using a rod-digger to dig onion bulbs in dense planting

in iran, onion plants are currently broadcast over the majority of onion fields and weeding and harvesting are done manually by seasonal workers. at harvest time, 40 worker-days are required to onion dig just one hectare. this cost could be saved if the operation could be carried out by machine. rear-mounted diggers can only be implemented if 40 cm spacing between rows is allowed for each tractor wheel, which results in a 20% decrease in yield. this research evaluated the feasibility of using front-mounted implements to dig rows of crop bulbs of the same width as the tractor and to dig only two narrow bands in front of the tractor wheels. treatments included installing a rod weeder (rod digger) with attached wind rowers in front of the tractor and a rod-digger at the rear of the tractor. furrowers were attached in front to dig bulbs located in front of the tractor wheels. the feasibility of the treatment applications was evaluated in preliminary field tests where machine performance indices were measured. the effect of machinery treatments and leaf topping before digging on loss and mechanical damage were tested in a typical onion farm in isfahan province. the results showed that the working depth of the rod digger installed in front of the tractor without a draft control system was not consistent and damaged 8% of bulbs mechanically. moreover, insufficient maneuverability of the tractor and a percentage of slippage of the drive wheels were other restrictions to application of the front-mounted rod digger. connecting the rod digger to the rear linkage of the tractor and using two furrowers in front of the tractor wheels was the only configuration for use of such implements in densely planted onions. in this configuration, using foreword tines like moldboard furrowers in front of the tractor was not easy without the use of a draft control system because of the non-uniformity of the working depth. disk plows worked at a relatively uniform depth without the need for a draft controller; slippage and maneuverability of the tractor were also satisfactory. a comparison of the two furrowers in front of the tractor showed that the disk-type furrower caused less loss to the outer layer of the onion bulbs. the drawback to this type was a 4% loss from cut bulbs that emerged in front of the vertical cutting edge of the disk. if just a 20 cm space is provided on the either side of the planted band, a disk furrower attached in front and a rod digger in the rear of a tractor is the recommendable configuration for onion digging under the tested conditions.