What Is the Soil Food Web?

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What is the soil food web? It is the set of living organisms in soil that feed on plants, on decaying material, and on each other. The National Park Service describes it through a few main groups: arthropods, nematodes, protozoa, and the bacteria and fungi that break down organic matter. Energy and carbon move through this web in steps, and each step changes what plants can later use. This explainer covers the groups, how energy moves, how nutrients reach plants, and where the sources stop.

Quick answer

• The soil food web is the network of soil organisms that feed on one another, and the National Park Service ties it to a healthy soil system.
• Bacteria and fungi break down organic matter, and the Park Service says organic matter forms from rotted and decomposed vegetation.
• Carbon and energy enter the web through plant, bacterial, and fungal feeding, then pass up through predators, according to a PMC review of nematodes.
• Each step in the web loses some carbon and energy, so the web’s structure depends on how much energy enters it.

Who lives in the web

The National Park Service lists several groups. Arthropods are invertebrates with segmented bodies and jointed legs. The Park Service says that arthropods perform many different functions in the soil community. Some arthropods eat plants, while others feed strictly on fungus. Others aerate the soil and shred organic matter into small pieces, which helps other soil organisms in the decomposition process.

Nematodes are the second main group. The Park Service describes them as tiny roundworms that are common in soils everywhere. Some graze on bacteria and fungi, and others feed on decaying plant material. Protozoa are tiny single-celled animals that mainly feed on bacteria.

Larger animals also belong to the web. The Park Service notes that small mammals consume and help control soil arthropod populations, and that soil arthropods are in turn consumed by burrowing mammals, birds, and lizards. Arthropods sit in both roles in this list. Some eat plants or fungus, and others are consumed by burrowing mammals, birds, and lizards.

How energy moves through the web

The PMC review describes the energy source for the web. The organisms of the soil food web derive carbon and energy through plant-, bacterial-, or fungal-feeding, and through successive levels of parasitism or predation. In other words, the first feeders depend on plants, dead material, or microbes, and the energy then moves up to the organisms that eat them.

That movement is not lossless. The review states that consequently, carbon and energy dissipate during the course of successive exchanges. Their availability affects the structure, dynamics and activities of the food web. The review ties a long web to a high rate of rhizodeposition or detrital subsidy, which are carbon inputs to the soil.

The review also links web length to the supply of resources. Food webs driven by sparse resources, as in desert systems, or by periodic pulses of resources, as in some agricultural systems, are likely to be short and dominated by opportunists at the entry level. The review describes webs of that kind as dominated by opportunists at the entry level.

Disturbance changes the balance further. The review says disturbed soil food webs tend to be bottom heavy and recalcitrant to restoration. The reasons it gives include the slow growth of upper predator populations, physical and chemical constraints of the soil matrix, and biological imbalances. Recovery can be slow because the predators that keep the web balanced grow slowly.

How the web feeds plants

The Park Service explains the plant link through decomposition. Organic matter forms from rotted and decomposed vegetation that soil organisms break down. The Park Service states that increased organic matter concentration and decomposition boost nitrogen and phosphorus levels.

Soil arthropods play a direct role in that conversion. Through consumption, digestion, and excretion of soil organic matter, they help improve soil structure and change nutrients into forms available to plants. The Park Service also says that arthropods aerate the soil and shred organic matter into small pieces.

Nematodes add to the nitrogen picture. The PMC review states that nematodes feeding on other organisms take in more N than they need for their body structure. In microcosm experiments, the review reports that soil mineral N levels increase by 20% or more when bacterial- and fungal-feeding nematodes feed. The word microcosm matters here: the result comes from small controlled systems, not from a lawn or a garden bed.

Management can also shift the web. The review describes a case where plots received extra organic matter and were irrigated during the dry post-harvest period. In that case the abundance of fungal- and bacterial-feeding nematodes increased at the time of cover crop incorporation. The review adds that protozoa abundance rose by inference in the same case. In that case, organic matter and irrigation were the inputs.

For a practical view of building organic matter, see how to make garden compost quickly. For checking whether finished compost is ready to add to a bed, see how to know when compost is done. Both articles deal with the inputs, while this one focuses on the organisms.

Where nematodes help and where they harm

The PMC review classifies nematode roles. It says the functional roles of nematodes, determined by their metabolic and behavioral activities, may be categorized as ecosystem services, disservices, or effect-neutral. That framing matters because the same group can help in one setting and cause damage in another.

The review names the main disservices. Among them are overgrazing, which diminishes services of prey organisms, and plant-damaging herbivory, which reduces carbon fixation and availability to other organisms in the food web.

The Park Service gives a shorter version of the balance. Because some nematodes prey on other animals, they can be useful for control of pest insects. The Park Service then adds a caveat in plain words: nematodes aren’t all good. The Park Service also says nematodes can be most easily classified according to their feeding habits.

The review also says that beneficial roles may be enhanced by environmental stewardship that fosters greater biodiversity. It links biodiversity to the complementarity and continuity of the services nematodes provide. The review states that these services depend on continuity, which it links to biodiversity.

Moisture, dryness, and dormancy

Soil moisture controls how the organisms move. The Park Service says that nematodes can’t move through the soil unless a film of moisture surrounds the soil particles. Movement is therefore limited when the soil is dry.

Dry conditions also trigger survival behavior. Under hot, dry conditions, nematodes can become dormant, allowing them to survive long periods of drought. Dormancy is the survival response the Park Service describes for that period.

The Park Service notes that protozoa are tiny single-celled animals that mainly feed on bacteria. The review ties the abundance of protozoa, by inference, to the management case described above, where bacterial- and fungal-feeding nematodes also increased.

How we chose

We picked two sources. The first is a National Park Service page on the soil food web, which covers the main groups and their roles. The second is a PMC review on nematodes in the soil food web, which covers energy flow and nutrient effects. Both pages returned HTTP 200 when checked directly on 2026-10-27, and the quotes in this article come from their fetched text. Retail and product pages were not used.

What we could not verify

The sources describe the web in general terms and in controlled settings. The PMC review’s nitrogen figure comes from microcosm experiments, and it does not transfer directly to a home lawn or a planting bed. The Park Service page is a general overview, so it does not give population counts or the species present in a given soil.

What the sources do not say

The sources do not give the number of organisms in a teaspoon of soil, and this article does not supply one. They do not give a measured food-web size for garden soils. They do not compare soil types in a way that would tell a reader which soil supports the largest web.

Frequently asked questions

What is the soil food web in simple terms?

The National Park Service describes it as the organisms in soil that feed on plants, decaying material, and each other. Its main groups include arthropods, nematodes, protozoa, and the bacteria and fungi that break down organic matter.

Why does energy get smaller at each level of the web?

The PMC review says that carbon and energy dissipate during the course of successive exchanges. Their availability affects how the food web is structured and how its organisms behave.

Do soil organisms make nutrients available to plants?

The Park Service says that soil arthropods help change nutrients into forms available to plants. It also says that increased organic matter concentration and decomposition boost nitrogen and phosphorus levels.

Are all nematodes helpful to plants?

No. The PMC review lists overgrazing and plant-damaging herbivory among the disservices attributable to nematodes. The Park Service says nematodes aren’t all good, though some prey on pest insects.

Why does moisture matter for the soil food web?

The Park Service says nematodes can’t move through the soil unless a film of moisture surrounds the soil particles. Under hot, dry conditions, nematodes can become dormant to survive long periods of drought.

Sources

• National Park Service, White Sands National Park, “Soil Food Web,” https://home.nps.gov/whsa/learn/nature/soil-food-web.htm (HTTP 200, opened 2026-10-27)
• PMC, “Contribution of Nematodes to the Structure and Function of the Soil Food Web,” https://pmc.ncbi.nlm.nih.gov/articles/PMC3380510/ (HTTP 200, opened 2026-10-27)