What role does the soil food web play in nutrient cycling?

The soil food web drives nutrient cycling by converting organic matter and mineral compounds into plant-available forms through a layered chain of feeding interactions. Bacteria and fungi break down raw organic material first; predators such as protozoa and nematodes then consume those microbes, releasing nutrients in soluble forms that plant roots can directly absorb.

How does the soil food web transfer nutrients to plants?

The soil food web transfers nutrients through the microbial loop. Bacteria and fungi decompose organic matter and lock nutrients inside their cells. When predatory organisms eat those microbes, they excrete excess nutrients as ammonium, phosphate, and other soluble compounds directly in the root zone, where plants absorb them almost immediately.

This release is far more targeted than simple chemical dissolution. Because predation happens in the rhizosphere, nutrients appear precisely where root hairs are active, reducing leaching losses. Plants actively stimulate this process by releasing root exudates — sugars and organic acids that feed specific microbial communities and effectively drive their own nutrient supply.

What organisms make up the soil food web?

The soil food web spans five functional groups: primary decomposers (bacteria and fungi), microbial grazers (protozoa and nematodes), secondary predators (predatory nematodes, mites, and spiders), ecosystem engineers (earthworms and beetles), and plant-symbiotic specialists (mycorrhizal fungi and nitrogen-fixing bacteria).

Bacteria and fungi: the primary decomposers

Bacteria dominate moist, nutrient-rich microsites and rapidly decompose simple sugars and proteins. Fungi excel at breaking down lignin and cellulose. Mycorrhizal fungi extend hyphae far beyond the root zone, multiplying the plant’s foraging surface and delivering phosphorus and micronutrients in exchange for carbon.

Fauna: the predators that release nutrients

Protozoa are the primary grazers of soil bacteria, releasing nitrogen as ammonium in the process. Nematodes graze on bacteria and fungi, while predatory nematodes regulate populations below them. Earthworms physically mix organic matter, fragment residues, and create stable aggregates that protect microbial habitats.

What happens to nitrogen and phosphorus in the soil food web?

Both nutrients follow the same fundamental pathway: immobilisation into microbial biomass followed by release through predation. Bacteria consume organic nitrogen, retain what they need, and excrete the surplus as ammonium. Phosphorus is released similarly, with mycorrhizal fungi producing phosphatase enzymes that cleave phosphate from organic compounds and access pores too small for roots to enter. Where mycorrhizal populations are suppressed, phosphorus uptake drops sharply even in soils with adequate total phosphorus content.

How does organic matter quality affect soil food web activity?

Organic matter quality determines which organisms thrive and how quickly nutrients cycle. Low carbon-to-nitrogen materials such as legume residues fuel rapid bacterial growth and fast nutrient release. High carbon-to-nitrogen materials such as straw favour fungal communities and slower release. Stable humic compounds provide long-term energy and habitat for soil microorganisms. A 2025 PMC peer-reviewed review confirmed that humic acids improve cation exchange capacity, water retention, and aggregate formation — all conditions that sustain diverse microbial communities. Building a resilient food web requires both labile organic matter and stable humic compounds.

What disrupts the soil food web?

Compaction, excessive tillage, synthetic pesticides, and organic matter depletion are the primary disruptors. Compaction reduces pore space and eliminates microhabitats. Intensive tillage breaks fungal networks that take months to re-establish. Synthetic fungicides and fumigants directly reduce microbial populations, suppressing nutrient cycling for a full season or longer. According to the European Environment Agency’s 2025 briefing, over 60% of EU soils show signs of critical functional loss — representing soils where the food web can no longer support efficient nutrient cycling without external inputs.

How can growers support a healthy soil food web?

Consistent organic matter supply, minimal soil disturbance, living root cover, and biology-friendly inputs are the foundations. The most impactful practices include:

• Reducing tillage intensity to preserve fungal networks and soil aggregate structure
• Incorporating cover crops to maintain living roots and a continuous supply of rhizosphere exudates
• Adding diverse organic inputs, including compost, crop residues, and soil conditioners, to maintain both labile and stable carbon fractions
• Avoiding broad-spectrum soil pesticides where alternative options are available
• Rotating crops to diversify root exudates and residue types, supporting a broader microbial community

Soil conditioners rich in humic compounds support food web recovery in degraded soils. Products such as NeoTerra™ soil conditioners, produced from responsibly sourced Nordic peat, have a prebiotic effect that stimulates microbial establishment and activity while improving soil structure and water retention. The EU Soil Monitoring Law, which entered into force in December 2025, reinforces what soil science has long demonstrated: a biologically active soil is the foundation of sustainable, profitable farming — and supporting the soil food web is the most cost-effective way to reduce fertiliser dependence and build long-term productivity.