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A SINGLE-HILL POTATO DIGGER G.C. Misener and L.P. McMillan I In the course of its potato breeding program the Fredericton Research Station each year grows about fifty thousand single hill plots o f material in its first field generation. Each of these single hills must be separately harvested as part of the selection process. This operation was normally carried out by a gang of workers digging by hand, followed by a team of selectors. Mechanization of the digging was seen as a necessary corollary to improved labor utilization in the breeding program. Dijkstra (2) describes a machine developed for harvesting potatoes in experimental plots. The potato lifting section which includes the digging share, depth control wheels, rod link elevator, haulm separator and cross conveyor is located at the front of the tractor. The potatoes are conveyed to the separator belt by a side-mounted closed conveyor belt. A detachable bagging device is fitted to the end of the separator belt at the rear of the tractor. Chase et al. (1) describe a self-propelled plot harvester equipped with a sizing table. The objective of the design of the single-hill digger was to develop the capability of digging hills of potatoes spaced at 75 cm and depositing them on the soil with the vines while not mixing tubers f r o m adjacent hills. The design adopted for the digger is shown schematically in Figure 1. The digging elevatoi" bed operates at an angle of 15 ° with respect to the horizontal and is hydraulically powered to permit m a x i m u m flexibility. Depth wheels with haulm cutting colters are located opposite the digging share. The hydraulic drive operates f r o m the tractor's hydraulic supply and requires a fluid flow of up to 36.0 e/min. The entire digger is three point-hitch m o u n t e d allowing quick turn around and ease of transportation. The colters were able to effectively cut the haulms adjacent to the digging share. This action prevented the haulms from dragging along the side o f the digger which would have displaced: the tubers on the chain. Blade length was found to be critical with respect to the flow of material onto the digging bed. A straight blade of width 21.6 cm was found to allow an even flow o f soil under a wide range of soil moisture content. The distance between the blade and digging chain was made adjustable to accommodate varying soil conditions. Thirty lots of four cultivars of potatoes were alternately planted at 75 cm spacing. Each cultivar had a different skin color or texture which allowed quick identification of a specific cultivar. With the alternate planting, mix'Research Scientist and Research Technician, Research Station, Agriculture Canada, Fredericton, New Brunswick. E3B 4Z7 Received for publication August 30, 1982.

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SHORT COMMUNICATION

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ing of tubers between hills during harvest could be easily noted. The results from this test indicated that no mixing between adjacent hills o f potatoes was observed. Tests were conducted with a worker walking on each side o f the digger in order to assure that the haulms passed through the machine without catching. By using the digger, the harvesting crew could double their daily output. The digger was also found useful for digging small plots other than the single hills. The use of the digger has improved the effectiveness and efficiency o f the harvest crew. It also presents the potatoes in a uniform and good manner which makes it easier for the selectors to do their job. The digger which is equipped with a hydraulic drive was found to be very flexible and could acc o m m o d a t e variable harvest conditions. Literature Cited

1. Chase, R.W., N.R. Thompson, R.L. Ledebuhr, C.M. Hansen and R.B. Kitchen. 1978. Plot harvester for potatoes. Am Potato J 55:235,237. 2. Dijkstra, J. 1976. Some aspects of experimental field mechanization in the Netherlands. Proceedings of the Fourth International Conference on Mechanization of Field Experiments. 314-320.