Part article taken from Crop Production Magazine
Two years of trials undertaken by Agrovista have shown cover crops followed by a spring wheat delivers by far the lowest population of blackgrass. The Project Lamport heavy-land site in Northants was taken on by the company in 2013. The set of trials, sponsored by Bayer CropScience, pitches 12 different regimes against each other over five years on a very high population, highly resistant blackgrass site.
“In the first year, we achieved a blackgrass population of less than two heads/m2 and a yield off the spring wheat (KWS Willow) after cover crops of 8.6t/ha,” reports Stewart Woodhead of Agrovista.
“In the second year, each plot followed the same regime as the first. While the blackgrass population in the winter wheat plot grew by five times, where the cover crop had been planted, just four heads/m2 were counted in the following spring wheat. It outperformed even the plot that was fallow in year 1, followed by winter wheat in year 2 that had a population of 36 heads/m2,” he adds.
The secret to achieving such a low population is the right cover crop seed mix and agronomy in front of the spring wheat, he says.
Agrovista approaches spring cropping from a different direction. If you have blackgrass and you’re on heavy land, the type of cover crop you choose is key.
“You’re aiming to maximise moisture extraction so you can make a good seedbed in the early spring. Specific spatial establishment of the crop is also important – you’re not smothering the blackgrass, but want to encourage it to grow.”
The mix should help the soil structure to allow direct drilling of the spring crop and so minimise soil disturbance that would encourage blackgrass. “The carbon nitrogen ratio is also important – you want a cover crop that breaks down easily so it doesn’t lock up N from the following crop.” The best cover crop mixes, he maintains, are those that combine black oats (Avena Strigosa) with common vetch or berseem clover. “But choose a late variety of black oat, such as Cadence or Panache – early varieties can set seed.” The legumes have different rooting habits, continues Stewart Woodhead. “Vetch roots more horizontally, aiding surface structure. But berseem clover cover crops can’t be counted towards your ecological focus area (EFA).”
The cover crop should be established as a crop from mid Aug to early Sept. “Drilling depth wants to be 25-35mm – you want the crop to establish ahead of the blackgrass, so not too deep. The seed rate depends on drilling date and fertility of the soil,”
The result is better than a stale seedbed for germinating blackgrass, he maintains. “With a stale seedbed, it’s dry on top and wet below the surface, but the cover crop keeps it moist on the surface, encouraging germination and drier below. There’s better water filtration beneath the surface, which encourages root growth.”
Cover destruction should take place well before the spring crop is established, but the residue should be left on the surface. “Drilling requires a change of mind set – it’s best to drill direct straight into the residue, causing as little surface disturbance as possible. It’ll look scruffy, but there’ll be better soil structure to help the drilling and you’ll get a better result, both in terms of blackgrass reduction and yield.”