Soil that is in tip-top condition results in healthier plants, which should require less intervention over time to keep them producing optimally. With this in mind, Johan Swanepoel, who farms macadamias near Barberton, Mpumalanga, has made a significant investment in his soil.

“Healthy soil and roots mean healthy trees. This means that no shortcuts can be taken
when you do your land preparation before establishing your orchard. It also means
there needs to be a continuous investment in the soil to build it up over time,” he says.

Swanepoel is new to macadamia farming but not soil health. His main business is Earth2Earth Organics, a compost production company based in Limpopo and Mpumalanga. He has seen at first hand the effect that compost has had on his customers’ farms, so when it came time to establish his own orchards, this was a dominant factor.

Swanepoel has 250ha of macadamias, ranging from three-month-old trees to some that are seven years old. The seven-year-old trees, covering 8ha, were obtained last year when he bought an adjacent farm. He had his first harvest this year.

“The orchards were severely neglected, and we are in the process of getting the trees in optimal shape by adding compost, pruning the trees, and providing proper irrigation. We only achieved 1,5t/ha on these trees, with a 34% sound kernel recovery. We should get a better indication of what the potential of this orchard is next year, after the trees have gone through a season of optimal care.”

With the bulk of Swanepoel’s trees not yet in full production, calculating the effect of his investment in the soil is difficult. But he has no doubts that he will reap the rewards of his efforts.

The right foundation

Land preparation starts with clearing the land with a bulldozer. The entire field is then ripped to a depth of 750mm to 800mm. This is deeper than the standard rip of 600mm to ensure that the soil is as loose as possible.

Ridges are made and compost is strewn in the planting rows using a spreader at a rate of between 10t/ha and 15t/ha. These rows are then ripped again to mix the compost into the soil.

The ridges are important for water management and root health: “We have a lot of slopes on the farm, and by making ridges that run horizontally across the slopes, water run-off and erosion are reduced.

“In the macadamia industry, there is a notion that trees planted in a north-south direction have better yields. But you can’t ignore the impact of slopes and water run-off. I’ve seen orchards planted in an east-west direction that produce just as well – it comes down to water management. Rainwater has a better chance to seep into the ground if the flow is blocked by ridges. Likewise, if ridges run vertically down the hill, rainwater will erode the soil,” says Swanepoel.

The ridges also serve to lift the roots out of the water in incidents where there has been a lot of rain. Roots submerged in water can develop fungal diseases and place the trees under stress.

Once the trees have been planted, wood chips are placed around their trunks as mulch to aid moisture retention in the soil. Since the wood chips decompose over time, they add an additional compost application. Cover crops are not planted, since natural grasses are prolific, emerging shortly after the orchards have been established and covering the soil.

To protect young trees from the sun and insect damage, the trunks are painted with a water-based paint mixed with insecticide. Copper is applied to protect the trees against any fungal infections, such as those caused by Phytophthora.

Hennie Botha, Swanepoel’s farm manager, says the paint is necessary to protect the trunks from harsh sunlight since the trees have few leaves. The insecticide wards off ants, which can also damage the trees.

“Younger trees are not necessarily more prone to fungal diseases and insect damage, but if you protect trees from an early stage, they become stronger over time because they have never been under any stress,” says Botha.

It’s what you put in

Swanepoel’s compost is made up of 20% cattle manure, 10% charcoal fines, and the rest is pine bark. The latter is abundantly available in Limpopo and Mpumalanga from the forestry industry and has a higher moisture retention effect on the soil than other wood bark.

Once mixed, the compost is formed into rows and left to decompose for at least eight months. During this time, the piles are rotated at least six times and the mixture regularly irrigated. Moisture is important to help break down the material, keep the microbes healthy, and leach out any heavy metals that have come from the manure.

Swanepoel emphasises that the benefits of compost are only gained once the material has decomposed. “But all compost is not equal and it must be tested in a laboratory to get an indication of the nutrients. One can’t just assume that any compost mixture will have the right mix of microbes and nutrients and that it will benefit the plants.”

The compost has its own population of beneficial microbes that aid soil health, but it acts more as a medium to create a favourable environment for microbes already present in the soil.

“When the soil environment is at its optimum, the microbe population quickly increases, working to make nutrients available to plant roots,” Swanepoel says. Applying compost is a continuous activity, since the material breaks down over time.

“The more microbes in the soil, the faster the compost is broken down and the nutrients absorbed by the trees. This is why new layers of compost need to be added every year.”

He starts with an application of 2t/ha on newly established trees, going up to 5t/ha on older trees. Compost is applied with a spreader.

“Adding it directly under the tree is ideal, but this would require time-consuming and labour-intensive manual applications.”

Fertiliser applications are done according to the orchards’ needs, based on soil analysis. Swanepoel however believes that over time, as soil health increases, inputs will be reduced.

“The ultimate goal is to cut our nutrient inputs by half. I have seen this happen on cash-crop farms where compost is applied liberally, but we are still trying to figure out what a feasible percentage would be on macadamias.

“Applying sufficient amounts of compost is expensive – mostly because of the transport cost – which has deterred many macadamia farmers from going this route. In Limpopo, there is hardly an avocado farmer that is not using compost, which tells me that there are benefits. But we still need to make this mind shift in the macadamia industry to make the investment,” he says.

Reaping the benefits

Swanepoel’s faith in compost is very much based on results he has observed on the cash-crop farms in Limpopo that he supplies with compost.

“These are mega-farmers who wouldn’t be making such substantial investments in compost if it wasn’t worth it. Of course, with a cash crop like tomatoes, for example, the effect is more immediate because the plant roots are shorter. For macadamias, we are only likely to start reaping the rewards after year five. The investment is worth it because healthier roots produce healthier trees, which produce more, and better quality nuts.”

Water savings

A more immediate benefit of compost applications is water savings, which also impact a farm’s total electricity bill.

Swanepoel has reduced his water requirement by between 18% and 20% through compost applications, since soil moisture is better retained.

“We don’t have a lot of water on this farm, so we need to carefully manage our resources. We’ve opted for low-flow drip irrigation, the water for which is gravity fed to minimise electricity usage. Water is applied in three cycles per week, with only one cycle of three hours per day on irrigation days. Since tree roots typically extend to a maximum depth of 900mm, it is a waste to have water flow beyond that point. This is why it is important to manage the cycle length.”

Exactly how much water macadamias require is a question with which the industry is still grappling. Swanepoel’s conversations with other macadamia farmers have yielded mixed results, which is why he is now conducting his own trials.

“At this stage it seems 100ℓ per tree per week in spring and summer is sufficient.”

With water scarcity being front of mind, Swanepoel doesn’t gamble with soil moisture. “Technology like soil moisture probes is useful to determine the optimal irrigation times and lengths, but it’s vital that we don’t take chances. We therefore have areas in the orchards where we physically dig holes to see if the moisture levels are adequate before scheduling our irrigation.”

Making optimal use of every drop of water, Swanepoel believes in the value of low-flow drip irrigation, which places the water directly on the ground, below the mulch layer. This means wind does not blow the water away, as could be the case with micro irrigation, and the mulch protects the water from evaporation.

The mulch also plays another important role: preventing soil compaction. “Raindrops can compact soil far more than tractors do. This is why mulch is important for protecting your soil, because it takes the ‘hit’ from the raindrops and gently disperses water into the soil.”

Reducing input costs requires a significant initial investment in inputs that increase soil and orchard health. With mounting evidence of the benefits of compost for plant health, Swanepoel’s investment is set to pay off for years to come.