Brian Henderson's Arable Matters: Will ARIOB set our pulses racing?

The spiralling costs of bagged fertilisers and the search for more carbon efficient methods of supplying crops with nutrients – along with the race to reduce the livestock sector’s reliance on imported soya – have all led to a renewed interest in the role which domestically grown field beans and other legume crops can play in fixing nitrogen.

But while we’ve all been assuming that beans and other legumes are capable of fixing a significant amount of nitrogen – both for the bean crop itself, for anything grown along with it and also for the following crop – until the James Hutton Institute got round to organising this piece of country-wide research, there were no real hard figures available from field scale measurements.

So, it was probably about time that someone got round to measuring the benefits which can be reaped from harnessing the symbiosis between legume crops and soil bacteria which not only facilitates the harnessing of naturally occurring atmospheric nitrogen while reducing the need for added – and very expensive – inorganic 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,” said Prof Euan James, a research leader at the Institute’s Ecological Sciences department and co-author of the study.

The study looked at the levels of nitrogen fixation in a range of different farm types across the country using a range of production systems in fields stretching from Orkney all the way to the South of England – and was backed up with intensive field-scale investigations the JHI’s Centre for Sustainable Cropping (CSC) at Bulruddery Farm, on the outskirts of Dundee.

“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,” said Professor James.

“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.”

And agroecologist and legume specialist with the Hutton, Dr Pete Iannetta, who also authored the report 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.”

He said that access to long-term whole-system datasets of the CSC, which was set up in 2009 to design an integrated cropping system for multiple benefits and test the long-term impacts on biodiversity and whole-system sustainability and is managed by Dr Cathy Hawes, had played an important role in verifying the findings:

“There is nothing like it globally for agroecological studies of arable cropping,” said Dr Iannetta. “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.”

I asked Pete how much of the nitrogen which was fixed would be available to the next crop – which is probably of as much interest to farmers as how much goes into the bean crop itself.

I suspect that few will be surprised to hear that there’s no definitive answer on this one, as it depends not only on how successful the bean crop had been in establishing and growing in the year of harvest but also on the weather conditions over the winter following the harvest as this has a substantial effect on the level of leaching and mineralisation.

A ballpark estimate, however, put the range as high as 100kg/ha where the crop had been strong and little had been leached over winter, down to around 25 kg/ha where a poorer crop had been followed by a wetter winter.

Needless to say the topic of the weather and the boom-bust cycle of growing beans in Scotland which has been scarred into the memories of many who have grown these pulses in the past, was also discussed when I was speaking to him.

For the lateness of ripening of most bean varieties sees them pushed well into the unpredictable harvest zone in Scotland, where this crop can sometimes hang on until literally months after the rest of the harvest is finished.

I guess it’s because there’s no real breeding programme aimed at producing varieties for Scotland’s maritime climate – but the researcher said that the institute assessed varieties for their suitability. He added that seed from a ‘Scottish bean’ – which has both early maturing and dwarf characteristics – and which had been donated to the Institute by an individual who had been working in the field for some time, was currently being multiplied up for further assessment and possible national listing.

So it might be a case of watch this space …

With hopes running high that there will be some revelation on future policy direction from the Scottish Government’s deliberations through the Agriculture Reform Implementation Oversight Board (ARIOB) at NFU Scotland’s agm which is underway, it’ll be interesting to see if the push for growing more nitrogen fixing crops is taken forward as part of this policy. In the process, will it fire the starting gun which could set our pulses racing?

Because increasing the domestic production of crops, such as peas and beans, was certainly recognised as an area of interest by the arable farmer led group – but in the short term at least it was also recognised that there were a few draw-backs on top of our already temperamental climate.

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The lack of any development on the marketing side was certainly one issue – with feed compounders certainly being far keener in the past to continue importing commodity-grade soya than to build the less reliable quantity and quality of domestically produced beans into the formulation of their rations.

On the commercial front, there was some resistance to such a move from the vining pea and bean sector which, quite sensibly, likes to have a reasonable supply of ground available which has been free from other pea and bean crops for several years. (And if you consider the trouble facing the seed tattie sector which is facing an existential threat due to the huge increases in eelworm populations which has been brought about by reduced rotational breaks between potato crops in recent years, then maybe they are right to be a bit more far-sighted.)

But some research from last year did highlight that growing peas and beans were amongst the most effective measures for reducing greenhouse gas (GHG) emissions on farm.

Scientists at Scotland’s Rural College (SRUC) assessed various farm technologies and practices aimed at reducing GHG emissions as part of the Scottish Government’s plans to meet a net-zero target by 2045.

However, while the researchers found that increased grain legume cultivation was one of the most effective measures at cutting GHG emissions – providing an estimated average annual reduction of 553 kg CO2e (carbon dioxide equivalent) per ha – it was also the most expensive option, with a net average cost of £406 per ha per year.

So, although the desire to save on fertiliser bills while saving the planet might be enough to set our pulses racing, I guess only time will tell if such notions will ever amount to a hill of beans …