Over the past 60 years, scientists have noticed alarming changes in the nutrient values of the food we eat. A popular article, Mineral Depletion of Foods Available to Us as a Nation (1940 – 2002) – a Review of the 6th Edition of McCance and Widdowson, discusses these changes in detail. It shows that the nutrient levels in food have decreased between 10 and 100%.

Table 1 illustrates the significant decline in essential minerals in roast chicken between 1940 and 2002. Closer inspection reveals how levels of potassium, phosphorus, calcium, and iron declined significantly between 1940 and 1991. Between 1991 and 2002 trace elements either increased or remained stable.

Table 1: Roast chicken: Trace elements in mg/100g between 1940 and 2002. (Source: McCance and Widdowson)

 1940 (mg/100g)1991 (mg/100g)2002 (mg/100g)1940 – 1991 % change1991 – 2002 % change1940 – 2002 % change
Copper 0,120,08-48-330
Zinc 1,52,7 80 
Water61,1 65,3  7

Maintaining healthy soil is a sure-fire way to increase the nutrient density of food. Soil without living organisms serves no purpose for growers, which is why it is important to balance its chemistry, physical structure and biology. Unfortunately, some land-use operations, such as industrial agricultural practices, mining, and construction and development, tend to harm soil quality.

Common causes of soil damage include long-term chronic toxicity, pollution due to irresponsible or unbalanced application of herbicides, irrigation and drainage, grazing, tillage, fertilisers or contaminants. Pesticides and insecticides that damage macrofauna (animals that are 1cm or longer in length, but smaller than an earthworm) in the soil can also harm its health and calls into question whether it is possible to revive dead or damaged soil.

Diagnosing soil problems

Dawie van Rensburg of SWP AGRI believes that soil can be revived by following a few crucial steps. He says the process begins with evaluating photosynthesis, making a checklist to measure the soil’s ‘vital signs’, diagnosing the problem, determining which treatment is required and taking responsibility for the environment.

“One can compare the process of restoring soil to a person who visits a doctor to treat an ailment,” he says. “The doctor follows all the necessary steps, such as conducting a visual assessment and monitoring the patient’s vital signs and general condition, to establish whether more information, such as blood tests, will be required for the correct diagnosis. The information is carefully recorded so that the patient’s treatment intervention can be monitored with the aim of curing the ailment or condition.”

Soil is a crucial component of farming and farm health. How we work with it today, will determine the sustainability of providing nutrient-dense food for future generations.

Although soil cannot talk, decreased crop yields and lower nutrient density in fresh food can point to problems. According to Dawie, soil biology, or the lack thereof, is one of the most important assessment indicators of soil health. He refers to four important vital signs that help assess soil condition, namely biology, chemistry, physics, and carbon content.

Ticking all the boxes

Soil science and technology is the study of measuring soil health to help producers conduct a sound analysis of the soil. It usually requires the assistance of soil health experts who can establish, monitor, and manage soil health and quality.

Soil health management plans that can help present an accurate picture of the balance between soil’s chemistry, biology, physics, and carbon, include the following:

  • The application of devices to measure a range of soil properties.
  • Conceptual systems that explain soil properties, processes and management.
  • Management systems that use the results of soil health monitoring to determine soil inputs and management.

“With the help of a diagnosis,” says Dawie, “one can treat and monitor the soil quality’s improvement and ultimately restore it.”

It is impossible to perform a scientific assessment of soil problems without the correct instruments because they reduce the likelihood of implementing unsuitable interventions that will result in less-than-average or damaging results.

Enhancing soil restoration

Dr Hendrik Smith, conservation agriculture facilitator at Grain SA, and Willie Pretorius of Soil Health Solutions, agree that many producers worldwide have made significant improvements to soil health in a short period.

These producers have applied a few fundamental principles in their farming practices, including:

Minimising soil disturbance

The use of no-till planters without any other tillage practice is ideal for reducing mechanical soil disturbance and restoring soil. Physical soil disturbance, such as tillage with a disc or chisel plough, results in bare or compacted soil, which is destructive and disruptive to soil microbes. It creates a hostile environment in which these microbes must live and work.

Chemical and biological disturbance of soil through the misuse of inputs such as fertilisers and pesticides, disrupts the symbiotic relationship between microorganisms and crop roots. If you were to strategically reduce chemical inputs, you can take advantage of the soil ecosystem services that will allow plants to access essential nutrients freely.

Diversifying with crops and animals

Plants release the sugars made through photosynthesis into the soil as liquid carbon via their roots and trade them to soil microbes for nutrients to support plant growth.

This soil ecosystem service is a vital element of healthy soil and can be restored or enhanced through the inclusion of as many different plants and animals as is practical. For example, livestock that utilise cover crop mixtures contribute to this diversity. Livestock in intensive grazing systems can stimulate root development and recycle 80% of nutrients in the form of dung by utilising 30 to 50% of available material. Biodiversity directly leads to a diverse array of soil microbes from a range of functional groups, which again improves the soil’s ability to support nutrient-dense, high-vitality crops, pastures, fruit and vegetables.

Biodiversity is any agricultural system’s key to success. Lack of biodiversity severely limits the potential of any crop system, which leads to an increase in disease and pest problems. A diverse and fully functioning soil food web or soil biology supports nutrient, energy, and water cycling that allows soil to express its full potential.

Growing living roots all year round

Many sources of nutrients in the soil feed it, but there is nothing better than the liquid carbon exuded by living roots. It is a product of photosynthesis and depends on the crop system’s design and photosynthetic capacity. Maximum capacity is a function of crop density and diversity, which means the greater the variety of plants and/or leaves that cover the soil to absorb solar energy, the higher the capacity.

Soil organisms feed on liquid carbon from living plant roots first. Next, they feed on dead plant roots, followed by aboveground crop residues, such as straw, chaff, husks, stalks, flowers, and leaves. Lastly, they feed on other organisms that are lower in the soil food web.

Soil restoration and healthy soil depend on how well the soil food web functions. The provision of abundant and diverse food that is easily accessible, such as liquid carbon exudate from plant roots, helps microbial communities in soil to colonise, diversify and recycle nutrients for plants to grow. It also builds soil aggregates or structure, which is vital for improving the soil sponge for water storage and infiltration.

Therefore, the soil ecosystem’s functioning is determined by the presence, diversity, and photosynthetic rate of actively growing green plants and roots. Cover crop mixtures produce root exudates with varying composition and effects, establish root pathways and have different zones of nutrient uptake, because they differ in amount, depth, and patterns of root branching.

Permanent organic soil cover

Soil should always be covered by growing plants and/or their residues, and it should rarely be visible from above. Mulch keeps the soil cool and moist, and provides a favourable habitat for many organisms that begin residue decomposition by shredding residues into smaller pieces. A good soil cover protects it against water and wind erosion, stops water from running off, and allows it to infiltrate into the soil.

Soil is a crucial component for farming and farm health. How we work with it today will determine the sustainability of providing nutrient-dense food for future generations. – Carin Venter, FarmBiz

For more information, contact
Dawie van Rensburg on 082 609 7770 or dawie@swpagri.co.za,
Willie Pretorius on 083 458 9854 or willie@soilhealthsolutions.com, and
Dr Hendrik Smith on 082 331 0456 or hendrik.smith@grainsa.co.za.