Mechanical harvesting and the super high-density orchard system could be the solution to the olive-oil industry’s high labour costs. This system prunes and harvests olives mechanically, achieving sustainable high annual yields and producing premium quality extra-virgin olive oil.

ARC researcher and olive expert Carlo Costa spoke to Denene Erasmus about the opportunities and challenges of this system for local olive producers.

Olive production is highly labour-intensive, especially in countries like South Africa, where most olives are still harvested by hand.

Labour costs have a significant impact on the price of olive oil, and if they increase it could raise the price of this already expensive product. Harvesting olives mechanically in super-high-density (SHD) orchards may be the solution.

The SHD olive orchard system

The key factors of the SHD system are the choice of olive cultivar, the right tree-planting, -pruning and -training system, and using straddle harvesters.

The system allows for continual and efficient harvesting of olives, using modified grape harvesters at a rate of about 6t/hour of fruit. With these machines, fruit can be harvested at optimal ripeness with little damage to it or the trees.

Trees from low-vigour cultivars are planted at high density and trained to an upright central leader on a trellis system. This lets orchards come into bearing quickly, with high, regular and sustainable annual yields.

Trees can be pruned mechanically by hedging and topping, further cutting labour costs. Fruit can be directly transferred from the tree to the press, for premium quality extra-virgin olive oil.

The concept was developed in Spain some 20 years ago by Agromillora, an international nursery specialising in propagation and marketing stone fruit, grapevine and olive rootstocks.

Today, over 100 000ha of olives have been planted to SHD worldwide. Jordi Mateu, a director of Agromillora, spoke about his experience with SHD plantings at the SA National Olive Conference held during the Agri Cape Week recently.

To date they have achieved 100% machine harvesting (up to 98% of fruit is removed, requiring no further intervention), at a rate of 2hr/ha.

An average production of 3t/ha to 4t/ha is obtained in the third year and a sustainable annual production of 10t/ha to 12t/ha from year six.

Jordi says that traditional olive growing areas in Europe may well be reduced when the current subsidy arrangement between farmers and the state changes in 2013.

This will give a country such as South Africa the opportunity to become a bigger player in the extra-virgin olive oil industry. 

More research needed

Carlo Costa is a local olive expert, a researcher in the horticulture division of the Agricultural Research Council (ARC) at Infruitec in Stellenbosch, and author of the definitive study, Olive Production in South Africa: A Handbook for Olive Growers.

“Although I’m confident this SHD system will be the solution to more efficient and cost-effective olive harvesting, there are still a few questions that need answering,” he says.

Researchers have yet to determine the productive lifetime or most efficient pruning system for this type of orchard.

“We also need to expand the range of cultivars suited to this system, since mill capacity demands high investment and could be a limiting factor,” says Carlo.

“I foresee a shift in the season, where harvesting is done earlier in the hotter part of the year, where early morning harvesting or possibly even night harvesting may become common.”
Choosing the right cultivar

Currently, ARC Infruitec-Nietvoorbij, through the NRF, is collaborating with olive-breeding programmes in Europe to find improved selections to extend the season. A suitable cultivar choice is crucial for best results with the SHD system.

“The variety must have relatively low vigor. Trees have to start bearing within three years of planting,” says Carlo. “These two factors influence one another – when a tree uses more energy to produce fruit, it will have less energy available for vegetative growth.”

The trees should have a low tendency towards alternate bearing. The branching habit must be soft and flexible but still tough, instead of being brittle.

“It’s not easy to get appropriate varieties,” he adds. “We have finished tests on three that were found suitable for the system under South African growing conditions, and are testing three newer cultivars. The three approved are a Koroneiki clone, an Arbequina clone and an Arbosana clone.”

Tree planting, pruning and training system

SHD orchards have to be harvested according to specification: between 1 600 trees/ha and 2 100 trees/ha, spaced at 1,35m to 1,5m between the trees and 3,5m to 4m between the rows, and topped to a height of about 2,5m.

“The trees must be pruned systematically to keep within their allotted growing spaces and to allow effective light penetration. Correctly managed trees remain productive for a relatively long economic lifetime,” says Carlo. “In California, producers combine a pruning rotation with mechanical hedge trimming.

“If trees become too dense and large for mechanical pruning, manual intervention will be required. After 15 to 20 years, when yields start declining, the trees may need major regeneration. This means establishing a new leader, but that’s no problem because an olive tree can renew itself.”

Tree volume must be limited to specific dimensions, since light needs to penetrate the canopy for maximum fruit production and oil accumulation. Effective light reaches a maximum depth of 0,75m, therefore a tree width of 1,5m is optimal.

Systems attempting to use larger trees and wider spacings will be less efficient.

Harvesting machine

The system was designed to use standard wine-grape straddle harvesters with only slight modifications for olives.

“I was amazed when I saw this kind of harvesting for the first time in 2002,” says Carlo. “When all the components of the SHD system are in place, these mechanical harvesters work very well without damaging either the fruit or the trees, and almost no fruit drops to the ground.”

However, when machines are not set up correctly, or when trees are improperly pruned or when the operator is in a hurry, some damage and losses can occur.

Orchard management practices

“Efficient irrigation and nutrition, preferably through fertigation, is extremely important,” stresses Carlo. “In the early stages, continual growth and control of the upright leader as well as sufficient lateral growth is important. It will remain so throughout the orchard’s lifetime, ensuring sufficient and regular crop and bearing wood production.”

As with any intensive fruit production system, good soil management practice, including mulching, weed control and cover crops in the alleyway are necessary to reduce compaction and create the right environment for healthy root growth.

“During early growth, pest and disease control is critical as the tree can’t afford to lose the dominance of the leader,” says Carlo. “The olive beetle can severely damage the future shape of the tree.

At such a high tree density, measures preventing fungal diseases, such as olive leaf spot and anthracnosis, must be in place. Correct irrigation scheduling reduces the incidence of root-borne disease pathogens such as anthracnose.

The right irrigation scheduling is also important to reduce the chance of root-borne pathogens like Phytophthora and Pythium.

Economic viability

Carlo is adamant that an SHD system is a cost-effective option, despite the high establishment cost and capital investment in machinery and infrastructure.

“The harvester is very expensive, but we foresee growers harvesting fruit on contract,” says Carlo. “The orchards, with many trees per hectare, will also be expensive to establish as they will have to trellised.

“Growers should stake olive trees in most orchard situations, and a substantial stake at every tree in a relatively high-density orchard is more expensive than a trellis system. But at a higher density, you also get a faster return on your investment.”

Facing challenges

“Growers must be prepared to learn as they go along. The system is new, and more research is needed on cultivars and production practices,” says Carlo.

“The industry should support this. It will need fine-tuning by growers to optimise production and get a good lifespan out of the orchard. I’m convinced that all the benefits the system offers will make it worth the risk. 

“At the moment, the biggest challenge facing South African olive growers is the need to educate consumers. There has to be a stronger marketing drive to show the benefits of using premium quality extra-virgin olive oil products.”

Contact Carlo Costa at  costac@arc.agric.za.