Closer planting of peach trees in Goulburn Valley orchards
Closer planting of peach trees has gained favour in many parts of the world because it contributes to the following aims:
- Early productivity, resulting in an early return on capital invested.
- Lowered cost of production.
- Quicker and easier adjustment to changing economic conditions by promotion of rotation orchards of young trees, or orchard recovery from tree losses caused by wet winters.
Early productivity is very important, particularly for peach trees that have an economic life of 18 years or less. However, even for the simplest form of closer planting, such as doubling the number of trees within the row, it is necessary to have a different tree shape and management technique to ensure that a fruitful canopy is maintained . Results from earlier work at Tatura showed that by planting trees 3.2 m or 4 m apart within the row, yield increased during the first 11 years by 58 or 68 tonnes/ha respectively. This increased the net return by up to 70%. Trees were vase-shaped and it was clear that, in the closer 3.2 m planting in particular, shading already limited productivity.
Competition for light by limbs and nearby trees causes bareness in the shaded parts and forces the cropping zone higher and higher. The more closely vase-shaped trees are planted, and the taller they grow, the greater this problem becomes.
Following that early work, trees were modified to a more upright shape by pulling the limbs in with wire, thus creating gaps in the upper canopy and allowing light to penetrate. Light interception in the lower part of these multiple upright leader trees improved and this rejuvenated shoot growth. As a result, trees continued to produce an extra 4-5 tonnes/ha a year, compared with conventional plantings. Later work confirmed that closer planting of trees in semi-hedgerows with up to 660 trees/ha will recover establishment costs more rapidly than traditional plantings and this advantage is maintained in later years.
Principles of hedgerow plantings
At present, commercial experience in the Goulburn Valley is limited to double plantings within the row, and row spacings ranging from 5 to 6 m. Trees in these plantings still tend to have an individual bearing surface and are therefore not true hedgerows. A hedgerow is the result of natural evolution from closer planting of vase-shaped trees and has a continuous canopy wall along the row. The ultimate cropping potential per unit of land, after trees have filled their allotted space, depends on the total volume of the hedgerow mantle (bearing surface) where fruiting primarily occurs.
The fruit-producing area and depth, or tree mantle, are the result of tree training and depth of penetration of light for cropping. With careful management this level of light penetration is between 0.5 and 1 m. Hedgerows use light most efficiently when they run north-south. They should be broader at the base than at the top. As a general rule the height of the hedgerow should not exceed twice the width of the alleyway needed for tractors and implements. For a row spacing of 5.5 m and an alleyway of 2.2 m we can have a hedgerow that is 3.3 m wide at the base and 4.4 m high. The fruit-bearing volume of such a planting is greater than that for standard vase-shaped trees.
Early productivity is, however, largely a function of tree density. Closely planted trees fill their allotted space earlier and the more intense root competition increases fruitfulness.
If trees are produced at a lower cost from cuttings, higher tree densities within the hedgerow become a more attractive proposition. For instance, at Tatura, a planting of hardwood cuttings at 4 x 1 m (2500 trees/ha) yielded 6.7 and 24.7 tonnes per ha in the second and third growing season respectively. Trees are trained as self-supporting central leaders.
Such a planting repays its capital cost within three years. However, it requires greater management skills to maintain a fruitful canopy.
For semi-intensive plantings (up to 660 trees/ha) both the central and multiple upright leader tree-shapes have been used. Central leader trees are self-supporting and produce a larger proportion of their crop in the lower half of the tree. However, trees become less accessible, unless provision is made for alleyways to reach the centre. For higher tree-densities and row-spacings of 5 m or less, suitable tree-shapes are central leader trees or fan (palmette) shaped trees with three scaffold limbs.
Training and management
When training young trees the aim must be to fill the allotted space as quickly as possible. Summer pruning is essential to achieve this. Initially summer pruning is necessary to maintain apical dominance of the scaffold limbs of the tree-shape selected. Competing, vigorous shoot growth must be suppressed. Periodic attention during the summer months ensures a better tree-shape, that requires less winter pruning. The tree is also bigger. True hedgerows have a continuous bearing surface along the row; it is therefore essential to completely fill the space between trees. It is also important to keep the hedgerow wall open to ensure that sufficient light will penetrate to maintain an 0.5 to 1 m deep cropping mantle or zone. Once trees start cropping, summer pruning is necessary to maintain a fruitful canopy .
In semi-intensive plantings vigorously growing trees produce large water-shoots which, if left, will shade out the fruiting wood. Satisfactory results are obtained when these shoots are removed at a stage when vegetative growth declines in vigour and before the final fruit growth stage starts (that is, mid-January for Golden Queen). The same applies with higher tree densities, but trees require more attention during the summer months. Closer planting forces trees to grow taller and when trees have filled their allotted space, both tree height and width must be controlled. This can be achieved by summer pruning.
Hedgerows lend themselves to mechanical pruning but this only controls the height and width. It must be followed up by detailed pruning to keep the canopy open, by removing upright shoots that shade out the fruiting zone. This practice will also ensure that there are suitable replacement laterals, which are required for cropping in the following year.
In young high-density plantings, trees should be pruned in November, December and mid-January. As the trees become older, shoot growth will be slower and summer pruning may require less effort.
While semi-intensive plantings have proved to be a commercial proposition, less complete information is available on high-density hedgerows. In the first three years of a hedgerow planting at Tatura, the major problems of training and light penetration, which devastated earlier experiments, were overcome by using the summer pruning technique.
Reviewed by Farm Services, August 2013