Laying the groundwork for productive orchards. By Grethe Bestbier.
Maintaining soil health is important for many reasons. Soil sustains all forms of terrestrial life and underpins successful crop production. Soil also stores carbon, thereby slowing climate change. Entomologist Matthew Addison, crop protection programme manager at Hortgro Science, explains the benefits of preserving soil health.
Soil is a living system. Microbial communities found in soil maintain soil health, which in turn sustains the productive functioning of land-based ecosystems. As Addison puts it, you can grow a plant in sterile soil, but it’s not going to be a happy plant, and it certainly won’t give you a healthy crop.
“We call it ecosystems services,” says Addison, referring to the many and varied benefits provided by a healthy soil ecosystem. “Healthy soil, for example, retains water. The more good stuff found in the soil, like organic carbon, acids, and organic material, the more it acts as a sponge, slurping up water and holding it. Roots are happy and consequently activity in the soil is increased.”
Diversity is key
Soil health management requires an integrative approach which recognises the physical, biological, and chemical properties of soils for improved ecosystem productivity and quality. It is the biological component which especially interests Addison.
According to Addison, biodiversity is the foundation of soil health. Soil biodiversity is a measure of the number and variety of organisms occurring in and on the soil. These organisms are all part of a complex network of relationships based on feeding patterns and energy flows.
“The more diversity in the soil, the better,” says Addison. “One way of obtaining this biodiversity is through diversifying the plants in a system over time. By doing this, you accumulate carbon, increase nutrient availability, and improve soil health within the agro-ecosystem.”
Plant diversity can be improved by crop rotation or crop cycling, which refers to planting different crops sequentially on the same plot of land. Plant diversity can also be promoted by the establishment of diverse cover crops within and on the margins of orchards. Both methods will improve soil health and combat pests and diseases.
Increased diversity in the soil is thought to reduce the risk of disease due to increased ecosystem stability. The diversity-stability hypothesis is the view that the more diverse an ecosystem, the more likely that certain organisms within that system will survive during environmental changes. The result is a resilient soil ecosystem that recovers quickly after disturbance.
More frequent outbreaks of pests and diseases are warning signs of an unbalanced system, suggesting that the soil is not as healthy as it could be. Apple replant disease, woolly apple aphid, and plant-eating mites are some of the potential indicators of declining soil health.
Savvy soil-management practices
Diversity is not the only benefit of good soil-management practices. Cover crops are to soils what hats are to foreheads: they protect the soil from sunburn and erosion, all while improving soil health. Cover crops have been shown to increase crop yields, and to create a habitat for soil microbes. A mix of cover crops that includes a grass, a brassica, a legume, and a broad-leafed plant, seems to work the best.
In many places, soil health has been critically reduced by decades of over-cultivation and poor management practices, especially in row crops. The accepted way of doing things was built upon a tradition of planting the same crops year after year, which creates a slow decline in soil health and quality.
Agricultural practices, such as tilling, that disturb the soil disrupt microbial communities, and expose soil carbon to oxygen. This causes the loss of carbon to the atmosphere and the decline of soil carbon levels. In addition, preparing, amending, and correcting a virgin soil for cultivation is often necessary for crop production, but can impact soil health and carbon levels.
Soil organic matter sequesters carbon, and naturally removes carbon dioxide from the atmosphere. Maintaining soil organic matter is therefore critical to tackling climate change.
“When asked whether we should be sequestering carbon into our soils, I believe that it’s the way to go,” says Addison. “Incidentally, we can get all lyrical about cutting out diesel consumption, and other ways of decreasing carbon emissions, but the only way to store such massive amounts of carbon is in the soil.”
The way forward is regenerative agriculture
Declining soil carbon levels, and associated losses in soil health and productivity are critical issues globally. The proposed solution — regenerative agriculture — has become a buzzword in recent decades.
“Regenerative agriculture tries to help damaged soil by employing various regenerative practices, such as planting cover crops, mulching, integrating livestock, and ploughing as little as possible,” explains Addison.
Addison believes that the profit-at-any-expense philosophy is on its way out. Drastic measures to preserve soil health are unavoidable if growers wish to ensure future success. The golden rule, says Addison, is to not disturb your soils unnecessarily.
“After you’ve established an orchard, it’s important to not again disrupt the soil after planting. Some forward-thinking farmers are relying on minimum tillage when planting cover crops. They don’t plough the soil, but rather drill into the soil, cut a small trench to open it up, drop the seeds into the trench and close it up neatly.”
More than ever before, producers need to understand the intricate relationship between soil-management practices, soil carbon levels, and soil health. Industry and researchers will have to work together to test and implement changes that can restore soil health.
“Especially in the last five years, we’ve been developing, researching, and learning more as we go along,” says Addison. “It’s not a system that can be fixed in ten minutes. We need to find out what we’re doing that’s right, and what’s wrong, and work out the complexity behind the linkages that exist.”