Modern sprayers can be sophisticated machines and offer their operators a high degree of comfort. But few, it seems, can compare with what the Mercedes-Benz Unimog can provide. Andy Collings reports

Costing more than £150,000 two years ago, the self-propelled sprayer operated by Nottinghamshire farming and contracting company Farmeco is certainly not cheap. But managing director Keith Challen reckons it is the Rolls-Royce of self-propelled sprayers and offers operator comfort and technical features on a level few machines can equal.

The Rolls-Royce is actually a Mercedes, with the sprayer based on a forward-control Unimog U 400.

“I wanted a sprayer that above all else, was easy and comfortable to use,” he says. “We have about 4500 acres of combinable crops to look after and, bearing in mind we apply liquid fertiliser, the sprayer needs to make about 10 passes during the growing season – a total of 45,000 acres.”

This acreage is split between several contract-farmed areas, some of which are over 20 miles apart.

“Due to the high distances involved I also required a sprayer that could be driven safely on the road at a useful speed,” he says. “And that meant having a machine with a mechanical gearbox and good brakes.”

He concluded that the forward-control MB Unimog ticked all the boxes and set about arranging for South Cave Tractors, which carries out Unimog’s conversions, to produce a 4000 litre machine with 36m booms.

The machine, which was to replace two 4000 litre self-propelled sprayers, arrived in the autumn of 2006. Shod on 600/65 34 tyres it was specified with an on-the-move tyre pressure inflation/deflation system so that road pressure could typically be set at 2.2 bar and field pressure at 0.9 bar.

The onboard compressor is also used to provide an air-activated dual circuit disc brake system complete with ABS, while independent coil suspension and dampers are positioned at each corner of the rigid chassis to provide a smooth ride.

Power is provided by a six-cylinder, Mercedes engine rated at 231hp which is fitted with an exhaust braking system that avoids heavy, excessive use of the disc brakes. There is no dipstick for engine oil level – the level is monitored electronically and displayed car-style on the in-cab console.

For the transmission, an 8 x 6 box also includes a torque converter which not only allows clutchless changes using an electro-pneumatic shift system but also enables smooth starts simply by increasing engine speed. Cruise control is included in the transmission and top speed is a heady 64kph.

“It’s just an amazing vehicle to drive,” says Mr Challen. “There’s plenty of power and the transmission is a joy to work with.”

The Chafer-built sprayer – a Mid-Tech Legacy 6000 – is pretty sophisticated too, with an advanced computer controlled spraying system.

“We also have a GPS guidance system that allows us to spray accurately, which is particularly useful when spraying oilseed rape that has been broadcast and so has no tramlines,” he says. “We also have individual control of each metre of the boom so that, by using GPS and the automated auto-shut-off system, the boom can be progressively shut down as it runs up to an angled headland.”

“We usually spray pesticide at about 18kph and up to 24kph when applying fertiliser,” he explains. “For slug pellet application there are twin Stocks units attached to the front of the machine.”

The stainless steel 4000 litre tank is filled using two hydraulically driven pumps positioned at the rear of the machine to reduce pipe work. Filling takes less than three minutes to complete.

For the booms, ultrasound-activated height control maintains the required distance from the crop. And a camera screen shows what’s going on at the back of the sprayer.

Mercedes-Benz Unimog forward conversion

• Engine: Mercedes 6-cylinder, 231hp
• Transmission: 8×6, torque converter, 64kph
• Suspension: coil springs and shock absorbers
• Sprayer:
• 4000 litre tank
• 500 litre rinse
• 50 litre hand wash
• Twin hydraulic pumps
• 36m booms, ultrasound height control
• GPS guidance
• Auto boom shut off and start