7 December 2023
Much like the air we breathe and the water we drink, we often take for granted the soil in which our food grows. World Soil Day, celebrated annually on December 5, helps to raise awareness of this life-giving resource, which produces 95% of the world’s food.
With about a third of the world’s soil degraded, according to a UN estimate, this precious resource for growing our food and regulating the climate is at risk. “Soil health matters a great deal,” says Stefan van Zyl from Syngenta Seedcare South Africa. “The reality that the 10-30 cm of topsoil that sustains our ability to grow food could run out in just 60 years is a call to action not a single person or company can afford to ignore.”
World Soil Day 2023 focused on the relationship between soil and water as a source of life. This is of relevance in South Africa, where average annual rainfall of 460mm is about half the global average. But in years of widespread rain showers, damage to cultivated land also plays its role in degrading the soil and hastening erosion.
Healthy soils absorb and purify water for human consumption and regulate the impact of excess rainfall by preventing floods. This ecosystem service will only become more important as climate change causes increasingly erratic rainfall patterns.
Farmers, as the primary caregivers of agricultural soil, must play their part as soil managers in the interest of food security and climate change management.
Holistic approach
The key to protecting and restoring soil health is a holistic approach. “In agriculture, the problem and indeed the solution lie in what we plant and when, and the cultivation practices used,” says Van Zyl. He urges farmers to take particular care of the part of crops most intimately in contact with soils, the roots.
“Far from roots just taking from the soil, the relationship between the two is highly symbiotic. Healthy soils enable and support robust root systems and vice versa.”
Plant roots help bind soil particles together, creating a stable structure, preventing erosion and top-soil loss, improving water infiltration and reducing compaction. Strong root systems also create channels that allow air, water and nutrients to penetrate more deeply. Healthy root systems serve as habitats and sustenance for organisms ranging from earthworms to mycorrhizal fungi, which contributes to ecosystem resilience.
Crop rotation is important
According to Professor Driekie Fourie, nematologist and Syngenta Seedcare team member, nematode pressure increases over time if populations are not managed. Her research also indicates that crop rotation systems used in South Africa are conducive to nematode build-up.
“A holistic management approach is critical, given that plant-parasitic nematodes often open the door to secondary fungal infections and these disease-nematode complexes worsen crop damage,” she says.
Seed treatment is the first line of defence against plant-parasitic nematodes, fungal diseases and insect attacks, but it must be supported by other management practices such as in-furrow applications and weed control.
The shift to conservation agriculture also plays a vital role in finding viable solutions for the soil degradation farmers need to combat. Key to this is the ability to restore carbon to the soil, says Dr Hendrik Smith, agronomist at Asset Research and conservation agriculture organiser for the Maize Trust.
“Letting fields lie fallow without any covering is a self-destroying practice that should be avoided at all costs,” says Smith. Wind erosion damages the topsoil in these fields and is usually followed by water erosion during thunderstorms, which according to meteorologists’ predictions will become heavier as climate change intensifies.
“Soil cover can be provided through crop residue, the plant material remaining after harvesting, including leaves, stalks and roots, but also through cover crops,” says Smith.
Cover crops are often grown during fallow periods between harvesting and planting of commercial crops. While commercial crops have a market value, cover crops are mainly grown for their effect on soil fertility or as livestock fodder. “They improve water penetration and lower the ground temperature. These are two critical factors for utilising our scarce water resources more effectively,” says Smith.
