15 September 2000


Setting a potato harvester

up correctly is essential to

reduce the risk of tuber

damage and crop rejections

by the packer or processor.

Andy Moore picked up some

practical tips from a potato

harvester workshop run by

the British Potato Council

POTATO crop losses through incorrectly set or badly maintained harvesting machinery costs the industry £2.4m/year, according to a survey funded by the British Potato Council (BPC).

The survey also reveals that UK growers are losing £13.2m/year through damaged tubers – with an estimated 8% of crops either downgraded or rejected due to bruising caused by badly set-up machinery.

In an attempt to make growers more aware of such losses, the BPC has been conducting a series of potato harvester workshops, with help from the Scottish Agricultural College (SAC) and machinery manufacturers.

"Potato growers need to be better educated on how to set-up and maintain harvesters to achieve maximum crop quality and a premium price from packers and processors," says Fraser Milne of SAC. "Although potato variety, harvesting date and soil conditions will affect crop quality, correct machine set-up is vital to ensure maximum returns."

So where is the best place to start when setting up the harvester?

Russell Lister of Grimme says: "Always start with the basics. The harvester should be hitched to the tractor so that its chassis is level with the ground, and drawbar adjusted long enough to allow an adequate turning circle."

After the harvester has been hitched correctly, Mr Lister suggests inspecting the front end, paying particular attention to the diabolo rollers. The diabolo rollers, he says, should be correctly aligned with their rims following each side of the ridge. Incorrect roller alignment will cause one of the rims to ride on top of the ridge.

"Diabolo depth and pressure should be set to the minimum amount required to turn the rollers," says Mr Lister. "Too much pressure will damage tubers close to the surface, while too little pressure will cause the roller to slide over the surface. Pressure can be altered on most old machines by adjusting a crank handle, while modern harvesters will usually provide in-cab control."


After the diabolo rollers, Mr Lister believes inspecting the discs for sharpness and ensuring there is a 10mm to 15mm gap from the shares to give a clean slice in the soil. Too wide a gap will lead to excessive amounts of soil and stones being admitted into the machine, he says.

Correct angle of the shares, claims Mr Lister, will drastically reduce the risk of damage to both the tuber and harvester.

"The shares should be set flush or 10mm lower than the web to ensure a smooth transfer of crop," he says. "Set too deep and tubers will be damaged by hitting the front of the web, too shallow and potatoes will be left in the ground."

For the next port of call, Mr Lister suggests inspecting and setting up the primary web which, along with the secondary web, is claimed to be responsible for up to 30% of damage to tubers if incorrectly set-up.

Web angle, he says, should be set to ensure there is little roll back of tubers, while guide rollers need to be kept as tight as possible to prevent the web moving from side to side.

"After the primary web, the next components worthy of attention are the haulm rollers which cause the most amount of damage to tubers if set up wrongly," claims Mr Lister. "The further forward and lower the rollers, the less haulm removal and tuber damage. While the further in and higher the rollers, the more likely tubers will be caught and damaged."

Mr Lister advises that 70% to 80% of haulm should be removed at the haulm rollers. If all haulm is removed at this point, he believes there is more risk of damage to the tubers.

Next stop second web.

In addition to performing the same checks on the primary web, Mr Lister says the second web should be kept straight rather than concave to prevent potatoes rolling back. Speed, he says, is also important.

"Running the second web too slow will cause the tubers to accumulate and be caught against the haulm rollers," he warns. "Too fast and tubers will have too much room to move and increase speed before hitting something hard."

Other components to check on the second and primary web are damaged rods, worn joining links and web attachment plates. As a final tip, Mr Lister recommends checking the cleaning units at the rear of the harvester.

Spool or spiral rollers, he says, should be inspected for wear and lodged stones, and also run at the correct speed to ensure tubers bubble rather than bounce during transfer. &#42

Above: Start with the basics… The drawbar on the potato harvester should be adjusted so its chassis runs parallel with the ground to ensure level lifting of tubers.

Left: Achieving the correct diabolo pressure is important to maximise harvesting efficiency in wet conditions; this can be set by crank handles (older machines) or by in-cab control box (newer harvesters).

Above: A 3mm gap between the web and haulm rollers should be maintained to minimise the risk of bruising to tubers.

Right: Rear cleaning units, such as spiral cleaning rollers, should be checked for wear and damage and run at the correct speed to ensure tubers "bubble" rather than "bounce" during transfer.