Growers considering a shift away from the “subcast” technique of establishing oilseed rape to improve the performance and economic viability of their crops are being offered an upgrade that enables this without a wholesale change of implement.

Replacing dribble pipes with soil-engaging coulters will provide the more consistent seed depth that a drill provides, say manufacturers, without losing the attractions of sowing with a subsoiler.

“This is the next step in the evolution of what we call till-seeding – sowing into stubble in line with the subsoiler legs,” says James Woolway of Opico. “Till-seeding leads to better overall crop establishment, improved root structure, stronger plants and growth and ultimately better yields.”

See also: How to grow oilseed rape without neonicotinoids

“But while crop establishment is already very good, drilling at a consistent depth gives even better results – it is the key to improving germination and evenness of plant size,” he says.

“Subcast” oilseed rape establishment has proven attractions, not least the deep soil restructuring that is acknowledged as being essential to enable plants to put down deep roots for a firm anchorage and a productive search for moisture during the growing season.

Another attraction is the relatively low cost of mounting a seed hopper, metering system and distribution pipes to extend the role of an existing or newly purchased subsoiler, alongside the ability to get crops established in a single pass.

But while growers have undoubtedly experienced good results with this approach, outcomes are not always consistent and at a time of low returns, the crops needs the most effective, but least-cost, establishment.

For some, sowing off the back of a combination cultivator is a better bet because of the improvement in seed-bed conditions this approach provides. Others prefer to go the whole hog and use a seed drill – ideally, with soil-loosening tines incorporated somewhere along the line to get that all-important restructuring down below.

Coulter arms and tines for the Rehab seeder come from the Pro-Til seed drill.

Implement manufacturers now offering seed coulter kits reckon this upgrade offers the best of both worlds – the benefits of a seed drill and subsoiler in one implement, with no energy wasted or weeds encouraged to germinate by cultivating the entire surface.

“Farmers have tried many ways of reducing the time and cost of oilseed rape establishment, but too many have struggled to achieve consistent yields in all soils and conditions,” says Martin Lole of Mzuri. “Systems that trickle seed down behind subsoiler legs work well in some conditions, but disappoint in others.

“There is always the risk associated with uneven sowing depth and inconsistent germination,” he adds. “Many of the growers who used our Rehab Seeder for the first time last autumn report crops came into flower a couple of weeks earlier than those sown using other methods.”

Ensuring treated seed is placed firmly below the surface by drilling rather than dribbling is another factor in favour of this approach, suggests tillage implement maker Philip Watkins, who offers a disc coulter kit to fit any subsoiler – or cultivator, for that matter.

It comprises mounting brackets for a flexible tine-covering harrow and a coulter bar, both of which are mounted on separate parallel linkage.

Twin-disc openers are used for placing seed and these are pivot-mounted to the toolbar with coil springs allowing controlled movement over stones and contours. Plastic depth-control wheels that also consolidate the seed row are set using a pin-and-hole arrangement.

The seed coulter kit developed by Dal-Bo to fit the T-ring roller on the back of its Ratoon shear-bolt and auto-reset subsoilers also has twin-disc openers followed by adjustable press and depth control wheels mounted on Y-forks to firm soil along the seed row.

Spring tension on the Dal Bo Ratoon’s coulters is adjustable centrally; sowing depth is adjusted individually using a pin and hole mechanism on the press wheel.

The press wheels are individually adjustable using a pin-and-hole quadrant, but coulter tension spring pressure is adjusted simultaneously across all coulter arms using a central turnbuckle.

There are six- and 12-row versions, with splitters for the main delivery tubes on the larger version delivering seed from an Einbock (or similar) hopper and metering unit. Seed rate is regulated using an in-cab controller linked to a land-driven metering wheel or radar.

A 3m version is priced at £8,070 and fitting kits are available to suit subsoilers of other makes with different frame dimensions.

The He-Va Accu Disc seeding system from Opico is available with single- or twin-disc openers to suit different soils, with each assembly carried on a short spring-tensioned parallel linkage positioned in-line with the soil-loosening tines.

Coulter seeding system from Opico for He-Va and other subsoilers is designed to place not sprinkle seed for more even sowing depth and germination.

Coulter pressure is provided by a spring and adjusted individually to suit different soils and conditions on the day using a push-pull mechanism. Depth adjustment is handled separately using a turnbuckle, which is located at the left-hand side of the implement for easy access with a scale for guidance.

Each single- or twin-disc assembly is followed by a rubber press wheel carried on a single arm to minimise the risk of becoming gummed up with sticky soil as it closes and consolidates the seed slot.

The Accu Disc system is available on 3m (five-leg) He-Va subsoilers for £3,564 single-disc and £6,130 twin-disc, and on the 3.5m rigid, 4.4m and 5m folding, and 5m and 6m (11-leg) trailed He-Va subsoilers priced £7,412 and £13,163 for the widest implement. Fitting kits for 3m and 3.5m subsoilers of other makes cost £492.

Sumo has gone for a simple coulter assembly in proposing a sowing option for the Trio cultivator, which combines deep tines, discs and a packer in one implement.

The Single Disc Opener is available as an alternative to the pre-packer seed broadcasting system, which also uses the Sumoseeder package employing the firm’s simple Orga metering mechanism and seed distribution head.

The Sumo Single Disc Opener is attached to the Trio frame by a rubber-cushioned horizontal pivot, with pin-and-hole adjustment provided for sowing depth and coulter pressure.

“The single disc openers are the same as on our new DD direct drill,” says Sumo drill specialist Marcus Ainsley. “On the drill they are carried on parallel linkage, but for this application we wanted to keep things as simple as possible.”

Pin-and-hole adjusters separately set the working depth and up to 80kg of downward pressure on the single notched disc, and although each 50kg assembly is clamped rigidly to the 100mm box section frame of the Trio, a horizontal pivot provides rubber-cushioned movement.

Each of the 450mm hardened steel discs is set at 5deg, with a slimline tungsten-edged opener placing seed and the large traction tread tyre consolidating the row for good soil-to-seed contact.

They are priced at £485/unit.

The Rehab Seeder from Mzuri differs from the other subsoiler seeding systems in using tine rather than disc coulters.

In fact, the trailing arm coulter assemblies, which are held in place by three hitching pins for quick attachment and removal, are the same as those fitted to the company’s Pro-Til strip-tillage drills – as are the low-draft soil-loosening tines of the Rehab itself.

The Mzuri Rehab Seeder is alone in deploying tine band coulters behind the soil loosening legs.

“Our aim in designing the Rehab Seeder was to remove the inconsistency of sowing depth and germination experienced with seed trickling system,” says Mr Lole. “Seed is always placed in a well-cultivated tilth that is consolidating immediately to achieve effective soil-to-seed contact and with restructured soil in the root zone directly below.”

The Rehab is equipped with a leading disc to cut through stubble and laid trash ahead of each cultivating leg, which is shaped to lift and restructure the soil without excessive disturbance at the surface.

Individual press wheels, rather than a full-width packer, consolidate the resulting tilth while leaving the soil between untouched, then winged coulters place seed in wide bands at 600mm centres.

Hydraulic cylinders connected across the implement provide coulter pressure, with enclosed springs maintaining pressure on the covering press wheel; a new convex-shaped press wheel is said to have given good results by further improving soil-to-soil contact.

The Seeder unit for the 3m, five-leg Rehab is priced at £13,549 complete.