Soil health remains one of the most widely used yet least precisely defined concepts in modern agriculture, according to associate professor Gerhard du Preez, a researcher and senior lecturer in the Unit for Environmental Sciences and Management in the agriculture division at North-West University. With expertise in nematology and soil health, he says the meaning of the term continues to vary depending on context, management system and how it is interpreted at farm level.
Speaking to Farmer’s Weekly, Du Preez explains that the term is inherently difficult to pin down in strict scientific language, despite its increasing importance in discussions around sustainability, productivity, and regenerative agriculture.
“The short and the long is that soil health is an abstract term. If you ask a farmer what he thinks soil health is, and you ask the next farmer, they will probably give you different ideas and different definitions,” he says.
While researchers continue working to develop measurable indicators, he argues that the practical value of soil health lies less in definition and more in function within production systems.
“In terms of it actually being tangible and measurable, I know we still have some way to go. But when we think about what health means, we have to think about it from a functional point of view. In other words, it needs to have a benefit to farmers,” says Du Preez.
Soil health as a functional outcome
From a farming perspective, soil health is best understood through the services soil provides to crops and production systems. These include nutrient availability, improved water retention and stronger resilience under environmental stress.
“If we work towards promoting soil health, what we should expect is a soil that can deliver services to farmers. That can include increased soil fertility, so more nutrients are available for plants, which ultimately requires less fertiliser input,” he says.
Carbon is central to this functioning. Increasing soil carbon levels improves structure, water-holding capacity and overall system stability.
“We can think about healthy soil as soil that is storing more carbon. With more carbon, there is potential to increase water-holding capacity. It also reduces carbon in the atmosphere,” he says.
The link between soil and plant performance
Du Preez says that soil health cannot be separated from plant health, as the two operate as a single integrated system.
“If you have healthy soil that supports a healthy plant, then the plant has an increased ability to protect itself against pests and diseases. Plant health is therefore interlinked with soil health. We are looking at a healthy environment, not just the soil itself,” he says.
Biology as the driver of soil function
At the core of soil performance is its biological community. Micro-organisms regulate essential processes such as nutrient cycling, decomposition, and organic matter turnover.
“It is actually the biology in the soil that performs all these processes and ultimately deliver those services,” says Du Preez.
Context determines outcomes
Du Preez says one of the most important realities of soil management is that outcomes are highly context specific. Soil type and climate and production systems all influence results, making universal recommendations unreliable.
“What you do in one area to promote soil health might not work in the same way in another area. Soils are inherently different, and climatic conditions also influence crops and soil biology,” he says.
Because of this variability, he warns against simplified prescriptions.
“There is not necessarily just one practice or system that can be implemented across all regions that will guarantee increased soil health.”
Managing soil health through adaptation and experimentation
Rather than relying on fixed formulas, Du Preez says farmers should adopt an adaptive approach grounded in observation and on-farm trials.
“Every farmer should be doing on-farm experimentation to test crops, cultivars, products and practices, and then measure soil health to see the effect,” he says.
He adds that while regenerative and conservation agriculture principles provide useful direction, they must be interpreted and adjusted for local conditions.
The hidden biological system beneath the soil
Beneath the surface lies a highly complex and interconnected biological system that drives most soil functions. Du Preez describes diversity as the foundation of this system.
“A key factor is diversity. In agricultural systems, a single species is rarely going to deliver all the benefits we need,” he says.
Soil health depends on the interaction of multiple functional groups rather than isolated organisms.
“The key is to promote general diversity across different feeding groups.”
How the soil food web functions
The soil ecosystem begins with plant roots, which release exudates that act as a food source for micro-organisms.
“These exudates become available to microbes such as bacteria and fungi,” says Du Preez.
These microbes form the base of the soil food web and support higher organisms such as nematodes and arthropods.
“You then have organisms feeding on bacteria and fungi, such as nematodes, and then others feeding on those again. So the cycle continues,” he says.
Nutrient cycling and natural regulation processes
Through these biological interactions, nutrients are continuously recycled into plant-available forms.
“When a nematode feeds on a bacterium, not all energy is used. What remains is released back into the environment in a form plants can uptake. That is nutrient cycling,” says Du Preez.
The same system also contributes to natural pest regulation through predation within the soil food web.
“A predatory nematode can feed on plant-parasitic nematodes, so pest regulation happens in the soil as well,” he says.
However, he cautions that these functions rely on maintaining system complexity and balance.“ Only having one or two species is not sufficient for a fully functioning biological community.”
Diversity as a foundation for resilience
Beyond supporting soil processes, diversity also improves system stability under stress.
“With greater diversity, we have higher resilience. If there is drought, flooding or disturbance, some species may die out, but others will continue functioning,” he says.
This functional redundancy helps maintain productivity even under variable conditions.
Declining soil health
Du Preez says that in many agricultural systems, soil health has already been degraded, meaning farmers are more likely to observe changes during recovery than during early-stage decline.
“In most agricultural systems, soil health has already declined. So you are more likely to see improvement when management starts focusing on it,” he says.
One of the most reliable indicators of decline is a reduction in soil carbon levels.
“The more you work the soil, the more carbon is exposed to oxygen and lost through microbial activity,” he says.
He adds that carbon is central to soil functioning.
“Reduction in carbon stocks is a clear indication of reduced soil health. Carbon is central to all living processes in soil,” says Du Preez.
Other indicators include rising pest and disease pressure, as well as increasing reliance on external inputs.
“If soil health is low, fertility is low, and farmers may need to add more fertiliser,” he says.
Influence on soil systems
Du Preez says that agriculture must be understood as a managed system, where human interventions directly reshape soil biology and function.
“Agriculture systems are anthropogenic systems. They are managed by humans, not natural systems,” he says.
Tillage and chemical impacts
Mechanical tillage disrupts biological networks within the soil, particularly affecting larger organisms such as earthworms, and breaking fungal networks responsible for nutrient transport.
“Every time we till the soil, we are breaking up biological networks,” says Du Preez.
He adds that repeated disturbance can reduce both organism abundance and functional capacity. Chemical inputs can also have unintended consequences, particularly when beneficial organisms are more sensitive than target pests.
“You might be targeting a plant-parasitic nematode, but your beneficial organisms will likely die out first because they are generally more sensitive,” he says.
For this reason, he recommends minimising unnecessary disturbance to allow biological communities to recover.
Restoring degraded soils over time
Soil restoration is possible, but timelines depend heavily on environmental and management conditions.
“We have seen restoration of soils over fairly short periods. Within two or three years, you can start seeing small changes,” says Du Preez.
However, factors such as soil type, rainfall, and management capacity strongly influence outcomes.
He adds that while early improvements can emerge relatively quickly under improved practices such as reduced tillage and increased diversity, more substantial recovery typically takes longer.
“Realising the bigger benefits that we are hoping for would generally take between five and 10 years,” he says.
Misconceptions in soil management
One common misconception is the underestimation of native soil biology and its role in system recovery.
“Farmers do not always realise the importance of native biology that naturally occurs in their environment,” says Du Preez.
He also cautions against over-reliance on biological input products without sufficient scientific validation.
“There are many products being sold that do not have strong results backing them,” he says.
He advises farmers to rely on independent trial data and to test products on a small scale before full implementation.
Monitoring soil health in practice
While laboratory testing provides useful baseline information such as organic matter content, Du Preez emphasises that field observation remains essential.
“In a healthy system, you should see greater biodiversity, especially insects,” he says.
Earthworm presence is another practical indicator of improving soil conditions.
“If you dig into the soil, you should start noticing more earthworms,” he says.
Ultimately, soil health monitoring requires consistent engagement with the land.
“You need to walk your fields and observe both crops and soil,” says Du Preez.
