Life in Earth’s oceans depends on plankton. Teeny weeny organisms. Some are barely visible to the human eye, many are too small to see. But without them, we’d have no fish, no crabs, no sharks, no whales. Plankton are the foundation of the ocean food web.

Life on land follows the same pattern. It’s the teeny weeny soil organisms, trillions of bacteria, fungi, actinomycetes, protozoa & many more, which are fundamental to life above ground. In Master Composter Steve Watts’ previous soil stories, he explored why soil matters and some of the signs of healthy soil. He looked at how soil supports plants, stores water, stores air and holds nutrients – the foundation for life in our gardens. But what actually makes healthy soil?

Well, to a very large degree, it’s soil biology – trillions upon trillions of soil organisms, 99.9% of which we will never see. Together with plant roots, this underground community is the Soil Food Web. The diagram below shows a simplified version of the soil food web, the interacting community of bacteria, fungi, actinomycetes, protozoa, nematodes, mites, springtails, beetles, earthworms and a multitude of other organisms.

It All Starts With Plants

Plants capture energy from the Sun, using photosynthesis to create sugary carbohydrates. Some of these carbs are transferred below ground to the root system. Why? Well, plants need more than just carbohydrates. They also require nutrients like nitrogen, potassium, phosphorus, calcium, magnesium, zinc and quite a few more. And this is where the Soil Food Web comes in. It’s the soil ecosystem which enables the plant to access these nutrients.

Nature’s Recyclers

Nutrients are tied up in living plants and animals. As plants/animals die, these nutrients can be recycled and reused. This what the soil food web does, it releases tied-up nutrients, ultimately converting them into a form which plants can use. Bacteria are the first to consume new organic material. Fungi tend to consume tougher cellulose & lignin material. Protozoa and nematodes consume other microbes. Every time an organism feeds, waste nutrients are excreted in a form that’s more available to plants. And a plants’ root zone is a hotspot for this activity.

The Magic

A plant requires differing levels of nutrient as it matures – nitrogen is great for growing leaves and roots, whereas more phosphorus is needed for flowering, and higher potassium & calcium levels when producing fruits. So the plant conducts a conjuring trick. It feeds the soil food web with sugary carbs, but not just any old carbs. It’s smart enough to understand its own nutrient requirements. So, the plant exudes a specific flavour of carb, a carb which will enable certain microorganisms to flourish in its root zone, microorganisms which provide the nutrients it requires. Magic!

Meanwhile, mycorrhizal fungi form mutually beneficial relationships with plant roots. Fungal hyphae extend the plants’ root system, helping the plant to access additional nutrients and water. More magic. Science continue to discover just how extensive and important these underground fungal networks can be. In healthy soils, they help connect plants, improve nutrient uptake and contribute to the overall resilience of the ecosystem.

Diversity Matters

A healthy soil food web depends on diversity. Different organisms perform different roles, and the interactions between them help keep the whole system functioning.

When soils contain a wide variety of bacteria, fungi, protozoa, nematodes, arthropods and larger soil organisms, nutrients cycle more efficiently, soil structure is built and pathogens kept at bay. This activity creates many of the characteristics we associate with healthy soil. Water infiltrates more easily, moisture is retained more effectively during dry periods, nutrients are recycled naturally and plant roots can grow more successfully.

Healthy soils can also store significant amounts of carbon, helping support climate resilience. In many ways, the health of a garden aligns with the health of its soil food web.

Supporting the Soil Food Web

The encouraging news is that gardeners can support this hidden community through relatively simple actions.

• Provide a feedstock. Add compost, or just leave dead plant material on the soil surface to break down naturally.
• Minimise soil disturbance. Undisturbed soil has higher levels of microbes and therefore more nutrient recycling.
• Keep living roots in the soil – it’s living plants that sustain the soil food web by providing it with energy.
• As far as possible, avoid pesticides and manmade fertilisers. These can kill beneficial microbes / disrupt soil chemistry.

The next time you are gardening, take a moment to think about what is happening below the surface. Each handful of healthy soil contains an astonishing diversity of life, quietly working away day and night. We often celebrate the birds, bees and butterflies that visit our gardens. The soil food web reminds us that some of the most important wildlife is hidden beneath our feet