Better crop genetics and the use of intercropping could improve the success of growing legumes in parts of the UK, helping fulfil demand for high protein livestock feed. Abby Kellett reports.
Despite growing demand from UK livestock producers for locally-sourced protein feedstock, about 60 per cent of protein crops used for animal feed are imported, largely because of the difficulty in growing consistently high yielding legumes in some parts of the UK, according to Dr Robin Walker, a researcher at Scotland’s Rural College.
Of the 2.6 million tonnes of protein-based animal feed used annually in the UK, about 37 per cent derives from home-grown cereals and 3 per cent from home-grown pulses. The remainder comes from imported maize (5 per cent) and soya (55 per cent), according to 2016 Defra figures.
With a current value of £375 per tonne plus transport costs, importing soya can be expensive, but its high crude protein content of about 45 per cent makes it a valued feed component for many farmers.
But should the UK not be looking to better fulfil its own protein demand? David Rhodes, technical manager for DLF Seeds says: “Imported soyameal still holds a monopoly as the highest protein content feed, but it is expensive, and new plant breeding techniques mean home-grown legumes can now really hold their own.
They have been specially bred to be high in protein and valuable minerals, while also being easier to grow than their predecessors through improved vigour and disease resistance. As legumes, they will also contribute to soil nitrogen for the following crop.
“Being able to grow protein yourself also increases farm self-sufficiency and provides some protection from fluctuating market prices for protein substitutes.”
According to Dr Walker, the main barrier to increasing the production of home-grown proteins is the inconsistent yield and quality which is associated with many legumes, particularly in northern England and Scotland where demand for livestock feed is high.
“Peas and beans are the main protein crops grown in northern England and Scotland, but some farmers are put off growing these crops because of the difficulty in getting them established in cold soils. They can also suffer badly from frost damage, they are vulnerable to lodging and can be difficult to harvest.”
He believes intercropping could be a potential solution.“SRUC trial work from the 2016 and 2017 seasons showed how intercropping cereals with grain legumes in spring can lead to more reliable production of high protein feed, particularly in north of the UK.”
As part of the trial which took place in Aberdeenshire, the following intercrops were sown and compared to legume monocrops:
In most cases, the presence of the cereal boosted the yield of the legume and vice versa. In some cases the effect was quite dramatic.
Dr Walker says: “In year two of the experiment, our plot of just peas failed completely. But where the peas were grown alongside Westminster barley, they produced about 1.2t/hectare of dry matter and the barley produced about 1.6t/ha of dry matter.”
Similarly, the lupins failed to establish when grown independently, but established successfully when grown alongside barley. The only instance when intercropping had a negative effect was when the beans were grown with barley.
“This was a result of barley shedding its seed,” says Dr Walker.
“In most cases, the higher yield of the legume associated with intercropping led to a higher nitrogen output per hectare than legumes which were grown on their own, although there were some exceptions when the cereal overwhelmed the legume.”
Although it is not entirely clear how the presence of the cereals led to improved legume performance, researchers suspect the cereals helped prevent the spread of disease between legumes and, in some cases, prevented the legume crop from lodging.
The research team also sowed four different varieties of soya to assess the potential of growing the crop in northern regions of the UK, but both years the soya failed to establish.
“After it failed the first year, we grew it with a fleece the second year but it did not make any difference. There is still a long way to go before we have a variety which is compatible with cold northerly weather,” says Dr Walker.
As part of the Innovative Farmers Group, 12 farmers in the South West are investigating the potential for commercial production of combinable organic protein crops, lupins and soya.
The Mole Valley Farmers group have completed a first year of trials, growing one white variety and one blue variety of lupin, and their results are set to shape a further year of research.
Lupins have a reputation for being difficult to grow in the UK, but with rising demand for organic proteins for animal feed making sourcing increasingly difficult, and with new seed varieties entering the market which may increase the possibility of success in growing locally, the group were keen to see whether they could make it work on their land.
While the white variety largely failed, the blue showed promise despite the challenges of an unpredictably dry April which reduced establishment last season. Each of the participants used one or both lupin varieties alongside a range of weed control measures, with mechanical weed control proving the most successful. Some chose to intercrop with vetch but this tended to result in excessive competition.
Mole Valley Farmers organic feed specialist Nigel Mapstone, who is coordinating the trials, says: “We have gathered some good insights which have encouraged us to implement the next trial on larger plot sizes, with denser planting and no intercropping, which should improve establishment and harvest success.”
Discussing their second trial, the group are considering using two blue varieties, Regent and Iris. These have different growth habits and the group is keen to see whether this results in significant differences in yield, quality and weed competition.
Growers should also consider the use of forage legumes to increase the protein content of silage or grass leys.
Mr Rhodes says: “With clovers, the main options are white and red clover depending on the growing conditions. Both are highly digestible and productive, producing a sward with 17-19 per cent protein.
“White clover has good persistence and is the natural choice in mixes for grazing due to its small leaves, lateral growth habit and tolerance to close cropping.
“Red clover is better suited for cutting and ensiling due to its aggressive upright growth. Under dry conditions it performs extremely well as it has a prolific rooting system.”
Lucerne is another option worth considering as newer varieties are more reliable and efficient.
“Most alfalfa varieties contain 18-20 per cent protein, compared with 14 per cent for grasses and 9 per cent for maize. It can also be grown with grass, which can produce an optimal energy-to-protein ratio. Having a deep rooting system means it has a stable yield even in periods of drought.
“Breeders are working continually to improve yield, protein content, disease-tolerance, persistency and digestibility of legumes, and to develop varieties for all soil types and climate,” he adds.