28 February 2024

Legumes can offer a solution for sustainable agriculture


Crucial is the ability of legumes to fix nitrogen, an essential element for ensuring soil productivity. In Cambridge, a team of researchers is studying this dynamic to understand how to reduce the use of chemical fertilizers

by Matteo Cavallito


Legumes cooperate with microbes to fix nitrogen in the soil, enriching it with essential nutrients. This characteristic obviously attracts the attention of scientists who, precisely through observing these plants, hope to improve soil yields by reducing the use of fertilizers. This is explained by Sebastian Schornack, research group director of the ENSA (Enabling Nutrient Symbioses in Agriculture) project at Cambridge University on the Australian website The Conversation.

The ability to fix nitrogen is crucial

About 100 million years ago, the professor explains, legumes developed the natural ability to host certain bacteria within dedicated structures called root nodules. Here the microorganisms convert the nitrogen in the air and soil into a form accessible to the plant, which uses it as nutrients. Because of this special feature, leguminous plants need less nitrogen fertilizer than other crops.

“A high-performing legume can fix up to 300kg of nitrogen per hectare, which would otherwise cost farmers around $1 per kg in fertiliser to meet the nutrient needs of the plant,” Schornack writes.

Moreover, he says, “At the ENSA project, we are exploring how these nitrogen-fixing root nodules evolved in only legumes in the first place. With that knowledge, we hope to find ways to increase the efficiency of nitrogen fixation inside the root nodules and maximise the growth and yield of legume crops.”

Extending the dynamics of legumes to other crops

Studies focus on the ability of legumes to interact with beneficial bacteria while keeping harmful microbes at bay. It is precisely the need to defend against pathogens that may limit the plant’s ability to fully engage with more beneficial microorganisms. It therefore becomes essential, the researchers argue, to fully understand the weight of these limiting factors. “The benefits of more efficient nitrogen fixing in legumes would include greater growth and biomass and, we hope, higher protein content in the seeds or pulses,” Schornack writes.

More efficient plants also imply reduced use of nitrogen fertilizers with a positive impact on soil health. This is also why scientists have long aspired to extend the dynamics observed in legumes to other crops.

“The more we know about this unique ability of legumes, the greater our chance of successfully developing other crops with a similar ability,” the professor continues. “Such a development, though some years away, could transform sustainable agriculture, especially in areas where access to synthetic fertiliser is already limited by cost and availability.”

Balance is needed in nitrogen management

Research once again calls into question the need to strike a balance in overall nitrogen management. This element, as is well known, remains valuable and essential for crops. But its excessive accumulation, also linked to the massive use of fertilizers, can ultimately be dangerous for the environment.

Indeed, nitrogen loss in fields impacts soil and water, has harmful effects on plants and animals, and contributes to smog and climate change.

Attention to these issues has been growing in recent years. It is no coincidence, for example, that the European Commission has reiterated the need to account for the entire greenhouse gas balance, including the nitrous oxide released in the calculation. Available solutions, experts note, include the use of better technologies and the application of more efficient fertilization practices.