Setting up cultivation equipment to work soil less deeply could help growers combat blackgrass more effectively on fields where control has been good this season.

Avoiding disturbing previously buried blackgrass seed with cultivations this autumn where seed return from this year’s crop is relatively low will help growers in dealing with the weed, Dick Neale, technical manager of Hutchinsons, believes.

“By not disturbing buried seed, you will have a rough idea of what will germinate, know its resistance status, or at least what chemicals work effectively, and know you won’t be dealing with seed coming back at you from previous seasons.”

But many of the bigger pieces of cultivation equipment are set to work too deeply, he says. “If you’re deep cultivating down to 23-25cm (9-10in) of soil, you’re mixing the soil around and can’t be sure of what will come at you.”

Instead, growers should be aiming to cultivate only the top 10cm (4in) to avoid bringing up blackgrass and other weed seeds.

The potential difference in blackgrass control was graphically shown at Hutchinsons’ blackgrass trials centre at Andrew and Richard Rampley’s farm at Brampton, near Huntingdon.

Part of one field was deep cultivated to a depth of 25cm (10in) using the farm’s usual Discordon settings, while for the other block, the machine was set to cultivate to a depth of 10cm (4in).

“We could do that because it was an older machine with relatively worn discs and legs,” Mr Neale says.

Both blocks were sprayed off with glyphosate pre-drilling and then treated with a pre-emergence treatment of Crystal (flufenacet + pendimethalin) at 4 litres/ha plus 100g/ha diflufenican.

But the block that had been shallow cultivated didn’t require a follow-up spray for Atlantis or broad-leaved weeds, which the deeper cultivated block did.

Not only did that contribute to a total saving of £75/ha when combined with the establishment cost savings, but it also allowed a 40% higher work rate and a better soil structure, which benefited the wheat crop during the spring drought.

“To make a good seed-bed, you just want to work in the upper zone of friable soil,” Mr Neale says. “If you stick in that zone, you don’t do any damage when cultivating.”

But on that field, and many others, cultivating deeper penetrates the clay zone, smearing it a little. “The crop’s roots have then grown laterally along the smear layer in the autumn, looking for a way down. It creates a disconnect.”

In contrast, the roots in the shallow cultivated block had spent an extra two months growing deeper, which had helped the crop cope better with the spring drought.

Shallower cultivations should be possible with most commonly-used equipment, Mr Neale reckons. “A lot of growers don’t change the settings from those set in the factory, but you should be able to get as shallow as six inches with most machines.”

But he is also aiming to encourage machinery manufacturers to design more readily applicable machines. “The vast majority of machinery is engineered for the deepest level of cultivation that may be needed, which means that tine design is often too aggressive when shallow working would be more appropriate,” explains Mr Neale.

“I would hope we can encourage better leg/tine design that allows quick change options within the same machine base frame. Shallow working machines are often designed to be lighter overall, but in stiff clay you still need the physical bulk of a heavy frame to maintain stability in the soil and provide sufficient consolidation with the final press element.”

Direct drilling oilseed rape could make blackgrass control easier than where a sub-cast system has been used, Hutchinsons’ trials suggest.

The firm has compared blackgrass control in oilseed rape established using a Horsch C04 tine direct drill and a Cousins V-form subsoiler with a seed-box placing seed behind the subsoiler legs.

Both established the crop effectively, but where the Horsch drill was used, blackgrass control was around 10% higher, Mr Neale says.

That might be because the crop is not only more vigorous in the sub-cast system, but also in the blackgrass, he suggests. “You have a more open, fractured soil, so the blackgrass grows quicker. It was around four to five leaves when treated with propyzamide in the sub-cast oilseed rape, compared with three leaves in the Horsch system.”

Sub-cast rape could also open up greater potential for propyzamide to reach water, Dr Ellerton suggests. “If you go too deep it could provide a route.”

DEFRA research suggests that fissures created within the soil don’t close up, Mr Neale explains. “That could explain why we see spikes of propyzamide in water when there hasn’t been any drains flowing.”

One solution could be for a shallower leg design for the subsoiler, he says. “Most are designed to work deeper. Again, we are talking to manufacturers about designing kit to do the job.”