Yield and fruit quality of 'Van' sweet cherry in four high density production systems over seven years

An intensive orchard of 'Van' sweet cherry trees (Prunus avium L.) all grafted on the semidwarf rootstock Damil was established in 1991 at Ullensvang Research Centre, western Norway at 60 degrees North. The objectives were to evaluate four different single row planting systems (vertical axis, free spindle, vase-shaped and Y-trellis) and three planting densities (1.5, 2.0 and 3.0 x 4 m and 0.5, 1.0, 1.5 x 4 m for the Y-trellis trees) in a northern climate. These planting distances gave a range of tree density of 1670 - 5000 trees per ha. The experiment was located on a loamy sand high in organic matter and trickle irrigation was provided. Soil management was grass in the alleyways with a vegetation-free strip along the tree rows. Annual data of yield, fruit size and internal quality were recorded. The experiment was rapidly established and gave already a small yield the year after planting on the vertical axis trees. During the first years the yields per ha were positively correlated with tree density. Cumulative yield per hectare was highest on the Y-trellis trees with the highest density (5000 trees per ha). Already in the third leaf, this system gave 14.5 tons per hectare. The yields the following years have slightly declined. Vertical axis trees have increased the yields for all the planting densities every year. In the 6th leaf this canopy system spaced 2x4 m produced 16 tons per hectare. The same trees had the highest yield efficiency. All canopy systems had a low yield in the 7th leaf due to unfavourably pollination conditions. 'Van' fruit weights averaged 8.6 g and no differences between either canopies nor densities were found. The fruit content of soluble solids was high for all combinations (17.6 % on average), but increased with decreasing planting densities. A tendency of reduced concentration of fruit soluble solids of the Y-trellis trees was registered.