Soil Biology

Life in the Soil and Landscape

Healthy soil is home to an incredible diversity of living organisms that together form the soil food web.

These organisms range from microscopic bacteria, algae, fungi, and protozoa to nematodes, microarthropods, earthworms, insects, small vertebrates, and plant roots.

As these organisms feed, grow, reproduce, and move through the soil, they help support:

  • Healthy plant growth

  • Nutrient cycling

  • Soil structure

  • Water infiltration

  • Reduced surface runoff

  • Organic matter decomposition

  • Long-term soil health

The soil food web is an essential part of healthy landscapes, turf systems, gardens, and agricultural soils.

How the Soil Food Web Supports Healthy Soil

Soil organisms perform many important functions below the surface.

Bacteria, fungi, and other decomposers break down organic materials such as:

  • Plant residues

  • Manure

  • Dead roots

  • Organic amendments

  • Other biodegradable compounds

This decomposition process releases nutrients and returns them to the soil food web.

Some soil microorganisms also help transform or degrade certain organic contaminants, reducing their persistence under suitable environmental conditions.

Nutrient Cycling and Plant Growth

Soil organisms play an important role in storing, transforming, and releasing nutrients.

Microbial activity can help keep nutrients such as nitrogen within the active soil system rather than allowing them to move rapidly out of the root zone.

Certain bacteria also perform biological nitrogen fixation, converting atmospheric nitrogen into forms that can eventually enter the soil nutrient cycle.

Through these processes, soil microorganisms can improve nutrient availability for grasses, trees, shrubs, flowers, and agricultural crops.

Improving Soil Structure and Water Infiltration

Soil organisms also influence the physical structure of soil.

Fungal hyphae, bacterial activity, plant roots, earthworms, and organic matter all contribute to the formation of stable soil aggregates.

Improved soil aggregation can help:

  • Increase pore space

  • Improve water infiltration

  • Reduce runoff

  • Improve soil aeration

  • Support deeper root growth

  • Improve moisture retention

These characteristics create a healthier root-zone environment and can improve the soil's ability to manage water.

Biological Balance in the Soil

The soil food web also includes organisms that feed on other organisms.

Predatory microorganisms and small soil animals can help regulate populations within the soil ecosystem, including some organisms associated with plant pests and diseases.

This biological interaction contributes to a more balanced and resilient soil environment.

Organisms and Their Interactions

The soil food web describes the network of organisms that spend all or part of their lives in the soil and the movement of energy and nutrients among them.

As one organism consumes another, energy and nutrients move through the food web.

These interactions connect plants, microorganisms, organic matter, and soil animals into a functioning ecosystem.

Primary Producers Begin the Food Web

Most soil food webs are ultimately powered by the sun.

Primary producers such as:

  • Plants

  • Algae

  • Photosynthetic bacteria

  • Mosses

  • Lichens

use sunlight to capture carbon dioxide and produce carbon-rich organic compounds.

These materials provide energy that eventually becomes available to many other organisms in the soil ecosystem.

Plant roots also release carbon-rich compounds into the surrounding soil, helping support microbial activity within the rhizosphere.

Microorganisms Use Different Energy Sources

Many soil microorganisms obtain energy by consuming organic carbon.

However, some bacteria known as chemoautotrophs obtain energy by oxidizing inorganic compounds containing elements such as:

  • Nitrogen

  • Sulfur

  • Iron

These microorganisms contribute to important nutrient transformations within the soil.

Decomposition Makes Nutrients Available

As microorganisms decompose plant residues, organic matter, and other biological materials, nutrients are transformed from one form to another.

Some of these nutrients eventually become available for uptake by plant roots or use by other soil organisms.

This continuous recycling process is one of the most important functions of the soil food web.

Plants and Soil Microorganisms Work Together

Plants and soil organisms interact continuously.

Growing roots release sugars, organic acids, amino acids, and other compounds into the surrounding soil.

These root exudates provide food for microorganisms living near the root surface.

In return, soil organisms can support plant growth by:

  • Decomposing organic matter

  • Cycling nutrients

  • Improving soil aggregation

  • Supporting root-zone structure

  • Competing with certain plant pathogens

  • Helping maintain biological balance

These relationships make the root zone one of the most biologically active areas of healthy soil.

Building a Healthy Soil Food Web

Healthy landscapes begin below the surface.

Maintaining organic matter, reducing unnecessary soil disturbance, improving aeration, managing irrigation, and supporting diverse microbial populations can all contribute to a stronger soil food web.

A biologically active soil can provide better conditions for root development, nutrient availability, water movement, and long-term plant health.