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Winter wheat can deliver decent profits – despite a high blackgrass seed burden, according to one of the country’s leading arable trial sites.

Agrovista’s Lamport AgX site in Northamptonshire is examining how rotations, cover cropping and regenerative agriculture principles can interact to improve soil health and yields while maintaining blackgrass levels at manageable levels.

Over the years, Agrovista has refined an autumn cover crop and spring cereal rotation to keep blackgrass under control. It is a tough testing ground, situated on heavy, high calcium soils that are difficult to manage, with a background blackgrass population of 2000 plants per square metre.

A cover crop, based on black oats, is established in early autumn after a light cultivation to maximise blackgrass establishment, before bulking up to condition and drain heavy soils over winter for spring drilling.

The cover crop and ‘trapped’ black-grass are sprayed off ahead of the spring cereal, which is direct-drilled to minimise soil disturbance and blackgrass emergence.

“The aim is to get lots of blackgrass to germinate in the autumn, and none in the spring,” says technical manager Mark Hemmant. “Everything else bolts on around this.”

While spring cereals have been the cash crop of choice so far, recent work has shown that a return to winter wheat is feasible, but perhaps only one year in three where the resistant blackgrass seed burden remains very high – even after eight years of cultural and chemical controls.

Legume fallow – AB15

One option to help farmers return to winter wheat uses a legume fallow, based on the Countryside Stewardship AB15 option.

The official option was tweaked because it became swamped with blackgrass after being drilled in August – as per the guidelines – and it became puddled in the winter.

Niall Atkinson, consultant and trials coordinator at Lamport AgX, says: “It has done nothing to date for blackgrass control or soil health, and environmentally the mowing stipulated in the scheme has been a bit of a disaster.”

In the alternative option, a black oat and phacelia cover crop was established in August 2018 to trap blackgrass and condition the soil. It was desiccated the following January and again just before the AB15 legume mix was established in the spring.

“The mix grew away very well and we didn’t need to carry out successive mowing to control blackgrass. We sprayed it off in August 2020 and in October established winter wheat with a direct drill to minimise blackgrass germination,” says Mr Atkinson.

“You can see the odd blackgrass plant but control is very acceptable – the wheat looks like a 10-12t/ha crop.” The winter wheat will be followed by a return to the cover crop/spring crop sequence for at least two years.

“A second winter wheat might appear tempting, especially at current wheat prices,” says Mr Hemmant. “But blackgrass explodes. Even after seven years of very low seed return we still haven’t depleted the weed seed bank sufficiently to be able to rely on chemistry.”

The modified AB15 is not allowed under mid-tier rules, being spring drilled, but could be under the Sustainable Farming Incentive. But, if the legume mix still has to be grown for two calendar years, it would have to be followed with a spring crop rather than winter wheat.

A further method tested under extreme conditions could enable growers to return to winter wheat without sacrificing one or two years of cash cropping.

This trial follows a third winter wheat crop that failed in summer 2019 after being overwhelmed by blackgrass, despite a £150/ha herbicide spend.

Half the plot was earmarked for ploughing and half for a cover crop/spring crop sequence. However, heavy autumn rains put paid to ploughing plans, thoughts of a cash crop were abandoned and a cover crop was established the following summer.

In the other half, the cover crop was drilled on 5 September 2019, trapping blackgrass and conditioning the soil. It was desiccated in early January and spring oats were direct-drilled on 27 March 2020 and went on to yield just under 8t/ha.

“We then direct-drilled winter wheat in mid-October when conditions were on the limit,” says Mr Atkinson. “Despite that, two years after a disaster, the wheat looks almost as good as that following our modified AB15.

“And we’ve also had an 8t crop of spring oats in the meantime and have ended up with very little blackgrass. 

“Conventional wisdom says we should have pressed the reset button and ploughed, but this alternative appears to work well.”

Regenerative principles

A further study at Lamport is assessing the prospects of reducing reliance on conventional agrochemicals. A plot of spring wheat was sown in late March, along with sweet allyssum to encourage beneficials and berseem clover to condition soil and fix nitrogen.

“We’ve basically taken away conventional chemical inputs,” says Mr Hemmant.

“This approach seems to have worked well. It’s a really interesting concept. If we can adopt areas of regenerative farming within a conventional system to make it more sustainable, that has to be good.”