Herbicides have become a key agricultural ingredient for our globalized food systems, but they also create a catch-22. While on the one hand they tackle weeds, they simultaneously weaken the soil quality and organic material that crops need to thrive. Ironically, like the weeds themselves, this threatens yields. Now, researchers think they have found a solution that not only deals with weeds and boosts crop yields, but also reduces the amount of chemical herbicides that farmers need to apply in the first place.
This triple-win is built on the back of microscopic organisms: tiny ‘rhizobacteria’ that survive in the root ecosystems of plants. Dozens of studies have explored the unique benefits of these bacteria, which can range from helping crops fix nitrogen from the soil, to fighting off pathogens. Rhizobacteria support plants essentially by building up a healthy microbiome in and around their roots.
But the new Soil Ecology Letters study is the first to also explore how, by boosting yields, they might also reduce the need for excessive herbicides.
The researchers went into the experiments with a selection of root bacteria from the Pseudomonas genus, a group known for its ability to suppress growth in agricultural weeds. They cultivated a number of bacterial species in the lab, and then narrowed the most promising candidates down to four, which they tested on wheat plants.
First, they tested these in a set of greenhouse experiments, which revealed that when combined with a low dose of herbicide those four species all successfully suppressed the growth of a weedy grass called Phalaris minor that regularly plagues wheat fields in Pakistan, where the research took place. The greenhouse experiments also showed that the bacteria improved the yields of the wheat, compared to controls where only the herbicide was applied.
With this success, the researchers moved their experiment out into the field, testing the bacteria alongside different doses of herbicide on the wheat crop, ranging from 25%, to 50%, and 75%. They compared this bacteria-herbicide combo with a field where wheat only received herbicide and no bacteria in the mix.
Strikingly, this revealed that wheat plots that were treated with the bacteria-herbicide combo were able to control weed growth even better than those treated with herbicide alone. Things grew more interesting when the researchers looked again at yield, showing that when combined with doses of 50% and 75% herbicide only, the bacteria still managed to keep weeds suppressed, while simultaneously boosting wheat yields, compared to the control plots.
In other words, when it was also inoculated with the bacteria the wheat actually grew better with less herbicide in the mix. This suggests that at those specific ratios the bacteria and agricultural chemicals work synergistically. In fact, the study calculated that plots treated with a lower dose of herbicide paired with bacteria gained up to 22% of the grain that was lost on the regular herbicide-only plot.
The researchers think this might be because the growth-promoting qualities of the root bacteria help to offset any potential lost benefit of the weed-suppressing herbicide. This could benefit yields over the long term as well, by allowing farmers to reduce the amount of herbicide they apply, thus taking some chemical pressure off the soil and enabling it to gradually regenerate the nourishing qualities that boost crops.
Not only that, but curbing the application of chemicals could also help to tackle the global challenge of herbicide resistance that increasingly plagues global agriculture: over 160 herbicide products worldwide have been rendered useless by this problem. Weaning farms off herbicide would also have knock-on benefits for the wider ecosystem, where the overuse of these chemicals poses real threats to freshwater habitats and biodiversity.
In an ideal world, farmers would be able to achieve high crop yields at large scales without the use of chemical additives. But, this study suggests that in the meantime, a lot of good can be achieved by dialing back the amount we apply to the land—something that’s now possible with this integrated herbicide-bacterial approach.
Gao, et. al. “Integrated application of synthetic community reduces consumption of herbicide in field Phalaris minor control.” Soil Ecology Letters. 2023.
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