Finger on the pulse: The truth about peas, beans and other legumes

We’ve teamed up with the Processors and Growers Research Organisation (PGRO) to answer some common pulse-related questions posted to the AHDB Letterbox. Henny Lowth presents the results.

We receive many questions through the AHDB Letterbox, including those about pulses.

Although we focus on cereals and oilseeds crops, we always consider the wider system, including the role other crops play in the arable rotation.

Many other organisations, including PGRO, provide excellent technical information on pulses in cereal rotations.

We’ve used this information to answer some key questions and provide links to useful resources.

Yes. Several years ago, the Green Pig project demonstrated how faba beans can significantly replace soya in pig diets.

The Nitrogen Efficient Plants for Climate Smart Arable Cropping Systems (NCS) project is building on the work to demonstrate how faba beans can help displace large amounts of imported soya bean meal in UK livestock rations.

Pulses have a favourable environmental profile, compared with many other major rotational crops.

For example, they:

• Fix nitrogen and improve soil fertility for following crops
• Have strong potential to reduce greenhouse gas (GHG) emissions from the UK agricultural sector
• Provide benefits to pollinators, insects and birds (this has been shown in many studies on beans and peas)

The production and use of artificial nitrogen fertiliser is one of the greatest sources of GHG emissions in UK agriculture.

As pulse crops don’t need artificial nitrogen fertiliser, they have relatively low GHG emissions, although the impact is yet to be precisely quantified.

Understanding emissions is another key aim of the NCS project.

There is ample evidence that pulses leave a positive legacy for following crops, including boosted levels of soil nutrients.

In fact, there is compelling evidence for consistently increased yields in crops that follow pulses.

For more information on optimising bean nutrition, visit the ANSWERS project web page.

Plant breeding is driven by private breeders and is beyond the remit of PGRO.

However, PGRO publishes an annual Pulse Descriptive List (DL) for pea and bean varieties.

Until the 2021 edition, it was a Recommended List (RL).

Although evaluation protocols stayed the same, the DL no longer excludes varieties based on performance.

The change allowed the DL to include more information and remove some barriers to innovation in the breeding pipeline, including to help develop novel traits.

PGRO is also a partner in the Defra-funded Pulse Crop Genetic Improvement Network (PCGIN), which develops novel traits.

Just like cereals and oilseeds, harvest dates are ultimately governed by weather and agronomy.

Crops that remain green for longer generally yield better.

There are already early maturing winter bean varieties in Scotland, such as Tundra, Vespa and Vincent.

Early maturing varieties have consistently shown up to two weeks earlier harvest-readiness and have gained traction north of the main bean production areas in England.

The Pulse DL includes maturity-rating data for pea and bean varieties.

There are also interesting Innovative Farmers Scottish bean variety trials investigating this topic.

AHDB recently worked with the UK Agri-Tech Centre to publish detailed guidance on intercropping pulses.

The LEGUMINOSE project also provides details about farmer-led research into legume-cereal intercropping, including information on UK-based trials.

Since 2018, PGRO has also investigated intercropping and often publishes the findings in spring editions of The Pulse Magazine.

At present, there is no guidance on the best variety combinations for intercropping.

It is a vast topic with many variables, including a high turnover of varieties, which makes it challenging to produce robust recommendations.

While beans and peas improve soil health between cash crops, they are not necessarily more or less sustainable than a cover crop alternative.

However, beans and peas often feature in cover crop mixes, with species mixes designed to be greater than the sum or their parts.

The Cover Crops Guide species selection page provides excellent information about the merits of specific species, including legumes.

Well-designed mixes can also mitigate disease risks within the rotations.

Since 2016, PGRO has studied the impact on diseases and pests when using legumes in catch and cover crops, including use in fallow cropping programmes.

It's recommended to leave at least five years between pulse crops to reduce rotational risks, such as from soilborne diseases.