Seven years ago, Cotswold growers Alex and Andrew Bullock embarked on an organic conversion that would call for a complete overhaul of their establishment system.

Losing the ability to clobber weeds from the sprayer seat meant the min-till and no-till regime employed on much of the 1,200ha they farm near Bourton-on-the-Water had to go.

In its place came a return to soil inversion. A pair of seven-furrow Lemken Diamants were drafted in – both fitted with short, slatted bodies to suit the farm’s shallow brash soils – along with an old five-body Dowdeswell to tackle smaller patches.

See also: Herts firm invests in monster 15t, 18m Horsch Avatar drill

Alex Bullock © James Andrews

Their 6m Horsch Avatar then stepped down from front-line duties, leaving a 6m Horsch Sprinter running 1in Bourgault coulters to establish most of the arable area.

Once furrows had been knocked down by a Vaderstad Carrier or Farmet Fantom, this did a decent enough job, though it struggled to lift wheel marks in sticky soils and, despite working quickly, required three separate operations.

“We decided that we could really do with a combi drill, ideally with tines rather than discs so that we wouldn’t get blockages in the wet,” says Alex.

“It would need to be 6m wide to fit in with the rest of our kit and cover the ground at a decent speed, plus we wanted to be able to sow a cash and companion crop at the same time.”

Custom combi drill

Ready-made options were thin on the ground, but after a phone call to Weaving Machinery, the Worcestershire firm agreed to build them something bespoke.

The starting point for the project was a 6m Concept power harrow fitted with a hydraulically adjustable tine toolbar – an outfit that the factory had assembled before.

However, rather than the typical setup of having a sole 2,200-litre tank on the front linkage, they added a second 1,800-litre unit above the harrow.

Another complication was the fact that Alex and Andrew wanted seed from both hoppers to mix and be delivered down the same coulters.

On the one hand, this would make sure the two crops were evenly distributed throughout the field, rather than being in distinct bands.

But it would also make it simpler to use both tanks when planting a single type of seed.

To achieve this, Weaving created a manifold that channelled the contents of the front tank into the air stream of the rear.

This was simple in theory, but having two hydraulic fans pushing air into a single set of pipework created far too much back-pressure.

In answer, designers came up with a venturi exhaust – mounted to the side of the rear hopper – which removes most of the air generated by the front fan before the two streams meet.

Seed from the front hopper joins that from the rear © James Andrews

A venturi exhaust removes air generated by the front fan © James Andrews

Metering is carried out by separate Accord-style electric units front and rear, though they are set up and monitored through the same RDS in-cab screen.

Each is calibrated individually, but the settings can be copied across to save time when using both for the same type of seed.

Wider row spacings

Another requirement was that the drill could quickly switch between planting at the conventional 125mm and wider 250mm row spacings.

The purpose of the latter is to provide enough room for inter-row cultivation – one of the farm’s core techniques for controlling weeds after switching to organic – which is carried out by a pair of Carre camera-guided hoes.

Row spacings can be quickly switched between 125mm and 250mm © James Andrews

This wider banding is achieved by placing rubber bungs in the distribution head and removing every other coulter to prevent wearing them out unnecessarily.

Alex also offsets the drill by half a row in the tractor’s GPS to account for the end coulter on one side being shut off.

One consequence of doing this is that it caused another air pressure increase in the pipework.

But by adding rubber exhausts on the remaining coulters, the system was brought into balance.

Heavy operator

The combination of a 6m harrow, hopper, coulters and a double following harrow means the rear assembly is a weighty piece of kit – about 4.6t before any seed is added.

To prevent it being too wayward on the road, Weaving manufactured a removable transport wheel that slots in the centre of the rig.

Fitting this is a slight performance, as the drill has to be reversed over it before it’s locked in place. However, a carefully positioned camera makes it relatively easy to line up.

A drill of this stature requires the services of a substantial tractor.

In the Bullocks’ case this is a 400hp Massey Ferguson 8740 Dyna VT, running 900mm-wide tyres at the rear and 750s at the front.

It has ample power and lift capacity for the job, plenty of oil flow to run the two hydraulic fans and weighs a suitably hefty 11t.

Nevertheless, it can be a little light on the front end when the 910kg hopper is nearing empty.

Redesigned harrow brackets keep weight closer to the tractor © James Andrews

Weaving did manage to improve this by altering the power harrow brackets to bring them a couple of inches closer to the back of the tractor, though it’s still not perfect.

“I’m amazed how much difference it made for such a small adjustment, but I could do with a couple of extra weights at times,” says Alex.

Using it

To achieve a decent seed-bed when working directly onto furrows, Alex travels at 7-8kph.

It’s slow compared to the 14-15kph of the Sprinter, which still does a fair chunk of the acreage when conditions are good.

But because the min-till drill requires two rather than three passes, the combi isn’t any more expensive.

“I’ve done a few calculations and there’s not much in it – plus we aren’t tying up another tractor and driver.”

The outfit is versatile, too. To make it more agile when working in small fields and on Sustainable farming Incentive (SFI) plots, the rear drill can be used without the front tank.

That said, a 2t weight is required to keep the tractor’s front wheels grounded.

The combi gets used to establish virtually all crop types in the farm’s organic rotation, which starts with winter wheat and is followed by spring oats and spring barley.

On farms with livestock, the latter crop is then undersown with a clover ley using a 12m grass harrow fitted with an Einbock seeder.

For those with arable only, this is substituted with one of two SFI mixes: NUM3 legume fallow or AHL1 pollen and nectar.

Spring crops are also preceded by cover crops which are, as of this year, put in by the 6m Vaderstad Carrier running Crosscutter-style discs purchased from APM.

Weaving rigged this up with a distribution head and pipework to a series of spreader bars positioned between the discs and packer.

These are fed from the same front tank used on the combi drill, helping make good use of an asset that would otherwise be parked in the shed.

The total cost of the seeding conversion was £3,500, with a set of 50 discs costing about £1,350