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In a 6-year trial, diverse cropping was a triple-win: less emissions, more income, more yields

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In a 6-year trial, diverse cropping was a triple-win: less emissions, more income, more yields

Simply adding sweet potato, peanuts, and soy crops to the regular wheat-maize mix across the North China Plain could offset national emissions by almost 6%, a new study found.
January 19, 2024

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Rotating crops with a diverse array of plants could increase yields by almost 40%, lock away almost 10% more carbon into the soil, and lower net greenhouse gas emissions by over 90%.

These striking findings come from an ambitious six-year field experiment on the North China Plain, a region that contains 70% of the country’s arable land and produces 23% of its cereal. It’s one of the most intensively-cultivated places in the world—and so is the perfect landscape to test whether changes to conventional farming practices could have a positive real-world impact. 

The researchers’ goal was to shake up the standard winter-wheat-to-summer-maize crop rotation by adding a few more crops into the mix—and then to see whether this arrangement benefited farmers’ bottom lines, and the environment. 

Among those crops, they tested sweet potato, a cash crop, and legumes like peanut and soybeans that are known to fix nitrogen into the soil. They reduced the conventional dose of synthetic fertilizer at these diversified sites to see how well they fared. Then, at each of their rotating test plots, they measured key traits linked to economic and environmental benefits: changes to yield and farmer incomes, greenhouse gas emissions, and soil health. These they compared with the same measurements taken from conventional plots of wheat and maize. 

Remarkably, plots that featured a rotating mix of sweet potato, wheat and maize showed increased yields of 38% compared to the conventional wheat-maize rotation. What’s more, general increases in yield associated with more diverse rotations were directly linked to farmers’ earnings—which peaked by 60% for plots with sweet potato rotations, and between 13 and 22% for crops that were mixed in with plantings of peanut and soy. 

Yield and income weren’t the only places where the researchers recorded gains. When they measured nitrous oxide emissions (N2O), phosphorus levels (both associated with fertilizer), and methane emissions from the test plots, they also noticed some large differences between sites.

 

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Compared to the wheat-maize controls, N2O emissions on plots that included rotations of peanuts, soybeans, and sweet potato were between 40 and 50% lower than in the wheat-maize control. Levels of phosphorus in the soil, too, were reduced. In some ways this wasn’t surprising, given that the researchers applied less synthetic fertilizer to those diversified plots. But the key takeaway is that this reduction clearly didn’t affect yields: the addition of nitrogen-fixing crops seems to build up a healthy soil profile for growing crops.

The researchers also found that all the test plots were net sinks for atmospheric methane, but in the diverse crop rotations, the strength of that sink increased by between 33 and 76%. 

These more promising emissions profiles may be linked to the overall health of the soil in plots that contained more types of crops. At the end of the epic six-year experiment, the researchers looked at multiple indicators of soil fertility—such as the amount of soil organic carbon, and the diversity of microscopic life in the soil—and compared them across the test sites. They found that not only was soil organic carbon higher in the diversified drop rotations, but so was microbial diversity, by about 10%, compared to the conventional plots. Since microbes can help trap atmospheric methane and sequester carbon in soil, that might help explain the more restrained emissions from those diversified plots. 

Finally, the researchers took those localized results and used an equation to project them across all agricultural land on the North China Plain. This painted a picture of potentially transformative benefits. 

Diversifying cropland rotations across the region would increase cereal production by 32%, and thanks to the inclusion of nitrogen-fixing legumes in the mix, more diversified plots would reduce the need for the application of synthetic fertilizers across the landscape by 3.6 million tonnes.

That’s the main reason behind the startling finding that, if farmers across China’s North Plain brought more crops into the mix, that action alone would offset almost 6% of the country’s annual greenhouse gas emissions—an impressive figure, considering this is just one farming region in China. Those farmers, meanwhile, would gain an annual 20% income increase, equivalent to $11.6 billion. 

China is at an inflection point, where several policies are being brought in to meet its climate and environmental targets—including one to transform farming into a net zero emitter by 2060, the researchers say. Their evidence adds real significance to the role that diversification and intercropping can play in reaching those goals, while elevating production and uplifting farmers, to boot. 

“We recommend that developing and adopting diversified cropping systems should be a key consideration in agricultural policy setting and a top priority for on-farm decision-making,” the authors write

Yang et. al. “Diversifying crop rotation increases food production, reduces net greenhouse gas emissions and improves soil health.” Nature Communications. 2024.

Image: ©Anthropocene Magazine

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