Bringing early-drilled first wheats back into a heavy land rotation without compromising the progress made with blackgrass control has been the focus of work carried out at Agrovista’s Project Lamport site this year.

After nine years looking at different cultivation, cover crop and following crop combinations, latest results from the heavy land, high blackgrass site in Northamptonshire suggest that growing two first wheats in six years is possible with an integrated approach.

Providing establishment techniques are based on shallow or minimal soil movement to keep blackgrass levels manageable, a rotation where winter wheats are interspersed with spring and cover crop combinations is working well at the site.

“A good rotation which includes spring and cover crops and has a focus on soil health will allow September drilling of winter wheat for maximum profit, even where blackgrass has been challenging,” says Agrovista’s Niall Atkinson.

See also: Why BYDV-tolerant barley may prove itself in disease hotspots

A full herbicide programme still has to be applied to the wheat, he acknowledges, but the key is the use of cultural control methods throughout the rotation and the timely destruction of cover crops.

Broadcasting cover crops into the previous year’s standing crop in June or July before following it with a spring crop has been successful, he reports, with the covers working as trap crops and getting blackgrass to grow, as well as helping with water infiltration.

“Broadcasting the cover saves time and money, minimises soil disturbance and still gives good establishment,” he says. “The lesson has been that the sooner we can get the cover crop growing here, the better.”

However, broadcasting success is affected by previous chemistry use, especially diflufenican, he warns, so herbicide use must be planned with this approach.

The best spring crop yields came from desiccating the cover crop around Christmas time, he reports. “On this site, a late destruction date doesn’t work – it just results in soil moisture being held too close to the soil surface, creating difficulties with establishment.”

A problem that can arise with a Christmas cover crop destruction date is a wet February period, which then causes the high silt content soils to slump, he acknowledges.

“For that reason, we are going to look at differential destruction timings, taking out some species, but leaving others for their soil conditioning abilities.”

Using the two-year legume mix AB15 in the rotation instead of a cover crop/spring crop combination hasn’t been successful due to the high weed pressure, he reveals.

“We had to mow it between five and six times last year to prevent blackgrass from taking over, which when you add to its seed costs, doesn’t stack up. We can do more profitable things here.”

Where there isn’t the grassweed pressure, AB15 can be a good entry for winter wheat, he accepts.

Strategic soil loosening

© Agrovista

Strategic soil loosening has a place and can work well with cover crop roots to relieve compacted soils, allowing the following crop to be established with less disturbance, says independent soils expert Philip Wright.

Releasing cover crop roots will allow them to grow through a compacted layer, so any loosening should take place to a depth just below where the roots have halted, he advises.

“The ideal is to get soil biology to do the soil structuring, but it needs oxygen for that to happen,” he says. “These Lamport soils don’t self-structure very well, so the appropriate use of some metal can help.”

Putting in a cover crop will always improve the situation, stresses Mr Wright, so that should be a priority if stretching the soils isn’t an option or workloads won’t allow it. “With really severe compaction it’s best to stretch the soil and put the cover crop in at the same time, as you will need the combined effect.”