Mechanical Harvesting of Pecans

Mechanical Harvesting of Pecans

Pecan Research

WILLIAM H. ALDRED and TOM E. DENMAN*


PECAN GROWERS for the first time have a choice of methods for harvesting their crop. They can use the familiar hand harvesting method of the past with all of its problems of ever increasing cost, unavailability of workers and in-efficiency; or, they may choose mechanical harvesting. This should be good news to pecan growers who have waged a consistent but losing battle against harvesting costs.

The development of machines capable of harvesting native pecans has been hampered by the extreme variability of the many orchards scattered over a wide area. Although the native pecan timber is concentrated in creek and river bottoms, the topography of the land through which the streams flow is so variable that each orchard has its own distinct problems. Groves located among major rivers frequently have a silt-type soil which cracks readily on drying and forms small clods which are the same size and shape as the pecans. Orchards located along the smaller streams are subject to sudden swift overflows which remove soil and deposits coarse sand leaving a rough terrain. The accumulation of trash and the growth of vegetation during the summer increase the difficulties of mechanical harvesting.

Types of Machines

Pecans can be retrieved by several different methods, but most machines on the market today utilize the sweeping principles. Ramps are used to assist in transporting the nuts, leaves and trash into the machine, figure 1.Various flexible materials, such as strips of rubber or nylon bristles, are attached to the lower edge of the ramp to insure its following the contour of the ground and aid in deflecting the pecans and trash up the ramp.

Steel bristle brushes were used in earlier harvesters. This type of brush retrieved a high percentage of the nuts under ideal conditions, such as level soil with a good turf cut to the correct height. Difficulties were experienced in retrieving pecans from uneven ground and the brushes were damaged by repeated passes over ridges.

Rubber fingers or strips of flexible rubber are employed by most manufacturers for sweeping the nuts into the machine. The harvesting efficiency of the various machines which uses rubber fingers apparently is not affected by the size, shape or length of the fingers if the brush is properly constructed and adjusted. The longer rubber fingers would seem to insure continuous contact with the ground in rough areas. The life expectancy of the many types of fingers available has not been fully evaluated, but they have been known to operate through one season with little sign of wear. The rubber fingers can be replaced as needed with little effort and cost.

After the nuts, leaves and trash have been elevated from the ground into the machine by rotating brush, blowers of various types are employed for removing leaves and lighter trash while all the material is airborne. Several machines use an axial flow blower for removing the lighter foreign materials while the nuts, heavy trash and sticks drop onto a cross conveyor located in front of the brush, figure 1. The larger sticks ride the conveyor out and drop to the ground while pecans fall through slotted openings in the conveyor onto an elevator. Some machines elevate the pecans and trash 2 feet off the ground by sweeping them up a 180-degree curved ramp onto a conveyor. The conveyor carries the nuts through an air stream to remove the light-weight foreign materials.

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*Assistant professor-farm machinery, Department of Agricultural Engineering, Texas A&M University, and associate horticulturist, West Cross Timbers Experiment Station, Stephenville.


pecan harvester pre savage

 

Fig. I. Rubber finger sweeper drum, ramp and conveyor.

pecan cleaner pre savage

Fig. 2. Rotating drum cleaner for removing dirt, clods, small trash, leaves, hulls and large sticks.

Most machines incorporate a second cleaning device, such as air, vibrating screens, and augers with slotted bottom or sloping belts, into the elevator or auger which transports the nuts to a bulk container or bags. All of these cleaning devices can remove a large percentage of the dirt clods and other foreign materials when properly adjusted and operated at the correct speed. Some difficulties were experienced in maintaining a constant angle on the sloping belts when the machine was on unlevel ground.


Harvesters are available as self-propelled or tractor-powered models. Self-propelled types are either a small 2 feet wide unit with little or no cleaning

pecan stick remover cleaner

Fig.3 Incline double belt cleaner for removing sticks.

equipment or large units which will harvest an area 6 to 7 feet wide. Harvesters which use tractors as power units are usually offset pull type or internal mounted on the front of the tractor. They receive their power from the tractor PTO or are hydraulically driven.

Cultural Practices

Most native pecan groves require some land preparation for successful mechanical harvesting. Land preparation such as sloping the bank of dry streams and gullies, filling small holes, smoothing ridges, depressions and sand dunes should be carried out in winter during the dormant season. This reduces the possibility of damage to the trees, and enables grass to cover the bare ground before harvest. Smoothing the soil will increase the efficiency of the harvester and reduce considerably the hazard of damaging the machine and possible injury to the operator.

The importance of controlling the growth of vegetation during the summer and fall cannot be overstressed. Grass and weeds should be mowed close, 2 to3 inches, several times during the summer for vegetation to decay before harvest time. If growers do not control vegetation during the summer and early fall but wait until the shucks split to shreds, they will produce a mat of weeds and grass which will clog the pick-up units of the harvester.

Harvesting Tests

An experimental pecan harvester was built and field tested in 1966 for evaluating basic principles. Machine evaluation consisted of harvesting test areas in a native orchard where a mechanical shaker was used. The number of pecans in each plot was counted before and after the harvester had made one pass. The harvesting efficiency after one pass of the machine ranged from 80 to 92 percent, Table 1. When the harvester was run over the plots a second time immediately after the first harvest, the combined harvesting efficiency increased to from 96 to 99 percent.

pecan inspection table conveyor

Fig.4 Chain belt for transporting pecans from stick remover to pop remover and bagging attachment.

Cleaning Equipment

Field tests indicate that mechanically harvested pecans may contain 35 to 55 percent trash; therefore, additional cleaning will be required before they are sold. Preliminary tests indicate that a stationary final cleaner can perform this task at a lower unit cost than building the cleaning equipment in with the harvester.

Table 1.Effect of pre harvest treatment on harvesting efficiency

Pre harvest treatment¹ Percent nuts Percent nuts

retrieved retrieved

first harvest² second harvest³

Dump rake 87.85 96.37

Dump rake and steel

brush sweeper 84.02 97.10

Steel brush sweeper 89.57 97.94

Rubber finger brush sweeper 86.36 96.52

Side delivery rubber

brush sweeper 92.63 99.17

Check 80.87 97.40


An experimental cleaner was built and evaluated in 1966.The cleaner contained a rotating rod drum with 3/8-inch spacing between rods for removing dirt, clods, small sticks, leaves, husk and small stones. A second section of the rotating drum has adjustable spaces between the rings to facilitate changing the

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¹Preharvest treatment removed trash from area under trees after the pecans reached maturity and prior to the shuck, splitting.

²Tests with ouly one passes of pecan harvester over area. 

³Tests with two passes of pecan harvester over area. Results are total harvest efficiency for both passes opening for the different variety of pecans, figure 2. The nuts fall through the opening into a conveyor hopper while the large sticks, which cannot pass through the opening, are carried out the end of the drum. The nuts are elevated to a sloping double belt stick remover where the difference in the coefficient of friction between the moving belt, nuts and sticks is used for separation, figure 3. The sticks, which have more friction than the pecan, will move up the incline with the belt in feet per cinute, angle of the inclined belt and the difference in the nuts fall from the stick remove onto a chain belt where a. "pop" remover will suck out the pops and additional trash, figure 4. Any remaining foreign material can be removed by hand from the chain belt as the nuts pass on to the bagging attachment. The percentage of foreign materials removed by drum and belt cleaner operating in series is shown in Table 2.


Separation of the sticks from the pecans depends upon the surface speed of the belt in feet per minute, angle of the inclined belt and the difference in the coefficient of friction. Therefore, it is desirable for a stack remover which utilizes this principle to have a means for easily adjusting belt speed, belt angle and feed rate.


Table 2.Foreign material removed by drum and belt cleaning

equipment operating in series

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Drum Belt Remaining

Test of total Pounds  Percent       Percent

Number Pounds Percent of total pounds        of total

A 18.1 72.4 6.5 26.0 0.4 1.6

B 16.9 67.6 7.5 30.0 0.6 2.4

C 18.7 74.8 5.4 21.6 0.9 3.6

D 20.7 82.8 3.8 15.2 0.5 2.0

E 22.4 89.6 2.4 9.6 0.2 0.8

F 14.5 58.0 9.3 37.2 1.1 4.4

G 9.0 36.0 15.2 60.8 1.1 4.4

H 13.0 52.0 10.3 41.2 1.7 6.8

Average 66.0 31.0 3.0

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