Abstract
Plum trees of ‘Elena’, designed for mechanical harvesting with a straddle self-propelled harvester, were planted in 2008 in the experimental orchard at Dąbrowice at a distance of 4 × 1.5 and 2.0 m. The trees were trained to a central leader to a height of 2.7 m and 1.5 or 2.0 m spread. Plum trees designed for mechanical harvesting with a small tractor-driven harvester were spaced at 4 × 1.0 or 1.5 m and were trellised horizontally on wires stretched along rows 0.8 m above the ground. Fruits were harvested in 2012–2015. The cumulative yield from the trellised trees was only half of that from the trees trained to a central leader, whereas the fruit load index (weight of fruits per m3 canopy) was the highest at 4 × 1.0 m). To explain this phenomenon, studies were conducted in 2015 on light relations in the two training systems. The studies revealed that light transmission has different patterns in the two training systems, but the level of light interception was nearly similar. Light distribution was more beneficial for photosynthesis in the central leader trees. The trees trained to a horizontal canopy had poor illumination at the canopy base. The main reason of low productivity of the horizontal canopy was low canopy volume.