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Photo credit: UCDavis, Kusamala, CommonsDream, & PlusOne.
