As climates around the world grow harsher and increasingly unpredictable, concerns are increasing over our world's food security.

Already, yields of staple crops like maize and wheat are dropping in low-latitude tropical regions and in dry and drying regions such as African drylands and parts of the Mediterranean.

Wealthy countries are far from immune. Australia experienced almost a 30 percent crop yield decline between 1990 and 2015 due to reduced rainfall.

While studying food diversity in 2011, environmental scientist Morgan Ruelle, now at Clark University, accidentally stumbled across one possible technique that could help stabilize dipping crop yields.

The once widespread practice is now only used by small farms in places like Caucasus, Greek Islands, and the Horn of Africa. Despite being incredibly simple, most of the agroecology community weren't aware of it.

Yet farmers have been using this technique for more than 3,000 years across at least 27 countries. It may have even been what gave rise to agriculture in the first place.

The method is planting maslins – a combined mix of cereals that can include rice, millet, wheat, rye, barley and more – and harvesting them all together to be separated or used as a single product.

In Ethiopia, for example, where Ruelle discovered the existence of maslins, duragna contains multiple species and varieties of barley and wheat, all grown together. The locals consider the mix to be one crop, using it to make bread, beer and traditional savories with it.

Local farmers reported this mix ensures at least some yield under unfavorable conditions, and now researchers have the experimental trials to back up these claims. Working at Cornell University, Ruelle and colleagues conducted a review of previous work, demonstrating maslins yielded higher stability under changing conditions. By shifting species composition each season, farmers could hedge against climate impacts without the need for additional intervention.

"It's this continuously evolving responsive entity. On its own, it's operating outside the farmer's control to respond to whatever conditions happen," says Ruelle. "So no matter what, you're going to be able to make bread with this."

The process lets the environment choose which species will thrive. And if environmental conditions continue to shift in one direction, the mix of seeds for the next season will also shift in line with that trend too.

"It's more rapid than evolution. If you had just one weak variety, it would take a long time to adapt," explains ethnobotanist Alex McAlvay now at the New York Botanical Garden. "But if you have multiple species and multiple varieties, those shifts can happen very rapidly."

When drought strikes, the resulting crop yield will contain the more drought resistant strains of barley, and less wheat for example. But the wheat is still there to take over if there's a sudden wet season.

"If one fails, at least we have the other," a Georgian priest growing this mix told one of the researchers in 2022.

For some time now researchers have been advising a shift away from monoculture farming may be beneficial in many cases, as planting multiple types of crops is far better for pest management, fertilization, wildlife health and sustainability. However, polyculture is problematic for larger scale farming that relies on machinery for harvest and processing.

Since the same machinery can be used to harvest each variety of grain within the maslin mix, the process can be scaled up. Modern industry is experienced at sorting grain types on a large scale too.

Maslins also produce higher yields. In a field trial wheat and barley together did 20 percent better than wheat by itself and 11 percent better than barley by itself, and another study found the monoculture land use would have had to be increased by 50 percent to achieve the same result for the same maslin mix across three years.

What's more, maslins still convey many of the ecological benefits of polycultures involving entirely different plant types, such as resistance to diseases and pest insects which would require less reliance on the pesticides that are causing all sorts of harm to wildlife.

"I've talked to some Israeli scientists who said that they never find wild wheat without wild barley," says McAlvay. "These grains have been co-evolving for many, many thousands of years."

There's also evidence that early farmers in the Bronze Age and Neolithic periods used maslin mixtures like emmer and spelt or einkorn.

"A mixture of wild barley (Hordeum spontaneum) and wild oat (Avena sterilis) was being cultivated at Gilgal in Israel, before either was domesticated," the researchers write in their paper.

While there are still a lot of uncertainties to investigate, like the tolerance different mixes might have to poor soils, McAlvay and team believe maslins could provide huge benefits across all levels of farming, from subsistence to industrial, particularly in areas already facing challenging climate conditions.

"Subsistence farmers around the world have been managing and mitigating risk on their farms for thousands and thousands of years and have developed these locally adapted strategies to do that," concludes McAlvay. "There's a lot we could learn from them, especially now, in a time of climate change."

This review was published in Agronomy for Sustainable Development.