Bacteria & Fungi in the Soil

Many different microorganisms live in the soil including bacteria and fungi. A single handful of soil is likely to contain thousands of different species of bacteria along with hundreds of species of fungi and nematodes. Microorganisms are essential to the life-giving properties of soil. Most bacteria and fungi live in the top few inches of soil where organic matter is present.

Microorganisms in the soil are critical for soil quality. Different types of bacteria have an important role in decomposing organic material. In later stages of decomposition, this role is dominated by fungi. Decomposition affects plant growth and the amount of pollutants in the environment. Bacteria and fungi also protect crops from diseases and pests.

Bacteria are minute one-celled organisms. Most are decomposers that consume carbon compounds and convert energy into useful forms, according to the U.S.D.A. Natural Resources Conservation Service. Some types of soil bacteria are called mutualists. These are bacteria that form partnerships with plants. Some mutualists extract nitrogen gas from the air and convert it into forms that can be used by plants. Other types of bacteria are pathogens, while a fourth group obtains energy from sources besides carbon compounds and aid in decomposition of pollutants.

Fungi in soil function along with bacteria to perform important roles within the soil. Examples of these functions include disease suppression and water dynamics. According to the U.S.D.A. Natural Resources Conservation Service, there are three groups of fungi categorized based on how they get their energy. Decomposers convert dead organic matter into forms that can be used by other organisms. These bacteria are essential in decomposing pollutants. Mutualists help bring soil nutrients to plants. The other group of fungi consists of parasites or pathogens. Some cause agricultural losses, while others feed on nematodes and insects.

The work of bacteria and fungi and the interconnectedness between them is very complex. Combinations of soil bacteria change quickly depending on time of year, temperature, the amount of moisture in the soil and type of crop. Populations of bacteria are reduced by dry conditions, lack of organic matter and acidity. Healthy amounts of soil bacteria are encouraged by organic matter and ground cover, such as grass or mulch. Fungi have advantages over bacteria in dry conditions. When it’s dry, fungi can grow and survive, even when the moisture level is too low for bacteria to be active.