The pros and cons of low- and high-density tree planting. By Grethe Bestbier.
When Anton Müller, technical manager of Kromco, visited Italy ten years ago, he came back with quite a few things to rethink. While explaining why, in South Africa, we believe it is so important to plant 4×1.5m, he was challenged by an Italian farmer. “You know what,” the farmer said, “You grow your area full, but I plant my area full.” This prompted Müller to re-examine why we plant at such low density, and whether it really is the best for crop production.
Asking the questions that matter
There are many questions regarding South African farmers growing their areas full, instead of planting more trees. Most importantly, why do we do this? Müller believes that the cost of nursery trees is the main reason for our choice of low-density planting.
“As you know, everything costs money, so in the words of William Shakespeare, ‘To buy trees, or not to buy – that is the question’,” joked Müller.
After his return from Italy, Müller looked into studies that link tree numbers with crop production. He found that in various cases, more trees lead to a much higher crop accumulation.
Müller realised that a fundamental question was what exactly the prerequisite is for a successful orchard. He wanted to discover how this links to tree numbers and planting density. Maybe then he could find out whether growing our areas full, like we do in South Africa, really is the best choice.
Müller learned that the number one prerequisite is reaching optimal light interception as quickly as possible. For perennial crops, it is also important to maintain the maximum light distribution as time passes. This requires keeping a high ratio of surface area to volume. Thinner and more rectangular trees have better light distribution than wider and more spherical trees.
The evolution of tree planting
According to Müller, the good old days were characterised by very wide planting. Growers relied on heading cuts, with trees tending to develop strong structural branches over time. The final tree often formed a half-sphere, known for a weak ratio of surface area to volume, and poor light distribution.
“Over the long term, their complex light distribution management required Solomon’s wisdom and Job’s patience,” said Müller.
The current standard is to plant 4×1.5m. For these trees, growers often choose a management approach similar to wide systems.
“You start off with roughly a 1.5m to 1.8m tree, and in most cases, people pat themselves on the back when they reach 80% of row width,” said Müller, referring to tree height. “You also end with a tree with a lot of permanent structures, but the tree is more rectangular.”
Not only do the thinly shaped trees experience better light distribution, but production is increased.
“Way back, everyone referred to the maximum crop of about 60 tonnes per hectare,” said Müller. “Everyone is now in the 100-tonnes club.”
Although income increased, it has reached a plateau. Looking at industry comparisons, the past ten years are characterised by an income of about R200 000 to R250 000 per hectare. However, inflation doesn’t stand still, and breaking this ceiling is an important objective.
Planting for the future
“The future will be innovative,” said Müller. “Standard trees will be planted closer together.” He envisages row spacing of 3.5 to 3.0 metres.
According to Müller, we will see more double leader, Guyot, double spindle, and V-structured systems, and early cropping with much higher pack-out of South African standards. The adoption of simpler systems will also simply instructions to employees.
“I also believe there will be an increased income per hectare, efficiency and profitability,” Müller added.
Müller modelled the sensitivity of net present value to tree price and crop quality for orchards planted at different densities. According to his calculations, the impact of tree price on net present value in high-tonnage orchards is less than 2.5%. “Get the best tree quality, even if the cost is shocking,” he stressed.
When considering quality, Müller pointed out that it’s not surprising that growers with orchards that have low establishment costs only focus on tonnes per hectare. “It’s possible, from an economic point of view, to have a successful orchard with low-quality but high tonnages.”
In conclusion, Müller emphasised that saving money on trees is a false economy. “Do not save money on the early management of that orchard — spend time on your orchard design if you are serious on increasing fruit quality,” he said, “because whether you buy more trees or not, you are going to pay for them.”