ISHS Acta Horticulturae 175: Symposium on Physiology of Productivity of Subtropical and Tropical Tree Fruits
RESEARCH AND PROGRESS IN CULTURAL SYSTEMS AND MANAGEMENT IN TEMPERATE FRUIT ORCHARDS |
| Author: | D.J. Chalmers |
| Abstract:
Early bearing and high yields per ha, have the most effect on protitability of orchards and, consequently, have been the aim of much tree management research. It is now possible to obtain commercial crops as little as 18 months after planting and to have fully developed orchards, capable of maximizing yield, within 3–4 years of planting. The three main research avenues that have led to this situation are tree density, tree size and tree shape. Early commercial bearing is not possible at low tree density. High density planting (HDP), however, may also facilitate efficient light interception and high yields in mature orchards. On the other hand, when trees in HDP have filled their allotted space, management becomes a challenge because most fruit trees are planted at higher densities or allocated less area than the tree normally occupies when fully grown. The resulting overcrowding leads to declining productivity. Research workers have developed a number of methods to control tree size. Most temperate tree species now have dwarfing rootstocks but with the exception of apples and perhaps pears, as many problems have been created by dwarting rootstocks as have been solved. Growth retardants, and lately, especially paclobutrazole (PP333), have been used successfully. Summer pruning can control tree size and if severe enough will limit the tree to any desired size. When very high densities are required (>1500 trees ha-1) summer pruning must be too severe and results in compensatory growth, which suppresses fruit quality and yield. Tree shape has also been used to fit trees into a limited space. Cordon systems such as spindle, axe and Tatura trellis allow trees to grow to their limit within a confined space. Regulated water deficits are proving a very effective means for controlling tree size. The simple view still prevails that yield per ha will be maximized if all the light falling on each ha is intercepted by the foliage canopy. This assumption, however, does not apply for fruit crops. When the canopy closes the light quality deteriorates within the canopy where fruit and developing buds are located. In addition photosynthesis is stimulated in leaves supporting nearby fruit. The most fruitful orchard canopies must therefore transmit sufficient light for fruit bud initiation and fruit set within the canopy as well as allowing leaves near growing fruit to be well illuminated. Although one invariably finds that rate of economic return is better for HDP than conventional systems the establishment cost per ha remains a disincentive for commercial orchardists. Further, for tree crops, the nursery stage adds to the time required to bring a new orchard into production. Consequently systems for rapid or cheap propagation have been extensively studied in recent years. | |
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