Selecting varieties for commercial macadamia orchards

Selecting varieties for commercial orchards is a complicated process for many growers and nurseries. There are many varieties to choose from, with each responding differently to different climates, regions, orchard and water management.

Our expert team at RedSun Hortitech have put a few suggestions together to assist in the process of selecting varieties for commercial plantations.

 

Think in terms of the first-grade kernel per hectare

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 back on farm. Yield first grade kernel (kg) = Yield NIS (kg) x sound kernel recovery (SKR %) x first grade (%).

Tree yields can be misleading if taken in isolation because, in the end, this is driven by income per hectare. A variety may have a high yield per tree, but if the trees have low spacing and are excessively large, they may still perform poorly when assessed on a per hectare basis. Equally, small structured trees planted on a wide spacing will 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

All factors must be considered when making decisions about new orchards, such as yield benchmarks, climatic influence, management capacity and equipment to be used.  Yield, income, cost, profit etc. must all be managed and converted to a per hectare basis in order to drive planning and management decisions. 

 

Decide on planting density

From our perspective, the first step in this process is to decide on the tree density you intend to plant, which is led by climate and variety. There is an almost unlimited range of planting densities to choose from. Some examples include:

  • Low density – 10 m x 5 m (200 tree/ha)
  • Medium density – 8 m x 4m (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 in Southern Africa are planted at medium densities (312 @ 8×4).

In general, a low-density orchard will take much longer to reach full production, because the trees will take many years to completely cover the open and non-productive orchard floor. The large trees will also require more extensive equipment to manage them in the long term.

High-density orchards have higher setup costs per hectare and require more intensive management, such as pruning sooner in the life span of the orchard. However, it has the benefit of reaching full production much sooner. An orchard planted at 1 000 trees per hectare can achieve 5 tons per hectare in 6 – 7 years, whereas a low-density orchard that has 200 trees per hectare may take 12- 20 years to achieve the same result.  Low and high-density orchards should eventually achieve similar maximum yields per hectare per annum, but there are still some questions as to whether high-density orchards can maintain these yields in the long term. To get the full benefit of early returns from high density orchards, we need to select precocious varieties.

The planting density of a new orchard will influence the selection of varieties. It is unlikely that a semi-dwarfing, small, compact upright tree like the A16 or 814 varieties will fill the orchard at low densities, leaving large areas of the orchard unproductive with lower returns/ha. By the same token, planting a larger precocious variety, such as 695, 842, and 849, at high densities would mean intensive canopy management is required early on to keep the orchard under control in later years.

 

Importance of various traits

When selecting varieties, it is essential to take all the different traits of each variety into account, rather than concentrating on one or two. To a degree, the importance that is placed on various traits is a subjective decision and depends on the mix of climate and varieties being considered.  Growers have to understand the traits of various varieties available in order to make the necessary decisions for the long term.

Some varieties are more susceptible to heat stress; for example, the A4 variety, is a very precocious tree that can 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 mid-season nut drop. However, it is more susceptible to stress from high temperatures but performs well in milder regions. The A4 variety needs a different nutritional program to match the demands the orchard has to compensate for its early cropping ability. In contrast, A16 is a slow-growing and wind tolerant variety but is a high yielder with excellent nut quality and would achieve high yields (and returns) per hectare if planted at higher densities.  Likewise, this will require a significantly different nutritional program to match the stage of orchard development over time as well as higher planting 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 flowering and tree stress risk and to minimise the need for additional large capital processing and storage equipment to handle the harvest volume. Another vital aspect to consider is to select varieties that present the same tree size, more or less, across orchards.  Aside from nut bearing consistency, achieving efficiency in management of orchard cycles such as pruning, spraying, nutrition and irrigation.

While kernel characters are important, any variety that has been commercialised will have acceptable kernel qualities in terms of flavor and appearance. Of course, there is ongoing debate around whether small or large kernels are more desirable. Some processors generally prefer large kernels, because they are less costly to handle, simply because there are less of them for any given weight. Others prefer small kernels for confectionary and catering etc. Growers need to ensure that the varieties chosen  have a larger percentage of wholes which attract a premium

 

Design and plant the orchard according to polliniser compatibility

Pollen compatibilities have gained prominence in recent years, however, there is still more work to be done before its importance can be quantified. To date, the trials have been based on raceme by raceme tests and designed to highlight different compatibilities. There is very limited data on actual orchard situations. For these reasons, this data should be given lower priority in selecting varieties, but a high priority when determining an orchard’s design.

It is recommended to select at least three varieties. This reduces the risk of varieties not performing to expectations. This also creates the potential for maximising pollination overlaps and extends the flowering and harvest periods. 

Once varieties have been selected, growers must design the orchard in a way that will maximise cross-pollination by planting the most compatible variety combinations in proximity to one another based on flowering patterns.

It is recommended that complete blocks of a certain variety are planted, rather than mixing the varieties in the row. While this may slightly reduce pollination, it will make orchards easier to manage. Beekeeping activities may also promote pollination over the flowering periods.

Selecting varieties is dependent on so many different factors, which is why at Red Sun Hortitech we work with you, as the grower, to find the perfect combination of varieties to suit your needs, climate and region. We aim to support you in growing a successful macadamia orchard with the best possible yields.

 

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