The Soil Food Web
How billions of organisms in your soil work together to feed plants, cycle nutrients, and build structure. The complete guide to soil biology for organic farmers.
The soil food web is the community of organisms living in soil — from bacteria too small to see, to earthworms you can hold. Every organism feeds another, and through this web, nutrients are cycled, structure is built, and plants are fed.
Key insight: Plants do not directly absorb most nutrients. They trade with microbes — giving sugars, receiving minerals. Destroying microbes with chemicals breaks this supply chain permanently.
What Lives in a Teaspoon of Healthy Soil
| Organism | Count in Healthy Soil | Destroyed Soil |
|---|---|---|
| Bacteria | 100 million to 1 billion | 1 to 10 million |
| Fungal hyphae length | Several kilometres | A few metres |
| Protozoa | 10,000 to 100,000 | Less than 1,000 |
| Nematodes | 100 to 1,000 | Less than 50 |
| Earthworms per sq metre | 200 to 500 | 5 to 15 |
A teaspoon of healthy soil contains more living organisms than there are people on Earth.
How the Food Web Works
Sunlight enables plants to photosynthesize. Plant roots exude sugars and amino acids into the surrounding soil, feeding bacteria and fungi. These bacteria and fungi are eaten by protozoa and nematodes, which release plant-available nitrogen (ammonium) as a waste product, right at the root zone.
Protozoa and nematodes are in turn eaten by larger arthropods. When all these organisms die, they are decomposed by bacteria and fungi again, forming humus. This humus holds nutrients tightly via cation exchange capacity and releases them slowly.
This is why organic systems work — the food web is the fertilizer system. It runs itself, for free, forever, as long as you feed it organic matter and stop poisoning it.
Mycorrhizal Fungi — The Underground Network
Mycorrhizal fungi are arguably the most important organisms in organic soil. They form a symbiotic relationship with 80% of all plant species.
The exchange:
- The plant gives fungi 20 to 40% of its photosynthetically fixed carbon
- The fungi give the plant water, phosphorus, zinc, copper, and other micronutrients
Mycorrhizal hyphae extend the effective root surface area by 100 to 1,000 times. A plant with a functioning mycorrhizal network can access nutrients that its physical roots could never reach.
What Kills Mycorrhizal Fungi
- Phosphate fertilizers — the plant stops trading when phosphorus is artificially abundant
- Fungicides — directly toxic to fungi
- Repeated deep tillage — shreds hyphal networks
- Soil fumigation
- Leaving soil bare for extended periods
In organic systems, never applying synthetic phosphate means the mycorrhizal network thrives, and the plant gets phosphorus for free, indefinitely.
Nitrogen-Fixing Bacteria
Free nitrogen makes up 78% of the air. Most plants cannot use it. These bacteria can:
| Bacteria | Association | N Fixed per Hectare per Year |
|---|---|---|
| Rhizobium | Legume root nodules | 50 to 300 kg |
| Azotobacter | Free-living in soil | 20 to 30 kg |
| Azospirillum | Associated with grasses | 10 to 40 kg |
| Anabaena in Azolla | Paddy fields | 20 to 40 kg |
With good legume rotation and Rhizobium inoculation, an organic farmer can get 50 to 300 kg of free nitrogen per hectare every year — the equivalent of 100 to 600 kg of urea, at zero cost.
Earthworms — Nature's Tiller
Earthworm castings are the highest-quality soil amendment produced naturally:
| Property | Worm Castings vs Surrounding Soil |
|---|---|
| Available nitrogen | 5 times higher |
| Available phosphorus | 7 times higher |
| Available potassium | 11 times higher |
| pH | Near-neutral regardless |
| Microbial activity | Extremely high |
A healthy population of 200 to 500 earthworms per square metre physically tills 50 tonnes of soil per hectare per year. They create channels for air and water, buffer pH, and suppress pathogens through gut enzymes.
How to Restore Earthworms
- Stop or reduce tillage to surface only
- Add compost or mulch as their food source
- Stop all synthetic pesticides, especially nematicides
- Maintain consistent soil moisture
- Keep soil covered at all times
Earthworm populations can recover from near-zero to healthy in 2 to 3 years with consistent organic management.
Building Your Soil Food Web
This season — immediate actions:
- Apply Jeevamrutham every 15 to 21 days, delivering billions of microbes per application
- Apply compost at 2 to 5 tonnes per hectare as microbial food
- Mulch the soil surface to retain moisture and feed surface organisms
Year 1 to 2 — medium-term:
- Inoculate seeds with mycorrhizal fungi, Rhizobium, Azotobacter, and PSB
- Plant legumes in rotation
- Stop all synthetic inputs
- Reduce tillage depth gradually
Year 3 onwards — long-term:
- Establish permanent soil cover with cover crops or mulch
- Introduce vermicomposting to produce high-quality inoculant
- Build organic carbon from 0.5% toward 1.5%
The soil food web, once established, maintains itself. Your job is simply to stop disturbing it and keep feeding it organic matter.