Intercropping for protein yield resilience: peas, beans and cereals in a changing climate

Through our company’s involvement in the Nitrogen Climate Smart (NCS) Project, Kelvin Cave works with many industry partners in the drive to increase the national acreage of home-grown proteins. One partner, The James Hutton Institute, is assessing the value of legumes across intercropping systems. Here, two scientists working on the project, Pete Iannetta and Sam Holden, report on their early findings including how they have increased yield, lifted protein and mitigated risk.

Intercropping – the practice of growing two or more crops together in the same field at the same time to optimise and assure yields with less inputs – is gaining attention. This interest extends beyond traditional pulse-cereal combinations, to pulse-pulse mixtures as a practical way to manage risk, reduce fertiliser inputs and improve home-grown protein production. Recent work on pea-bean combinations, alongside pulse-cereal mixtures, is beginning to show where the real opportunities lie, and where more work is still needed.

Three pea-bean intercrop trials have recently been completed and are under assessment, focusing on nitrogen-fertiliser use offset and following crop effects due to difference in crop-stand density and varietal choice. Alongside this, wider work on pulse-cereal mixtures has explored how winter- and spring-sown legumes grown with cereals can deliver protein yield either as grain, or as wholecrop forage. Together, these studies are helping build a clearer picture of what intercrops can offer on farm.

Pea-field bean intercrops

The early message for pea-bean intercrops is encouraging and realistic. Intercropping peas and beans can increase yield, although the benefits are conditional and not guaranteed. In other words, it works well in some combinations and situations, but not all. Stand density plays a major role, and trials show that beans should dominate the intercrop for highest protein yields, since higher bean density raises overall yield while higher pea density can compromise yields due to competition effects, shattering, and lodging.. It is therefore not surprising that peas in this intercrop appear to perform best at lower stand densities when grown with beans.

This has clear practical implications. Simply mixing two full-rate crops together is unlikely to give the best result. Instead, careful adjustment of relative seed rates is essential; and variety choice also matters. Some combinations consistently performed better than others. In particular, the pea variety Mantara, especially when combined with the bean variety Ketu, showed strong and consistent intercrop performance. This suggests that compatibility between varieties is critical in terms of growth habit, maturity and competitive balance. It is not just about species choice, but about which cultivars are paired.

However, the yield advantage of intercrops needs to be considered carefully. Land Equivalent Ratio (LER) values above 1 indicate a land use benefit (ie: more yield per unit area compared to a monocrop), but when pea pre-harvest losses (due to pod shatter) were included, the apparent intercrop advantage was reduced. This is important for farmers, since if some pea varieties are more prone to pod shatter or harvest losses in a mixed canopy, some of the theoretical gain may be lost at the combine. Management and machinery settings will therefore be just as important as biology.

Beyond yield alone, soil nitrogen outcomes are also a major focus. In the pea-bean work, and soon after harvest, moncropped beans appeared broadly nitrogen neutral, while peas and intercrops were nitrogen positive. There is also evidence of distinct species-led residue mineralisation patterns, with pea residues releasing nitrogen earlier, suggesting altered post-harvest nitrogen returns. In practical terms, this could influence nitrogen availability to the following crop and affect fertiliser planning.

Pulse-cereal intercropping

This links directly to the wider pulse-cereal work. In winter-sown systems, faba bean grown alone or with wheat produced some of the highest wholecrop forage yields, in the range of 12 to 15t/ha, though from plot scale trials (which generally tend to over-estimate potential commercial scale yields). These were around 30% higher than the best spring wholecrop yields. When harvested as wholecrop, winter bean-wheat mixtures delivered very high protein yields, and importantly, they did so without the need for 50kg N/ ha of synthetic nitrogen fertiliser. In spring-sown systems, a different picture emerged. The highest grain yields, around 8-10t/ha, came from pea-wheat mixtures. Again, these yields were achieved without clear benefit from additional synthetic nitrogen.

In contrast, spring faba bean struggled in the shortened and drought-affected season (2023). This underlines a key point that producers know only too well: performance depends strongly on season and sowing window. Weather conditions during the trials were challenging, with prolonged winter wetness and frost followed by spring drought. These stresses affected both winter and spring crops. Yet they also provided insight into resilience. Winter-sown bean-based mixtures offered strong wholecrop biomass even when grain options were more limited. Spring pea-wheat mixtures showed grain yield resilience despite limited fertiliser inputs.

The table below provides an example of crop species/ variety combinations crop-mixtures which gave best protein yields – even with no nitrogen fertiliser added. It should be noted that these per hectare estimates are extrapolated from plot (10 m2) scale trials.

This suggests that harvest flexibility may become especially important. The option to harvest either as grain or as wholecrop forage may prove highly valuable in the face of increasingly unpredictable weather. If grain fill is compromised by drought, heat or lateseason rain, a wholecrop option may still deliver high protein yield and useful forage value. Wholecrop harvest can also allow earlier field clearance, opening opportunities for timely drilling of the following crop.

As climate change increases weather variability, having this flexibility may be as important as maximising yield in a good year. A system that can switch between grain and wholecrop depending on the season offers a way to manage risk. It also spreads marketing options, from feed grain to forage: or even protein extraction in the future.

This continuity is important, and whether to intercrop is not a one-season question. It requires testing over multiple years and sites to understand interactions between species, varieties, soils and weather. So, despite promising early findings, there is much still to do. One key area is understanding which traits underpin successful intercrop combinations. For example, what canopy structures allow light sharing rather than restriction? Which rooting patterns allow better soil resource use? How do differences in flowering time and maturity affect competition and harvestability? Without clear answers, it is difficult to guide breeding programmes.

Breeding for intercropping requires a systemic shift in focus for breeding, agronomy and downstream value chains. Varieties bred purely for monocrop performance may not be optimal partners. Traits such as reduced height dominance, complementary life-histories, lodging resistance in mixed stands, and predictable maturity could all be important. The strong performance of certain combinations, such as Mantara with Ketu, hints that these traits are important for successful combinations, but they need to be identified and selected deliberately.

There is also a need to develop value chains for wholecrop use. While grain markets are well established, wholecrop legume-cereal mixtures require clear routes into livestock rations, dairy systems or potentially biorefining. If wholecrop options are to act as a resilience tool under unpredictable weather conditions, farmers must have on-farm uses or be confident of a viable market.

In summary, early results show that pea-bean and pulse-cereal intercrops can increase protein yield, reduce reliance on synthetic nitrogen and offer yield-resilience in the face of challenging weather conditions. The benefits are real, but conditional. Stand density, variety choice and harvest strategy are all important. The flexibility to harvest as grain or wholecrop may become increasingly valuable as weather patterns become less predictable. However, to move from promising trials to widespread adoption, further work is needed on traits, breeding, nutrient dynamics and market development. Intercropping offers a practical pathway towards more resilient and home-grown protein systems, and it remains, as most agriculture is, a work in progress, with ‘every day a school day’.

Life cycle assessment for cropped systems

Life cycle assessment (LCA) is a way of measuring the environmental footprint of farming systems, from fertiliser use through to greenhouse gas emissions. While widely used in other industries, it is now being applied to arable farming. Using data from a 14-year field experiment (2009–2023) at the Centre for Sustainable Cropping, researchers assessed the value of growing spring field beans ahead of spring barley. The results showed that barley following beans required around 20% less synthetic nitrogen fertiliser (about 30kg/ha, consistent with RB209 guidance), though further reductions are possible and average yields increase. In addition, environmental impacts were reduced by around 25%, and barley yields increased by an average of 1.2t/ha, except in drought years. This highlights both cost-saving and environmental benefits of including beans as part of a rotation.

The model works by first mapping realistic current crop sequences from national cropping data and then testing alternative rotations that increase pulse crops while keeping major cash crops like wheat largely in place. Early simulations suggest the pulse area could increase to around 18% nationally, with only modest reductions in the wheat and barley area. A full environmental assessment of these scenarios is underway, with results expected later this year.

Addendum – on intercropping versus monocropping

All this said, it should be highlighted that intercropping is not automatically better than growing pulses on their own. In some situations, monocropping, especially with field beans, may still be the stronger option. Field beans commonly produce higher protein yields than peas as they have a higher protein percentage and can deliver more tonnes of protein per hectare. If your main aim is to maximise grain protein yield, and you have reliable harvest conditions and a clear market, a well-managed bean monocrop for grain can be hard to beat. Additionally, monocropping also keeps things simpler. Seed rates, weed control, crop protection and harvest are more straightforward. There’s no need to balance two crops in the same field or worry about competition between them. For many farms with established bean agronomy, this reliability and ease of management are important advantages. That said, intercropping can offer benefits in tougher or more variable seasons. Mixing crops can spread risk, improve resilience and sometimes reduce the need for fertiliser. It may also give the option to harvest as wholecrop if grain fill is poor and grain harvesting perhaps not possible. So, it is not a case of one system replacing the other. The best choice depends on your soils, weather, market options and appetite for risk, or need for risk avoidance.

Acknowledgement statement

The James Hutton Institute receives funding from the Scottish Government’s Rural and Environment Science and Analytical Services (RESAS).

The authors also gratefully acknowledge the support and collaboration of all contributing projects and their partners – including the InnovateUK funded project www.ncsproject.co.uk; a PhD project supported by BBSRC/UKRI – the Sustainable Agriculture Innovation – Collaborative Training Partnership (www.ctp-sai.org) with PGRO and Cranfield University; the EC and Innovate funded Research and Innovation Actions www.econutri-project.eu, and www.legumESproject.eu; plus collaborators including PGRO, HarBro Ltd, NPZ (pulse breeders), and Scoston (organic) Farm, by Dundee).

This work is also progressed in close collaboration with many colleagues, though specific acknowledgement for the expertise and guidance of LCA specialists at the National University of Ireland Galway has been crucial, and specifically from: Prof David Styles, Dr Colm Duffy and Mr Umut Kartal.

Find out more about The James Hutton Institute at www.hutton.ac.uk

Further reading available here