HIGH-DENSITY PLANTING: DEVELOPMENT AND CURRENT ACHIEVEMENTS IN THE NETHERLANDS, BELGIUM, AND WEST GERMANY

Developments in orchard types (tree sizes, tree shapes, and planting systems) over the last 80 years are outlined. During this period the orchard with relatively few large trees per ha and grown on seedling rootstock gradually made way - via many intermediate forms - for high-density plantings with many small spindle-type trees per ha on dwarfing rootstocks (mainly M.9 for apple and Quince A or C for pears). The reason for this change was the need to achieve early cropping, regular high yields, and low labour requirements in order to meet the continually increasing costs of production. That this intensification yielded the desired results can be seen from some Dutch figures: in the 1950–1977 period the average yield from an apple orchard increased from 16 to 38 tons per ha, and the man-hours required per ha for cultural practices (excluding picking) decreased from 550 to 175.

Therefore, the question is no longer whether to plant densely, but how densely. Fruit-growers have apparently come to different conclusions on this point, since the number of trees planted per ha ranges from 1 250 to more than 5 000 for apple and from 1 500 to 2 500 for pear. These differences are influenced by the size of the holding and the expected vigour of growth as determined by cultivar and soil quality. As to arrangement, the single row is still the favourite system. Multi-rows (two to six rows wide) are planted on a limited scale, mostly as well-devised three-row beds.

The advantages of the single-row design are obvious: it gives a reasonably light distribution within the canopy (favourable for the average fruit quality) and easy management due to the many alleyways. One drawback of this design is that with very high tree numbers per ha, light interception is far from maximal due to the many alleys and so is the yield capacity of the orchard. Moreover, average fruit size may be reduced when tree distances within the row become small.

With multirow systems, light interception increases and with it the production potential of the orchard. However, light distribution and thus average fruit colour may become less optimal. With very many trees per ha, one of the advantages of the multi-row systems, i.e. ample space per tree resulting from the sacrifice of alleys, is lost and average fruit size and colour may be prejudiced. Additional disadvantages are the poor accessibility of the canopy for management and spray droplets as compared with single rows. The latter problem can lead to higher incidences of pests and diseases in the middle parts of the multi-rows.

Now that the market is making ever-higher demands with respect to fruit size and colour, the planting system and the number of trees per ha must be chosen with care to provide the maximum yield of easily marketable fruits. This requires even more careful planning by the grower of the planting density and arrangement in relation to site and cultivar vigour.