06 April 2018 Read: 108
Selecting macadamia varieties to plant in commercial orchards is a complicated and subjective challenge for growers and nurseries as performance varies from region to region and there is no perfect variety for all climatic and management conditions, says Managing Director of Red Sun Hortitech, Mark Hassenkamp. Having dedicated clonal mother blocks for propagation of all commercial South African macadamia varieties, RedSun is approved by CitroGold to propagate and distribute Australian Hidden Valley macadamia varieties to Southern African growers. Experts at the company suggest factors such as yield benchmarks, climate, management capacity, equipment, and most importantly, yield, income, cost and profit per hectare must be considered as decision making drivers.
Think in terms of First Grade kernel per hectare Many comparisons between varieties report yield of nut in shell (NIS) per tree, but this is in general a poor measure of tree performance, they say. Growers are effectively paid for first grade kernel free of rejects. Yield of first grade kernel is the measure that is most closely related to income. Yield first grade kernel (kg) = Yield NIS (kg) x sound kernel recovery (SKR %) x first grade (%). A variety may have a high yield per tree, but if trees have a low spacing and are excessively large they may still perform poorly when assessed on a per hectare basis. Equally, small trees planted on a wide spacing will also not achieve acceptable yields per hectare. Yield first grade kernel per hectare (kg) = first grade kernel per tree (kg) x trees per hectare = first grade kernel per tree(kg) x 10 000 / between row width / within row width where trees will fit at nominated trees/ha.
Decide on planting density.
The first question should be what tree density is intended for the orchard and that is informed by climate and variety.
There is an almost unlimited range to choose from, for example:
- Low density – 10 m x 5 m (200 tree/ha)
- Medium density – 8 mx4m (312 tree/ha)
- Medium-high density – 7 m x 3 m (476 tree/ha)
- High density – 5 m x 2 m (1 000 tree/ha)
Most new orchards are planted at medium densities (312 @ 8x4).
It is unlikely that a semi-dwarfing, small, compact upright tree like A16 will fill the orchard at low densities, leaving a large area of the orchard unproductive with lower returns per hectare. Similarly, planting a larger precocious variety such as 695, 842, and 849 at high densities would mean intensive management to keep the orchard under control in later years.
Hidden Valley macadamia varieties which are defined by an A prefix are assessed on their ability to produce high first grade kernel yields per hectare. In general, Hassenkamp says, they were selected with a preference for medium to small size trees suitable for medium to high planting densities to improve total returns per ha.
Importance of various traits To a degree the importance placed on various traits is a subjective decision and will also depend on the mix of climate and varieties under consideration. Some varieties are more heat stress susceptible. For example, another Australian selection, A4 is a very precocious able to produce commercial yields in three years. It has a medium spreading tree shape with an open willowy canopy susceptible to wind damage. It has excellent quality and size kernel with a midseason nut drop. It is however more susceptible to stress from high temperatures but performs well in milder regions, A4 needs extra fertilizer to compensate for its early cropping ability. In contrast, A16 is a slow growing and wind tolerant variety but a high yielder with excellent nut quality and would achieve high yields, and returns per hectare, if the trees are planted at higher densities.
Many growers consider it desirable to have all varieties ready for harvest at the same time, to achieve a short harvest window. Other growers prefer to spread the harvest out to reduce stress risk and minimise the need for large capital equipment to handle the harvest. Another important aspect to consider is to select varieties that are more or less the same tree size across orchards.
Hassenkamp says while kernel characters are important, in general, any commercialised variety will have acceptable kernel qualities related to flavour and appearance. Although, there are some debates at the moment as to whether small or large kernels are more desirable. “Processors prefer large kernels, because they are less costly to handle, simply because there are less of them for any given weight”. Others may prefer small kernels for confectionary chocolate coating for example.
“If a grower chooses this option, they must guarantee the variety has a larger percentage of whole kernels, rather than small halves which are more expensive for processors to sort,” Hassenkamp says.
Pollen compatibilities have also gained prominence in recent years. However, there is still more work to be done before its importance can be exactly determined.
Design and plant the orchard according to polleniser compatibility. Select at least three varieties to reduce the risk of varieties not performing up to expectations. It creates the potential to maximise pollination. It extends the flowering and harvest periods. And, once varieties are selected, the grower should design the orchard in such a way to maximise cross pollination – plan-ting the most compatible combinations close to one another, Hassenkamp says. “Keep flowering periods in mind as well. We recommend solid blocks of a certain variety should be planted.”
Red Sun currently has two experimental varieties on controlled release namely A203 which has a medium to large uneven sized nut with white kernels which drop mid-season. The variety is hardy and may suit more marginal areas and A268, a medium to large tree with an open spreading canopy, a mid-season nut drop and very large, good quality nuts which have creamy, white kernels. It appears to be hardy and may do well in cooler regions, however whether or not the tree is frost tolerant has yet to be determined.