Legume crops boost nutrition while protecting the environment

In a new study published by Frontiers, experts have determined that adding beans and other legumes to crop rotations could be key to more sustainable and nutritious food production.

The study provides some of the first evidence that complementing traditional crop rotations with legumes produces both environmental and nutritional benefits. 

“This strategy can contribute significantly to the specific European Union Green Deal Farm to Fork objectives to reduce greenhouse gas emissions, chemical pesticide use and synthetic fertilizer use,” said study first author Marcela Porto Costa of Bangor University. 

“For example, in Scotland, we’ve shown that the introduction of a legume crop into the typical rotation reduced external nitrogen requirements by almost half whilst maintaining the same output of food measured in terms of potential human nutrition.”

Nitrogen is considered the most important nutrient for plant growth. For most crops, farmers use fertilizers to provide nitrogen. However, chemical fertilizers have harsh environmental consequences, polluting the surrounding water and air and depleting the soil of minerals. 

The European Union Green Deal Farm to Fork strategy aims to address the issue with a goal of cutting greenhouse emissions and chemical pesticide use by 50 percent, as well as reducing synthetic fertilizer use by at least 20 percent by 2030. 

Legumes are among the only crops that are capable of naturally absorbing all of the nitrogen they need. These crops have a symbiotic relationship with bacteria that transform atmospheric nitrogen into a form that can be accessed by plants.

Beans and other legume crops not only enrich the soil with nitrogen without the need for fertilizer, but also reduce the need for nitrogen fertilizers for future non-legume crops.

Overall, legumes are one of the most nutrient-rich crops, containing protein, fiber, folate, iron, potassium, magnesium and vitamins.

The researchers took a new approach to calculating the environmental footprint of crops by comparing 10 crop sequences using 16 different impact categories. The team assessed crops over three to five years in three European climates across Italy, Romania,  and Scotland.

“Our innovative approach goes beyond simple food footprints by looking at the footprint of delivering a specific quantity of human, or livestock, nutrition from all crops produced within representative crop rotations,” said Dr. David Styles of the University of Limerick. “This provides a clearer picture of inter-crop effects and the overall efficiency of different cropping sequences in delivering nutritious food (or livestock feed).”

So far, the experts have only established the potential nutritional benefits of adding legumes to crop rotations. Ultimately, this will depend on how foods are processed and sold. 

“Our results strengthen evidence on the positive role that healthy diet transitions could make to environmental sustainability,” said Styles. “Legumes provide a healthier balance of carbohydrates, protein and fiber compared with cereal crops, and could improve the nutritional profile of the food we eat.”

“These results also highlight the need for whole-system (multi-crop, farm-to-fork) thinking when designing interventions to drive sustainable food systems so that we can deliver better nutrition whilst reducing environmental impacts,” said Costa.

The study is published in the journal Frontiers in Sustainable Food Systems.

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By Chrissy Sexton, Earth.com Staff Writer