Apple growing trends today are to produce small trees that begin to bear fruit in the second year. Varieties are grown on dwarf rootstocks, about 2m tall, planted closer together. In 1990 at Orange, Hi Early Delicious on M.9, M.26 and M.27 rootstocks were planted in one (1667 trees/ha), two (2286 trees/ha), three (3043 trees/ha) and four (2822 trees/ha) row bed systems. Yields by year five have reached 50-70 tonnes/ha with high quality fruit. M.27 are the smallest, then M.9, then M.26. Shading within the beds has been no problem, but less highly coloured varieties may produce less colour.
Twenty to thirty years ago, apple tree density was 250-300 trees/ha and the trees first carried fruit by the fifth or sixth year. Introduction of new growing methods such as medium density planting (8-900 trees/ha), more dwarfing rootstocks (MM.106 and Northern Spy), and central leader pruning has significantly influenced the capacity of the apple industry to remain profitable under pressures from cost of production increases. A logical further stage in industry development is the intensification of production using higher density plantings which will also allow more cost effective hail damage protection and use of irrigation.
High density planting of apples on dwarf rootstocks (M.9 and M.26) in beds was developed in Holland in the 1970s. Trees on these dwarf rootstocks grow to about 2m high and begin to carry a crop in the second year. Overseas results have shown that tree densities of 2000 trees/ha up to 5000 trees/ha lead to higher yields per hectare and a higher percentage of fruit that is of good quality, e.g. large, well coloured and more uniform in size and maturity. These systems have been developed for use in other parts of the world especially Europe and Canada. Adjustments to cultural systems have been necessary including new pruning techniques, cultivars and planting systems. New orchard machinery has been developed to cope with the changes in orchard design. In Holland there are a large number of multiple row commercial orchards and in the United Kingdom there are many two or three row orchards (1993).
These systems have not been developed for the high light intensity situations found in Australian apple growing areas where 25% of total light is required for good colour and size compared with 50% for the 43 to 56° latitudes in the northern hemisphere. High light intensities of lower latitudes have been shown to produce higher yields than in higher latitudes. Our pressures on land are not yet as great as in Europe but efficiency of production is very high on the priority list.
The main aim of this trial was to see what system might be best under our high light intensity conditions in Australia. High density plantation systems had been developed extensively in Holland and now in other parts of Europe including the U.K. are in general use especially two and three row beds. Developments in the northern hemisphere are at latitudes of about 42 to 55°. In Australia, the latitudes are between 33 and 40° and light is of much higher intensity, fruit requiring only 25% at least of total light to produce good size and quality, compared to closer to 50% total light in higher latitudes. Higher light intensities have been shown to increase apple production.
Now this is already starting to occur, and will provide the basis for consistent supply of a high quality product to markets. The more intensive closer planted orchards that are progressively replacing the traditional wide-spaced trees (15 -17 t/ha) yield upwards of 30 tonnes per hectare, with the potential to yield between 50 and 100 tonnes per hectare. High density systems have the potential to increase yield to 100 tonnes/ha. The higher density with smaller trees will allow better light penetration. This in turn should produce a higher proportion of good quality apples with less wastage of small poor coloured fruit.
The Hi Early Delicious trees were planted in 1990 at Orange Agricultural Research and Veterinary Centre. They were worked on the dwarf rootstocks, M.9, M.26 and M.27, and planted in beds of 1, 2, 3 and 4 rows, at 1667, 2286, 3043 and 2822 trees/ha respectively. At the same time standard trees on MM.106 were planted in single rows for comparison at 880 trees/ha. The trees on dwarf rootstocks are pruned as spindles, compared with current MM. 106 trees as commercial central leaders. Each bed is about 75 sq.m depending on tree density with alleys of 4m wide. The alley can be narrower in a commercial planting at 3.5 or even 3m wide, provided the tractor is small and has a narrow wheel base. The planting systems and the spacing of trees are shown in Figure 1.
This project is becoming well established after planting in 1990, with trees on M.9 and M.26 particularly producing excellent fruit quality and the yields are still increasing. Tree size remains in the order of smallest to largest, M.27, M.9, M.26 and MM.106 with these rootstocks (Table 1).
Table 1. Tree size as Butt Circumference (cm)
There is need already to limit tree height on M.9 and M.26 to a side branch. Where the growth of the terminal shoot has grown too vigorously, it can be cut out to a weaker side branch. In years 3 and 4, the terminal shoot can be slowed down by bending it unpruned (see below) and this will also encourage flower bud formation along the shoot. This was not done on these trees at that time, but looking back now on tree vigour of M. 9 and M.26, it would probably have been worthwhile.
The project has become established after planting in 1990. Fruit has been harvested from 1992 to 1995. So far there have been no signs of overcrowding with any density system. Trees on M.27 are appearing to be too dwarfing for adequate production of quality fruit, also fruit size tends to be smaller than that growing on M.9 or M .26.
The yields per hectare (Table 2) in 1995 were similar on M.9 and M.26 with greater yields the higher the tree density, three row and four row being much the same. The yields on M.27 and MM.106 were much lower, but the more rows per bed increasing yields up to the higher density with M.27. Accumulated yields (in brackets) followed a similar pattern, and the accumulated yields per year are shown in figure 2. Yields by year five have reached 50-70 tonnes/ha with high quality fruit. Fruit weight and number per bed are steadily increasing (Fig. 4) and have not reached a plateau yet. The standard trees on MM.106 have a long way to go. In Figure 3, fruit weight and number in 1995 are similar but fruit numbers from M.27 trees are higher in relation to weight.
Table 2. The yields of the different bed systems in tonnes/hectare in 1995 (Accumulated yield 1922-95).
| Rootstock | 1667 tr/ha | 2286 tr/ha | 3043 tr/ha | 2822 tr/ha |
| M 9 | ||||
| M.26 | ||||
| M.27 | ||||
| MM 106 |
Fruit size has not been affected by tree density so far, but rootstocks have affected fruit size. The yields of M.9 and M.26 had a higher proportion of large fruit than M.27 or MM.106. Hi Early being a highly coloured striped red cultivar of Delicious has, so far, shown no sign of colour reduction in the higher density beds or elsewhere.
Fruit size showed a trend to more large fruit than small on the multiple row beds with little difference between trees on M.9 or M.26 (Table 3). Trees on M.27 had more small fruit on the systems than M.9, M.26 or MM.106. Hi Early being a highly coloured striped red cultivar of Delicious has, so far, shown no sign of colour reduction in the higher density beds or elsewhere. Ordinary Gala did show sign of less red colour within the middle of the three and four row beds on the lower branches.
Sunburn on apples can occur when temperatures exceed 30°C, but foliage can protect the fruit. Sunburn was particularly obvious on the trees on M.27, whichever system. The rootstock M .27 is also too weak in growth to fully occupy the space allowed with Hi Early Delicious and they did not have enough foliage on top to protect the fruit from sunburn. Table 3. The Percent of small fruit and large fruit in each bed system in 1995
| Rootstock | 1667 tr/ha | 2286 tr/ha | 3043 tr/ha | 2822 t /ha | ||||
| M.9 | ||||||||
| M.26 | ||||||||
| M.27 | ||||||||
| MM.106 | ||||||||
| 880 tr/ha | ||||||||
M.27 rootstock may be still useful with a more vigorous cultivar such as Jonagold on new apple soil. If longer stakes had been used with two metres above the ground combined with closer planting, the M. 27 trees could have been trained taller and have maybe been more efficient. After this trial was planted, I saw in Europe that longer stakes were already being used. M.27 would appear to be more efficient when growing triploid varieties such as Jonagold and Mutsu, which have more inherent vigour, growth and larger leaf and fruit size.
Without having specialized equipment for the application of herbicide in the multiple row beds, there were problems with weed control in the two higher densities. The spreading of straw mulch (70-l00mm deep) across the beds has helped control weeds much more efficiently. Also, even during the driest parts of a such a dry season at least, there was usually some moisture just below the straw, away from where the drippers were. The odd weed that got away, grew large and did need removal, or a spot spray. Now all beds have a straw mulch.
Pest and disease control with spraying is no problem for tree cover. In Europe where these systems have been practised over 20-25 year, equipment has been developed to cope with such problems. The mulch will also improve soil structure and worm numbers.
Some of the assets that could come from this work are:
The information from this trial should be valuable to the apple industry in the future.
Figure 2
Figure 3
Figure 4
Figure 5
