Robert G. Holmes,
Department of Food, Agricultural, and Biological Engineering,
Ohio Agricultural Research and Development Center,
The Ohio State University,
Columbus, Ohio.
Don Wuertz,
Agricultural Research Service,
United States Department of Agriculture,
Columbus, Ohio.
Identification of ornamental yews as a potential renewable source of Taxol and related taxanes has led to the need for efficient, effective methods for growing, harvesting, drying, storing, and handling Taxus clippings and needles. Communication with Bristol-Myers Squibb suggested that the demand (during 1993, 1994, 1995) for Taxus biomass would be met with bark from Pacific yew trees that were already under contract to be harvested and from naturally occurring sources in Nepal and India. However, many citizens of the United States and other countries are opposed to the harvest of naturally occurring trees and shrubs because of perceived insults to a stable environment. For example, on average, three to four Pacific yew trees, each 150 to 200 years old, would have to be sacrificed to obtain enough Taxol to treat one ovarian cancer patient.
A sensible alternative would be to harvest clippings from cultivated ornamental yews commonly grown in nurseries. For selected cultivars, clippings could be captured and processed as a by-product of annual pruning activities. Since the entire plant is not sacrificed, the potential for providing a renewable source of Taxus biomass is evident. The nursery grower would be in a position to grow dual purpose plants - clippings for the pharmaceutical marketplace and shrubs for the ornamental marketplace. Clipping is normally done with hand shears or by using a powered hedge trimmer. Both are labor-intensive operations.
The machine shown in Figure 1 was designed to mechanically cut and collect the clippings from the top of upright growing plants such as Taxus x media 'Hicksii.' The machine was powered by a medium-sized tractor (30 to 40 hp) and was constructed by modifying the header from a small grain combine.
The standard cutter bar and guards were replaced by 1-1/2-inch-wide "quick cut" knives and guards. In addition, the conventional knife hold-down plates were replaced by special 1/4-inch-thick hold-down plates on top of each guard to give a cleaner cut and prevent the small clippings from falling through the knife and being recut and lost on the ground (see Figure 2).
The standard reel was modified by reducing its diameter to 38 inches, by installing 12 batts in place of the normal six and by fastening 1/8-inch thick flexible rubber belting along the edge of each reel batt to "sweep" the cuttings off the cutter bar and back onto the canvas conveyor. With this system, a clean cut was achieved, and almost no cuttings were lost on the ground.
After being cut, the clippings were conveyed up the canvas conveyor and deposited into a 60-inch x 30-inch x 18-inch plywood collector box shown at the rear of the harvester (Figure 3). The collector box was constructed with a wire-mesh bottom to retain the clippings and needles but allow free airflow up through the plant material for drying.
The cutter bar, reel, and conveyor were all driven by hydraulic motors powered from the tractor hydraulic system. In addition, the entire machine and the header can be hydraulically positioned (independently) to allow trimming of plants from four inches to 30 inches in height (Short et al., 1999).
When full, the front pallet box was slid to the rear, and the empty box was moved to the front (see Figure 4). A full box containing approximately 225 lbs. of clippings was off-loaded from the harvester to a truck or trailer and hauled to a dryer.
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| Figure 1. View of Taxus clipping harvester during field operation. | Figure 2. Close-up view of "quick cut" knives and guards. |
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| Figure 3. Plywood collector box showing wire-mesh bottom. | Figure 4. View of two-pallet collection system. |
During 1992 approximately 1,000 acres of various Taxus cultivars were clipped with this machine. Ground speeds up to 1-1/2 mph were used. The rate of harvest varied considerably, depending on the plant spacing, age, cultivar, and growth conditions. Both five-foot-wide beds and three rows of individual plants were harvested. Maximum harvest rates of 300 lbs./hr. were attained while harvesting Taxus x media 'Hicksii' while rates up to 1,350 lbs./hr. were attained while harvesting Taxus x media 'Densiformis.'
Future plans are to:
Short, T. H., R. E. Young, and R. C. Hansen. 1999. Mechanization of Landscaping and Outdoor Nursery Crop Production: Planting, Harvesting, and Handling. Video, 12 minutes. The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio.