Healthy soil (and roots) for sustainable blueberry farming

Etienne van Niekerk feeds the soil to feed the plant. It’s a long-term process that promotes biodiversity and healthy soil microorganisms, and builds organic carbon – all secrets to a good blueberry crop for South Cape Fruit. Glenneis Erasmus reports.
Issue date : 06 February 2009

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The Van Greunen brothers have always fostered environmentally friendly production methods on their farms. Situated under the picturesque Outeniqua Mountains outside George, their efforts were taken to a whole new level when Etienne van Niekerk joined them around 1993. For Etienne, the foundation of sustainable production lies in creating a healthy production environment by building both high soil carbon levels and biodiversity. “Many farmers only focus on the soil carbon level,” he explains. “It stimulates microbial life, but it isn’t enough to ensure a desirable diversity of species in a monoculture. Biodiversity improves an ecosystem’s stability and self-sufficiency.” The soil microorganism population in a blueberry monoculture, for example, will be dominated by fungi, but won’t contain enough other beneficial organisms to suppress diseases and pests in the soil food web.

Mileage from compost
But creating a healthy, biodiverse soil environment is much easier said than done. At South Cape Fruit, the company responsible for blueberry production on the Van Greunens’ farms, compost is one of the most important tools for enriching soil carbon and microbial life. The company produces its own aerobic compost from kraal waste, pine shavings and grass. Chicken manure is also added occasionally.
However, it would take huge amounts of compost to build soil carbon levels from the current 2% average to 5%, and the company hit a compost shortage due to the fast replanting programme it followed for the past three years.

Etienne decided the best solution would be to supply compost where it’s most necessary – in the blueberries’ root hair zone. This begins in the nursery when the plants are still young. “It’s much easier and requires less compost to build the soil carbon level above 5% and even up to 10% in a pot, than in the soil outside,” he says. ”According to microbiologist Elaine Ingham, if the microbes don’t have enough nutrients they’ll start utilising the soil’s organic carbon.”

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Cuttings are rooted in peat and transplanted in 2 plant bags in a potting mixture of compost, fine pine bark and sand. Each cutting gets a solution of fulvic acid, kelp and fish emulsion to ensure there’s enough food to feed microbial activity. Fishmeal can be used instead of fish emulsion, but is more difficult to mix into the extract.
If there’s a lack of microbial diversity in the compost, a compost extract from Bio Earth Plant Food is also applied with the fish emulsion. If observation shows individual plants in the nursery need it, they receive extra organic feed, compost extract and foliar sprays.

Planting into orchards
Before it’s transplanted into the orchard at about a year old, each plant is inoculated again with organic feed and compost extract. Some farmers replant cuttings into 5 pots in the nursery before transplanting into orchards, but, says Etienne, “we don’t have enough space in the nurseries and prefer working with small plants – their root systems are much more adaptable and they’re easier to work with than top-heavy plants.”

Before planting, the orchard is ripped and soil is balanced according to a soil analysis. This is the only time the land is physically worked in 10 or 15 years, depending on how long an orchard is kept. Tillage is avoided as far as possible to prevent compaction, which would compromise soil aeration. Compost is applied at a rate of 40m³/ha on the plant ridges, directly in the dripper zone, where soil nutrients are applied via the dripper system.

Etienne explains he’s inoculating the soil when he plants his nursery-treated blueberries with their healthy root systems and rich microbial populations. “The healthy, diverse rhizosphere of the plant, combined with the compost in the dripper zone, works as an umbilical cord which enables the plant to grow for the next two years,” he explains. Effective microorganisms (EM) have also been applied to the orchards via irrigation for the past four years.

Back to the veld
After planting, wild plants and weeds are allowed to grow between rows and on the side of the ridges to increase plant biodiversity and microbial life. Only physical measures – hand slashers – are used to manage the weeds between rows.
“The aim is to allow the area between the ridges to revert back to a more natural state, so blueberries can source nutrients from outside of the dripper zone when they’re mature,” Etienne explains. “We’re not just farming on the ridges; we’re also farming with veld.“

He’s found a difference in the soil pH of the dripper zone, the topsoil and the deeper soil layers between rows: “I think this is a good thing as nutrient availability is better in areas with diverse pH, as long as the pH (water) remains between 4,5 and 6,5,” he stresses.

To mulch or to get a weave?
Ridges are covered with slashed dry grass as an organic mulch, though in some of the new orchards artificial woven fabric is used instead.
“The fabric has been quite efficient in helping to control weeds in the dripper zone,” says Etienne. “Unfortunately, compaction sets in under it and weeds will still grow through the openings where blueberries were planted. These weeds need to be physically removed.”

Etienne adds that soil underneath the fabric can become excessively hot, so he recommends using organic mulch as a buffer between the soil and the fabric.
Weeds are encouraged to grow up from between the ridges over the organic mulch to prevent it from blowing away. The grass is easily controlled with a selective herbicide. Weeds growing through the mulch are cut off with pruning scissors and broad leaf weeds that grow up against blueberry stems are uprooted. Only half as many of the weeds between the rows are still managed with a slasher.
“This improves our energy efficiency and plant growth isn’t disturbed as much, maximising photosynthesis,” Etienne explains.

Old-timer orchards

As they were established without compost, older orchards are managed differently from young ones. Even so, they’ve regularly received organic mulches – now primarily bunch grass – since they were established 10 to 14 years ago. As a result, the top 10cm of the soil has a carbon content of 3,5% while in the deeper layer it’s 1%.
Aside from the organic mulches, all other management practices are chemical. However, biological control replaced chemical pest management four years ago. Chemical weed control is limited to contact herbicides at low concentrations with fulvic acid, a more environmentally friendly option.

Nitrogen released from the organic material has significantly reduced the need for nitrogen applications, to under 50kg/ha per year in the old orchards and under 20kg/ha in the new orchards. This nitrogen is applied primarily as ammonium sulphate, but also as calcium and ammonium nitrate. Applications are always less than 5kg/ha at a time, applied through the dripper system.

Long-term goals
Etienne’s long-term goal is to sustain microbial life at a level where it can efficiently absorb soil nutrients for slow release in plant-available form.
Etienne’s next goal is to improve the biodiversity around the orchards by systematically replacing alien trees with indigenous veld. Plans are also in the pipeline to identify and eliminate or reduce alien weeds in the orchards.
Contact South Cape Fruit on (044) 881 0110.     |fw

Blueberry industry getting cut-throat
The Van Greunens diversified their farming enterprise from diary and vegetable production to include blueberries in 1993. “Farmers at the time could still get away with low production due to these berries’ high premium,” says Bennie van Greunen, who manages pastures and fertilisation. “But with more farmers producing berries and the high capital layout, producers are forced to optimise production methods.”
Sourcing good-quality new cultivars is also a challenge. “You have to keep up with new trends to stay ahead of the market,” says Etienne. “Breeding companies produce new cultivars almost every year.”

The Van Greunens belong to the Eura Fruit Variety Group – the only South African group allowed to cultivate the American Southern Highbush varieties from Florida.
Cultivar choices are limited by the production area’s mild climatic conditions, as certain Southern Highbush cultivars have a high winter chill demand. “We’ve paid vast ‘school fees’ to find the best cultivars for our conditions, and we’re still on a learning curve,” Etienne admits.