What Is the Soil Food Web?
Beneath your feet — even beneath a lawn or a vegetable bed — exists one of the most complex and productive ecosystems on the planet. The soil food web is the interconnected community of organisms that live in soil: bacteria, fungi, protozoa, nematodes, arthropods, earthworms, and many more. Together, they drive decomposition, release nutrients, build soil structure, and support plant growth.
Understanding this web transforms how you think about gardening. Rather than feeding your plants directly with synthetic fertilisers, you can feed the soil — and let the soil feed your plants naturally.
The Key Players and Their Roles
Bacteria
Bacteria are the most numerous organisms in soil — a teaspoon of healthy soil can contain hundreds of millions of them. They decompose simple organic compounds, fix atmospheric nitrogen into plant-usable forms, and are a critical food source for higher organisms in the web.
Fungi
Fungi decompose tougher materials like woody stems and lignin. Crucially, mycorrhizal fungi form symbiotic relationships with plant roots, extending far beyond the root zone to bring water and minerals (especially phosphorus) directly to the plant. In return, the plant feeds the fungi sugars produced through photosynthesis.
Protozoa
Protozoa — single-celled organisms like amoeba and ciliates — graze on bacteria. As they eat bacteria and excrete waste, they release nitrogen in a plant-available form. This "microbial loop" is one of the primary mechanisms by which nutrients become accessible to plant roots.
Nematodes
These microscopic worms are extraordinarily diverse. Some eat bacteria, some eat fungi, some eat other nematodes, and some (the plant-parasitic ones) are pests. The beneficial species play an important role in regulating microbial populations and cycling nutrients.
Earthworms
Earthworms are often called "ecosystem engineers." They physically mix organic matter into mineral soil, create channels that improve drainage and aeration, and produce worm casts — concentrated packages of nutrients and beneficial microbes that dramatically improve soil fertility.
Why Decomposition Is Central to Soil Health
The soil food web is ultimately powered by the decomposition of organic matter. Dead plant material, animal remains, and microbial bodies are progressively broken down through the food web — each organism consuming another and releasing nutrients in the process. This is why adding organic matter to your soil (as compost, mulch, or plant cuttings) is so powerful: you are directly fuelling the entire ecosystem.
Signs of a Healthy Soil Food Web
- Soil is dark and crumbly, not hard or compacted
- Earthworms are visible when you dig
- A pleasant earthy smell (caused by a compound called geosmin, produced by bacteria)
- Water soaks in readily rather than pooling on the surface
- Plants grow vigorously with minimal additional feeding
- Little need for pest control — healthy soil food webs suppress many pests naturally
How to Support Your Soil Food Web
- Add organic matter regularly. Compost, leaf mulch, green manures, and wood chip mulch all feed the web. Apply as a top dressing and let organisms draw it down — don't bury it by deep digging.
- Minimise tillage. Digging and rotavating destroys fungal networks, disrupts structure, and brings weed seeds to the surface. No-dig or minimal-dig approaches preserve the food web.
- Avoid synthetic fertilisers and pesticides. High-nitrogen synthetic fertilisers can suppress mycorrhizal fungi (plants no longer need the fungi if nutrients are delivered directly). Pesticides can devastate invertebrate populations.
- Keep soil covered. Bare soil loses moisture, temperature-regulates poorly, and suppresses microbial life. Use mulch or cover crops to keep the surface protected.
- Grow diverse plants. Different plant roots support different microbial communities. Diversity above ground creates diversity below.
The Bottom Line
Healthy soil is not just dirt — it's a living system. Every handful of rich garden soil contains more organisms than there are people on Earth. By understanding and supporting the soil food web, you move from fighting nature to working with it — and your garden will be healthier, more resilient, and far less work as a result.