Government of New Brunswick

It is very important that mechanical potato harvesters be serviced and prepared well in advance of the harvest season. Trial runs should be made with the harvester to see that it is "ready to go" and to ensure that operator and crew are familiar with the operation. A complete review of safety procedures and practices including mounting and dismounting the harvester, protective clothing and equipment will prevent unnecessary accidents.

Harvester and bruise reduction

Potato harvesting in the region has changed dramatically in recent years. Nearly all growers have changed to harvesters and use windrowers. Machines are now being converted to belted chain instead of hook chain.

A careful selection of pitches, link pattern (ie a combination of links positioned up, straight or down), and link coating thickness (ie effective separating area between the links) should be considered when changing from hook chain to belted chain. The main reason for this is to maintain soil separation characteristics changed by the gentle action of belted chain compared to hook chain.

Bruise reduction information has indicated that considerable financial savings can be realized by using some relatively simple adjustments or modifications to the harvesting machinery. This reduction depends on a number of factors such as the variety, presence of rocks and clods, temperature, soil type, equipment condition and operating practices. One of the most important things to remember is that when potatoes flow smoothly on belts or chains that are full, the damage levels will be the lowest. Run the machine at or as close to capacity as possible.

Bruise reduction can start at the nose of the digger bed. Where conditions permit, a shear that delivers the potatoes at a tangent to the bed will prevent pressure bruising or splitting where the digger rods can contact the potatoes. In operations that windrow, a full width digger bed on the harvester will prevent the crop from flowing over the centre divider, which can cause high levels of damage. Agitation should be done as low as possible on the primary bed so that the soil cushion is greatest. The addition of a self cleaning material to the sides of all beds will largely prevent the buildup of soil which can induce rollback. Carry soil just onto the secondary bed, allowing it to cushion the crop to that point. Conversions and modifications such as an "S" drive will allow the drops to be kept as small as possible and no greater than 15 cm.

The grower should frequently examine the flow of potatoes through the entire harvester, and examine all transfer points between delivering and receiving chains. This will help identify possible locations where padding and deflectors are required to eliminate the loss of potatoes and reduce tuber damage. Particular attention is required with soil separation devices which agitate the crop as well as soil, rocks and clods. Use these devices only when absolutely necessary and operate at minimum speeds.

The wider (92 cm) booms on newer harvesters can create a situation in which one side can have a very low drop and the other, a very high drop. To counteract this, some operators now build their loads from the right side of the truck to the left. The accepted method of loading the bulk body is a continuous front to back to front step piling, in which the depth of the piling is no greater than 45 cm. This reduces the potential of tuber bruising by limiting the drop and rolling action. Lined boxes also reduce damage levels by "cushioning" the first potatoes into the box. Bulk boxes with full width tailgates, that dump into a receiving hopper have also been shown to reduce damage levels.

Chains should be kept full by balancing their speed (capacity) with the volume of crop being handled. Bed speeds and ratios that have been developed and validated in Prince Edward Island are presented. Notice that the speeds of the primary and secondary beds depend on the conditions being encountered. The speeds of the remaining beds depend on the volume of crop being handled. The bed speeds expressed as a percent of forward speed are on the right side of the table. An operator can change the separation of the harvester using the transmission to change ground speed. The capacity of the conveying section of the harvester can be changed by the throttle setting. Thus, once the harvester has been "timed" to speeds within the ranges in the table, a wide range in soil or crop conditions can be accommodated by slight changes in either engine or ground speed. Many farmers report an increase in the overall capacity of their machines, as well as a dramatic decrease in the damage levels.

Bed speed ratios developed in New Brunswick differ from those used in Prince Edward Island due to a dissimilarity in field and climatic conditions. Due to the topography of the New Brunswick Potato Belt, it is recommended that secondary bed speeds never be operated below 1.6 km/hr to prevent backfeeding at the interface with the rear cross. Average ground speeds range between 1.6 and 2.5 km/hr for New Brunswick conditions. Bed speed ratios should be within a 10% range of those illustrated in the table. Note that the Table is set up at a constant tractor rpm. Varying tractor rpm and gear selection will allow the operator to change the ratio of bed speed/forward speed when harvest conditions are very damp or dry.

It is recognized that conditions in the region are very different and that the exact numbers in the table will not necessarily work in all areas. The fundamentals are valid, however, and the speeds and ratios for any specific area can be developed. Contact the engineering group in your area for specifics.

Airheads are another area of concern. Inside the unit, the bottom of the sorting table should be covered with a self cleaning material to prevent dirt build-up. The dividing edge between the airhead and table beds should be cushioned with rubber so that bolt heads do not protrude. The inside hook chain bed should be removed and a pan or series of padded rods installed. Efficiency can be increased an average of 7 to 10% by proper sealing of the unit. Another advantage of sealing airhead leaks is even separation resulting in even loading and reduced bruise damage. Operating the hump in the lowest possible position will allow large rocks to exit with minimum damage to tubers and maximize separation area.

P.E.I. Conditions

% OF F.S.*
a) Primary
b) Secondary
dry wet
0.67 1.1
0.52 0.69
dry wet
75 130
55 80
a) Rear Cross
light heavy
0.56 0.79
light heavy
80 100
a) Side Elevator
b) Star Table
c) Boom
light heavy
0.50 0.61
80 rpm 90 rpm
0.41 0.46
light heavy
60 80
50 65

* F.S. = Forward Speed (Range 2.4-3.5 km/h)


Harvester bed speeds in KM/H *
(Constant Tractor RPM)

  Four row harvesting (two rows windrowed)
for 914 mm beds
Four row harvesting (two rows windrowed)
for 737 mm beds

% Ground
% Ground
Beds km/h km/h km/h   km/h km/h km/h  
Primary 1.6 1.9 2.4 100 1.6 1.9 2.4 100
Secondary 1.6 1.9 2.4 100 1.6 1.9 2.4 100
Diviner 1.6 1.9 2.4 100 1.6 1.9 2.4 100
Rear Cross 1.29 1.6 2.06 85 1.6 1.9 2.4 100
Side Elevator 1.29 1.53 1.93 80 1.53 1.87 2.25 85
Air Head 1.29 1.53 1.93 80 1.53 1.87 2.25 85
Boom 1.29 1.29 1.29 55-80 1.21 1.21 2.21 50-75

* Conversion 1 km/h = 0.28 m/s = 0.62 mph


The use of windrowers is a common practice. It is effective for opening fields, reducing harvester travel, and proper loading of harvester beds to capacity. Windrowers can cause as much bruising of potatoes as the harvester, but are often overlooked. Places where the tuber damage can occur are very similar to corresponding beds of a harvester. The speed of the rear cross should be sufficient to carefully place tubers on the ground without causing back feeding at the secondary and rear cross interface.

Excessive speeds on the rear cross can increase tuber damage. If the soil surface is rocky or packed, then slight tillage between the rows can be accomplished using a secondary tillage tool (ie S tyne, spring tooth).

Tuber condition

The skin of the tuber must be hardened or suberized. Do not harvest earlier than 10 days after the vines are dead. Hydrated potatoes are more resistant to blackspot and more susceptible to shatter bruise than dry potatoes.

Bruising and soil temperature

Soil temperature at the time of lifting the tubers from the row is the most important factor that affects the ease with which potato tubers bruise.

As potato tubers are cooled, less force is required to rupture the skin and cause bruises. Since the temperature of the tuber is almost the same as the soil temperature, potatoes should not be harvested when the temperature is less than 4oC. Use extreme care when harvesting at soil temperatures less than 9oC.

Many potato growers work in the field from 6 a.m. to 6 p.m. during the growing season. At harvest time, and particularly in the latter part of the season, change your hours of work (for example, form 10 a.m. to 10 p.m.). By doing this you avoid the cool morning temperatures and take advantage of a warmer soil later in the day.

Use a bruise detection kit and check frequently for bruising at various points on harvesting and storage equipment.

A Catechol solution is used to detect shatter bruising where skin surface is broken. Blackspot cannot normally be detected using this method. A rapid test for this has been used (tetrazolium test) involving the chemical 2,3,5 triphenyltetrazolium chloride diluted in water. This test still requires between 45 minutes to one hour and even up to 2 hours when the temperature is between 4oC and 8oC.

Catechol treated tubers are poisonous and should be disposed of according to provincial recommendations.


Some points to consider in the use of a bin loader --

  1. Keep drops less than 15 cm.
  2. Pad hard surfaces on hopper and conveyor sides.
  3. Use padded baffle boards or straw-filled bags to help reduce tumbling and rolling in the bin.
  4. Use a boom long enough for the height you want to pile. Some bin piler boom lengths for various maximum pile heights:
    pile 2.4 m boom 4.2 m
    3.6 m 6.4 m
    5.5 m 9.7 m
    6.0 m 0.6 m
  5. Avoid leaving the boom in the same place for too long in order to prevent the build-up of a cone of soil which could cause ventilation problems.


Blackspot and shatter bruises result when bruising forces are applied to the tubers. Blackspot does not usually penetrate or rupture the potato skin. Shatter bruises usually break the skin and may penetrate deeper. Bruise susceptibility is influenced by tuber condition, temperature, soil condition and harvester operation.