The relation of hand-harvesting cost in plum and prune production to the total costs amounts to 25-40%. Mechanical harvesting makes it possible to cut drastically both the harvesting and total costs. To test the suitability of plum and prune species to be mechanically harvested, an experimental grove (area 0.8 ha) was established in 2008. Three plum cultivars and one prune cultivar grafted on semi-dwarf and vigorous rootstocks were planted at high density (1250; 1666; 2500 trees·ha−1). During the span of full yielding (2012-2014), fruits were harvested mechanically with a canopy contact, straddle harvester in continuous motion, designed at the Institute of Horticulture in Skierniewice, to harvest tart cherry, and later adapted to harvesting plums and prunes. Trees grafted on semi-dwarf rootstock (‘Wangenheim Prune’) appeared to be more suitable for mechanical harvesting than strong-growing trees grafted onPrunus cerasiferaclone ‘Myrobalan’. Cumulative yield per ha (years 2012-2014) was the highest at the highest planting density. Trees grafted on the semi-dwarf rootstock had a higher productivity index than trees grafted on the vigorous rootstock. There was no significant difference in fruit quality related to planting distance. Mechanical harvesting was nearly 40 times more efficient than hand picking. The efficiency of mechanical harvest was from 85% to 90%. Over 5% of fruits were lost on the ground and from 1 to 5% of fruits were left on the tree. Up to 18% of the plums and no more than 10% of the prunes harvested mechanically showed some damage. They can be fully acceptable for processing, for up to 10 days, providing the potential deterioration processes are inhibited by cold storage. The large-fruited cultivars seem to be more susceptible to bruising than the small-fruited ones. For the latter, the share of marketable quality fruits within the mechanically harvested crop amounted to about 80%, which could be a good prognostic justifying further trials on the prune harvester.

Plums, sweet cherry, and sour cherry trees were spaced 4.5 m × 1.5 m to be trained to "Y" and "V"-trellising systems for mechanical harvesting, with a canopy contact harvester, attending to obtain fruits meeting the requirements of the fresh fruit market. The applied trellising systems were compared with the standard central leader system at the same spacing. The most of trellised trees grew less vigorously than the standard trees, and after 3 years of training, the trees were suitable for mechanical harvesting with the harvester designed at the Research Institute of Horticulture in Skierniewice. The trellised trees were able to set as many fruitlets as those grown in the form of central leader and gave a comparable yield, but differences between cultivars were significant. Light interception in the third year after planting was lower for trees of sour cherry and plum growing in the "Y"-20° and "V" in comparison to the trees with central leader. Illumination of trellised canopies at the level of 0.7 and 1.5 m was the most favorable in "V" system when compared to control and "Y" training systems. Cost of construction for the trellising systems of stone fruits calculated per 1 ha was two times higher when compared with the standard system.

Two plum cultivars ‘Record’ and ‘Empress’ and one prune cultivar ‘Common Prune’ were planted in spring 2014, spaced at 4.5 × 1.5 × 2.0 m, to be trained to the “Y”- and “V”-trellising systems for mechanical harvesting of dessert fruits with a canopy-contact harvester. The applied trellising systems were compared with the standard central leader system at the same spacing. Trellised trees showed a tendency to grow less well than leader-trained trees, but during the four years of training, they created a higher canopy volume than the control trees because of their spreading form. Trellised trees were able to give yields comparable to those of standard trees. Light distribution within the tree canopy was acceptable in all the training systems. After 4 years of training, the trees were suitable for mechanical harvesting. The effectiveness of mechanical harvesting varied from 85% to 90%. The quality of the fruits harvested with a canopy-contact harvester was comparable to that of manually picked fruits. The consumption of quality of fruits after mechanical harvesting rated on a 5-grade scale was 0.5 grade lower than that of manually harvested fruits. These fruits were acceptable in the local fruit market. Mechanical harvesting was 10–30 times faster compared to manual picking. The cost of the trellising system calculated per 1 ha was 2.0 times higher than that of the standard system.

No abstract

The aim of the study was to determine the possibility of harvesting raspberries with a pulsating air stream that causes the shoots of plants to vibrate. Two tractor-driven test devices were developed under this specific objective. The first one was a high capacity compressor, and the stream of air produced by it was directed onto one side of a row of plants. The second one was a device producing two counter-flowing air streams colliding in the middle of a row of plants. The frequency of the air pulses was adjusted steplessly by varying the rotational velocity of the shutters closing and opening the outlets of the fans. In the field trials with the device based on a compressor-generated air stream, two air pulse frequencies were used: 500 and 540 pulses per minute (8.3 and 9 Hz). The mean detachment force was 0.727 N. About 50% of ripe raspberries were removed from the bushes. The results achieved during harvesting with the device operating on the principle of colliding two pulsating air streams were markedly better and put the harvesting effectiveness within the range achieved in the trials with combine harvesters with mechanical finger shakers conducted by other researchers. For two pulse frequencies (8 and 9 Hz), almost 62% of fruits were harvested. Increasing the pulse frequency of the counter-flowing air streams above 9 Hz did not improve the effectiveness of detaching raspberry fruits from shoots.