UK’s first measurements of nitrogen added by legumes to a crop production system

"The ability of beans to fix nitrogen from air presents an opportunity by which the environmental damaging impacts of excessive synthetic nitrogen fertiliser use may be avoided"

The potential of grain legume crops such as faba beans to harness the nitrogen present in air into biologically useful forms is well known, but how much of an opportunity does it present for farmers wanting to pursue net-zero agriculture? A research team from the James Hutton Institute has recorded the first UK-wide measurement of nitrogen added by faba beans. The study focused on a range of production systems, including the use of long-term crop-rotational data from the Institute’s Centre for Sustainable Cropping.

The team found that beans can incorporate more than 400 kg of nitrogen per hectare due to the symbiosis between legume crops and soil bacteria, which allows them to harness naturally occurring atmospheric nitrogen and negate the need for added synthetic nitrogen fertilisers. The crops also provide nitrogen to the production system after harvest and the residual stems, roots, and pods decay into the soil as a natural fertiliser, and general soil improver.

Prof Euan James, a research leader at the Institute’s Ecological Sciences department and co-author of the study, said: “These results are a first for Scotland and the UK and demonstrate that in addition to their value as a high-protein crop, beans can be used to help reduce costly and environmentally damaging fertiliser nitrogen inputs into arable systems.

“This demonstrates the huge potential grain legumes such as faba bean could provide in achieving zero-carbon agriculture, as well as meeting Scotland’s ambitious greenhouse gas emissions reduction targets.”

Dr Pete Iannetta added: “The ability of beans to fix nitrogen from air presents an opportunity by which the environmental damaging impacts of excessive synthetic nitrogen fertiliser use may be avoided.

“We are fortunate to have the incredible long-term whole-system datasets of the Centre for Sustainable Cropping, which is managed by Dr Cathy Hawes. There is nothing like it globally for agroecological studies of arable cropping.

“This, allied to a fantastic team of collaborators from across the UK, including farmers – has allowed us to achieve a strong foundation for future environmental impact assessments.”

The James Hutton Institute’s Centre for Sustainable Cropping was established in 2009 to design an integrated cropping system for multiple benefits and test the long-term impacts on biodiversity and whole-system sustainability. By enhancing soil quality and reducing dependence on fertiliser inputs, researchers at the CSC are looking at how to minimise pollution and losses through run-off, leaching, erosion and greenhouse gas emissions. For more information on the CSC, including a virtual tour, visit csc.hutton.ac.uk.  

Paper: Maluk, M., Ferrando-Molina, F., Lopez del Egido, L. et al. Fields with no recent legume cultivation have sufficient nitrogen-fixing rhizobia for crops of faba bean (Vicia faba L.). Plant Soil (2022). https://doi.org/10.1007/s11104-021-05246-8