by Emma Bryce at Anthropocene: 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.
