A new agricultural revolution

The focus shifts to sustainability. By Anna Mouton.

Agricultural production has grown exponentially for nearly two centuries. Outputs more than tripled in the period 1960–2015 — the achievements of the so-called Green Revolution of the 1960s are so significant that they earned one of its founders the Nobel Peace Prize.

Science has given us synthetic fertilisers, fungicides, pesticides, weedkillers, and other agrochemicals. Advances in areas such as irrigation, mechanisation, and genetics have all contributed to the rise of industrial agriculture. The result is that agriculture has managed to keep feeding us as the world population swells inexorably to 8 billion people.

But can we trust that our current resource-intensive way of farming will continue to deliver results? Or are we amassing a mounting environmental debt?

The focus of agriculture is slowly shifting from the present to the future, with an increased emphasis on stewardship and sustainability. Fresh Quarterly spoke to some of the people at the forefront of this movement, to learn about new approaches to orchard management, and to ask why spending on soil health is a sound investment.

Future-focussed farming

The sustainability of a business is about more than ecological sustainability, says Hendrik Pohl, production manager at Bokveldskloof in Ceres. “We must be economically sustainable, we must fulfil our social contract, and we must leave our resource in a better condition than we received it. From a production perspective, the focus is on soil health.”

Pohl is speaking to a common criticism of modern agriculture — the perception that intensive farming is destroying soil health. Soil health means different things to different people, but most growers would agree that healthy soils are those that support long-term agricultural productivity. Healthy soils also support natural ecosystems, promote biodiversity, and sequester carbon.

“I don’t like the term soil health,” says Angelique Pretorius, soil scientist and technical manager at Kromco, “because how do you define an unhealthy soil?” She thinks that soil fertility is the more scientifically correct term because there are norms for soil fertility in the context of specific commodities. Soil health, on the other hand, is not sufficiently defined.

“I prefer the term sustainable — that includes safeguarding your soils for the next generation,” states Pretorius. “But it also means farming profitably and in cooperation with the environment.” Farming sustainably is about balancing the urgency of the harvest this season with the importance of harvests in years to come.

“Everything we do now has an impact in 20–30 years,” reflects Ian Cunningham, head of production at Fine Farms in Elgin. “We’re custodians of the land for a short period in the grand scheme of things.”

Cunningham sees the sustainability shift as a recalibration to some of the tried-and-tested methods used by previous generations. The time is ripe to take another look at pre-industrial customs such as composting and mulching — provided they make financial sense.

“The economics are very difficult to measure,” admits Keith Bradley, general manager at Fruitways Agri Services. “I tell growers, you’ll have to spend the money now, but you’ll only see the financial benefits later.”

Mulching is one practice which has proved its value, according to Bradley. “Twenty years ago, when people pulled out an orchard, they burnt it, which is the cheapest option. Now, most people are chipping all the product they can, and utilising it in the orchard. It’s an added cost but they’re seeing the benefit of spending the money.”

Health food for trees

“The big reason why I got into mulching was for water retention, when we went through a dry spell,” says Craig Johnson of Nidderdale in the Hemel-en-Aarde Valley.

Mulching not only reduces evaporative water loss, but also improves water infiltration. In addition, mulch is incorporated into the soil over time, increasing the organic-matter content, and consequently the ability of the soil to hold water.

Covering the soil has enabled Johnson to irrigate substantially less, thereby saving both water and electricity. But bringing in material from outside is a big cost factor, so he is exploring cover crops as an alternative to mulch.

“We have a work row that’s not being utilised, so why not grow something there, and just move it half a metre?” says Johnson. “You get to the same end goal of water retention, plus you have the benefits of soil health.”

Whether growers are applying compost or mulch, or growing cover crops, the organic-matter content of the soil will increase, which can lead to some serendipitous effects, according to Pretorius. “Over time, when you put organic material in the tree row, the pH buffering improves.”

At Bokveldskloof, compost and mulch were initially adopted to replace synthetic fertilisers with organic sources of plant nutrients. Compost is placed on top of the soil in the tree row, and then covered with straw or woodchips.

The compost serves as an inoculum that accelerates the biological processes in the soil which make nutrients available to the trees, explains Pohl. The mulch both protects and feeds the microorganisms in the compost.

Pohl believes that trees do best when grown in soil where the microbial community is dominated by fungi. “The microbiology of the soil determines what thrives there. Pioneer plants — what we know as weeds — like a bacterially-dominated soil. Tree growth is promoted by a fungally-dominated soil because that will release the nutrients that trees like in the form that they like it.”

Fungi prefer complex carbohydrates, so Pohl makes sure to use compost that contains sufficient woody material and that has a high ratio of carbon to nitrogen.

Getting into the weeds

Even a short-term view provides compelling reasons for sustainable practices, argues Daan Brink, soil scientist and technical adviser at FruitMax Agri. “We are under enormous pressure to reduce chemical use. We have to look at our alternatives.”

Weedkillers are among the products that are falling out of favour. Brink believes that cover crops will play an increasingly important role in weed control. “Over time, you can reduce the weed seedbank. You’ll still have to spray, but you’ll need to spray so much less often, and you can use less harsh chemicals.”

Besides concerns about the environmental impact of weedkillers, there is also the impression that chemical control of weeds is a losing battle. “All you’re doing with chemicals is selecting for the more problematic weeds,” says Bradley.

Cunningham refers to sustainable weed control as bio-rational. “We’re including normal spray practices, but we’re also using biology and nature.”

In addition to suppressing weeds, cover crops and mulches are potential allies in the fight against pests and diseases. Mulches — whether woodchips or straw — have been shown to suppress woolly apple aphid. This may be thanks to anti-woolly-apple-aphid fungi that grow in carbon-rich mulches.

Biocontrol in orchards is further enhanced by cover crops. Diverse cover crops that contain broad-leaved plants maintain populations of predators which keep plant-eating mites within bounds.

As a soil scientist, Pretorius is particularly interested in the relationship between soil health and apple replant disease. She thinks that, in the past, chemicals were used without understanding their effect on soil ecology. “Soil is not a sterile medium, and the way that we’ve been farming has created an imbalance in soil biology. Now we have challenges with replant disease.”

When it comes to issues like pests and diseases, Pretorius stresses that the industry can’t afford to wait until changes in market requirements have depleted the existing arsenal of control options. “Are we going to hope for solutions — like resistant rootstocks? Or are we going to be proactive and start looking at our soil biology?”

Options for organic matter

Improving soil health basically comes down to adding organic matter as either compost, mulch, or cover crops — or even all of these.

“We put a little compost in our planting holes,” says Pohl. “Thereafter, we spread compost in the tree rows, and cover it with either straw or a woodchip mulch, every year.” Pohl sources compost from a commercial supplier, and woodchips from chipping woody material generated on Bokveldskloof. He produces some straw on the farm, and buys in the rest.

On top of the cost of purchasing straw and mulch, there is the cost of applying it in the orchard. Pohl spreads compost mechanically, but woodchips are distributed manually. Although he hasn’t had trouble obtaining sufficient volumes of either compost or mulch, the reality is that there would be shortages if all growers started using these materials.

“If every hectare in the EGVV region had to be mulched, we’d be trucking in product from as far as the Southern and Eastern Cape,” jokes Bradley.

Whereas Pohl started using compost and mulch to feed his orchards, the motivation for most growers was the urgent need to save water. A layer of either compost or straw on top of the soil will reduce moisture loss, but both disappear rapidly, devoured by soil organisms. Woodchips last longer — and cost more.

“We’ve seen woodchips eaten away within 18 months, when we’ve used compost,” says Cunningham, “We can’t afford to keep bringing in woodchips, but if we stop feeding the system, well then it’s going to crash, after we put all the effort into establishing it.”

Enter cover crops — the grow-your-own mulch solution. Cover crops have the potential to generate enough biomass to serve as mulch, especially in the winter-rainfall areas of the Western Cape. Like any other mulch, cover crops can increase water infiltration, reduce water evaporation, suppress weeds, and build organic matter in the soil.

“What attracts me to living mulches is that their roots are putting organic matter into the soil,” comments Pohl.

Some cover crops go even further, by boosting soil nitrogen. This can reduce fertiliser inputs, but there is also the risk that too much nitrogen at critical periods of fruit development can impact quality.

“My end goal is not to decrease my fertiliser, although less fertiliser will hopefully be an unintended consequence,” says Cunningham. “I’m adding organic matter because I’m seeing the improvement in the condition of the soil, and subsequently in the performance of my trees.”

Cover crops in practice

“Historically, when we planted a new orchard, we tried to establish a permanent cover crop, normally opting for fescue,” recalls Bradley. “So, it was a monoculture. Now we’re talking about planting and replanting multi-species mixtures on a continuous basis.”

In an ideal world, a grower would sow a cover crop once, and from then on, the cover crop would propagate itself. But in the real world, cover crops usually need to be resown regularly. Breaking up the soil surface in the work row to sow cover crops is counterproductive because it accelerates the breakdown of the very organic matter that growers try to boost by planting the cover crop.

Establishing a cover crop involves multiple actions — discing, sowing, covering, and rolling — that compacts the soil. Not to mention the challenges of trying to carry out these actions while simultaneously harvesting fruit, especially when it rains.

To get around these problems, Johnson has teamed up with Stoney Steenkamp of Stoney Agricultural Services, and Carel van Niekerk of Piket Implements to develop a no-till planter for cover-crop seeds.

“The first two years, we grubbed and disced, because of years of compaction,” says Johnson. “This year we did nothing, just used the no-till planter, and the seedlings are coming through.”

Cover-crop seed is available through several companies. The suppliers can recommend winter-growing and summer-growing mixes that are suitable for different soil types. They can also advise on which mixes are best for achieving specific goals such as fixing nitrogen, generating biomass, or countering compaction.

In the winter-rainfall regions, cover crops may need little supplementary irrigation during winter. However, lack of water can lead to disappointing germination and establishment, and poor biomass production, so it’s best to be ready and able to irrigate.

Although many questions remain about cover-crop management, growers are actively experimenting to find solutions for their own orchards. “We’re going to change the species of cover crops that we plant,” asserts Brink, “but we’re not going to change between cover crop and no cover crop.”

With sustainable practices in general, Pohl would like to see more rapid change. “We have to start taking care of our soil, and improving its health. Producers need to make large-scale shifts to sustainability, instead of doing small-scale trials, so that they can see the benefits. Otherwise, they never reach the decision to fully commit to sustainability.”

Image: A diverse cover crop establishing at Bokveldskloof.

Supplied by Matthew Addison | Hortgro.