Researchers have found that a unique species of marine bacteria is just as effective at fertilizing agricultural soils as mineral fertilizers that are over-applied to croplands worldwide. And, these bacteria could do it with a fraction of the environmental cost that these other conventional fertilizers impose on the land.
The new NPJ Sustainable Agriculture study draws on the talent of a bacteria species native to the ocean called Rhodovulum sulfidophilum—or purple non-sulphur bacteria—for fixing nitrogen from thin air. Seeing this untapped potential, a team of scientists led by Kyoto University in Japan designed a set of experiments to explore whether this could be harnessed to more sustainably raise crops.
To start, they harvested the live bacteria, and then processed them to form a mash that could be dried to make a powder, easy to apply to growing crops. An analysis of the powdered contents showed that this mixture contained 11% nitrogen by weight, produced by the inventive bacteria, which was notably higher than the percentage in regular organic fertilizers like manure, or synthetic mineral fertilizers. But the high nitrogen content was no guarantee that plants could actually absorb it—that was the next phase of the experiment.
As their guinea pig for this step, the researchers picked Japanese mustard spinach, and applied the bacterial fertilizer to germinating seeds of the plants. They applied the fertilizer in different doses, ranging from two to 32 times the amount of a conventional fertilizer control.
Applying too little of the bacterial fertilizer made it ineffective compared with regular fertilizer, the experiment found, while too much caused growth defects in the plants. However, across the range of treatments, they discovered the sweet spot: applying the purple marine bacteria fertilizer at a rate four times that of conventional mineral fertilizer enabled the same amount of growth as conventional fertilizers, and without any risk to the plant. And not only did bacteria fertilizer at this treatment level not harm the plant, but it stabilized the soil condition as well: pH levels and salinity—usually unbalanced when too much fertilizer is applied—remained the same as the control, as if no nitrogen had been applied to the earth.
What’s more, specifically under warmer conditions the bacterial treatment actually led to crops with greater biomass than those that had been exposed to similar amounts of mineral fertilizer. “These results indicate that [the purple bacteria] could be used instead of a mineral fertilizer to obtain similar plant growth,” the researchers write in their study.
Synthetic nitrogen fertilizers are produced with fossil fuels through hugely energy-intensive industrial processes to force nitrogen fixation from the air. This makes them a major climate concern. In fact mineral fertilizers create almost 7% of the total greenhouse gas emissions attributed to global food production, which itself accounts for one-third of global emissions each year. So it’s worrying that fertilizer production is expected to increase by 50% in the next 26 years to keep pace with expanding croplands.
The nitrogen-scraping marine bacteria offer the chance to decouple fertilizer from these harms, the researchers say. “In the long term this could revolutionize agriculture and mitigate its negative impact on the environment.”
Numata et. al. “Utilization of lysed and dried bacterial biomass from the marine purple photosynthetic bacterium Rhodovulum sulfidophilum as a sustainable nitrogen fertilizer for plant production.” NPJ Sustainable Agriculture. 2024.
Image: ©Anthropocene Magazine
