23 August 2002

Simple steps can help protect potato quality

Potato damage at harvest can seem a low priority in

the rush to get crops lifted. But a few simple steps could

slash losses and boost profits. Louise Impey reports

EACH year 8% of potato crops are downgraded or rejected because of mechanical damage and bruising at harvest, costing growers £13.2m in lost premiums, while harvester losses represent a further £2.4m.

Avoiding such losses is straightforward, but there are no shortcuts, says the British Potato Councils Rob Clayton.

"The only option is to prepare the harvester to match the task in hand and then remain vigilant.

"The harvesters web is the major damage area and incorrect settings are believed to be responsible for as much as 30% of the severe damage caused," says Dr Clayton, who suggests a priority list of 10 key issues to consider this harvest.

Harvester condtion and set up

"Check the manufacturers handbook for recommended settings, as wrongly set up machines can cause problems," says Dr Clayton. "The same applies to worn parts.

"The machine must be hitched correctly. The height of the drawbar has to be right and the extension length should allow turning. The harvester should sit level and the wheels, especially the left side, must be aligned correctly."

Loss of tubers from various parts of the harvester also needs investigating. Some tubers can get half out and be forced back, inc-reasing damage scores in a sample.

Trailer or box transfers

"Low levels of damage here are very dependent on operator skill and good team work with the trailer driver.

"Typical drop heights are 1-2m on to hard surfaces, such as trailer or box floors, so the aim is to try to maintain a low drop height on to a soft surface."

Haulm removers/guide fingers

Settings are crucial and will depend on crop condition, advises Dr Clayton.

"Haulm rollers are a site of major tuber damage. Bearing this in mind, aim to remove 70-80% of the haulm at this point. Any more and you will be doing damage."

Guide fingers should be well lined with rubber and web clearance needs to be increased when excessive haulm is present.

Cleaning units

Cleaning units are there to get rid of clods, stones, bits of weed and haulm, so their setting is always a compromise with the crop and conditions.

"There are a number of types and styles, but whichever type you have, correct presentaion of the crop is essential. Avoid large vertical drops and tubers moving fast; crop on-flow and off-flow must be smooth to minimise damage."

Wear and stuck stones are a potential problem with spools, while spirals can suffer from distorted edge gaps and damaged curtains.

Clod breakers and haulm rakes

Clod breakers can do serious damage. "Use only in extreme conditions. If they break clods, they will certainly damage tubers."

Haulm rakes positioned too far down will also damage tubers. "Once again, avoid them where you can."

Web speeds and agitation

"Web speed depends on soil type. On wet, sticky soils a typical web speed to forward speed ratio is 1.1:1, but 0.7:1 on lighter soils."

Dr Clayton advises keeping agitation off wherever possible. "Only bring it in when increased soil separation is needed. Also keep soil on the primary web and have around 85% fill of the secondary web."

Shares/diabolo rollers

Shares should be angled to present tubers tangential to the top side of the web at the nose cone rollers. "Watch out for small gaps around share to web transfer, because that is where tubers can be lost."

The main function of the rollers is to hold the ridge or bed together as the share enters the ground and to regulate depth.

"So ensure correct alignment," says Dr Clayton. "High downward pressure damages tubers close to the surface and may cause tubers to spill out of the side and be sliced."

Web and elevator side gaps

Excessive side gaps on elevators can give rise to tuber skinning and gouging. "Make sure guide rollers are holding the web tight and not allowing it to meander from side to side."

Web gaps also cause tuber damage. "Check covers for wear – they do not last long. Also, watch out for damaged rods, bad joining links and web attachment plates."

Crop susceptibility

Varietal differences can be large, so check when changing crops.

"Susceptibility depends on a number of factors – variety, dry matter content, agronomy, weather and haulm destruction method.

"Some of these are under investigation in BPC research projects. Identification of crops at particular risk is the aim, so that later season management or harvesting technique can be modified."

Operator

Long working hours common at harvest will affect operator concentration. "There can be issues with operators looking for but not seeing damage, or not being prepared to waste time adjusting the machine.

"Skill and teamwork are important, as is training and good maintenance. Give operators all the help they need," Dr Clayton concludes. &#42

After investing so much in growing a quality spud crop, dont let simple lifting and handling slips jeopardise quality at harvest, says the BPCs Rob Clayton.

1 Harvester condition/set up Check at outset.

2 Trailer/box transfers Teamwork to minimise drops and cushion for soft landings.

3 Haulm removers/guide fingers Aim to remove 70-80% of haulm here, any more risks damage.

4 Cleaning units Match settings to crop & conditions. Beware stuck stones.

5 Clod breakers and haulm rakes Reserve for extreme conditions.

6 Web speeds and agitation Keep agitation off wherever possible, match ratios to conditions.

7 Shares/diabolo rollers Angle correctly and avoid gaps.

8 Web and elevator side gaps Minimise gaps to reduce tuber skinning and gouging.

9 Crop susceptibility Match settings to variety and crop characters.

10 Operator Long working hours affect concentration.