Soil bacteria: functions and nutrient cycling

Bacteria contribute to decomposition, nutrient retention and cycling, particularly nitrogen, and soil structure. Their relationships with roots and other organisms connect microscopic life with plant nutrition.

Different organisms, different functions

Bacteria are single-celled organisms. Many use root exudates and fresh residues. In the Soil Biology Primer, Elaine Ingham describes decomposers, symbionts, pathogens and groups obtaining energy from inorganic compounds. Each plays a different role.

Nutrients remain within soil life

Growing bacteria incorporate nutrients into their cells, retaining some nitrogen in microbial biomass. Protozoa and bacterial-feeding nematodes consume bacteria and release some nutrients in root-available forms. The Soil Food Web School presents this exchange as a core function: food moves from roots to microbes, and interactions return nutrition to plants.

What Ingham and colleagues found

In 1985, Russell Ingham, Trofymow, Elaine Ingham and Coleman grew Bouteloua gracilis in controlled soil microcosms with low mineral nitrogen, comparing combinations of microorganisms and nematodes. Plants with bacteria and bacterial-feeding nematodes grew faster and initially took up more nitrogen than those with bacteria alone. The researchers related this to nitrogen release and interactions around roots. The result illustrates the potential importance of organisms that feed on microbes under the tested conditions.

Bacterial substances help form structure

Some beneficial bacteria produce sticky substances binding particles and organic material into microaggregates. Fungal hyphae connect these into larger aggregates. Spaces between them accommodate air, water and roots. This links biological activity with structural restoration in the School’s approach.

Bacteria and the nitrogen cycle

Nitrogen-fixing bacteria associated with legumes such as clover convert atmospheric nitrogen into a form the plant can use. Other groups convert ammonium into nitrite and nitrate. With insufficient oxygen, denitrification can turn nitrate into gases, causing nitrogen losses. Community functions therefore depend on aeration, moisture and structure.

Creating conditions for a functioning food web

Cover and residues provide food; reducing compaction supports air and water movement. Caring for the habitat allows microbial communities to grow and interact.

From compost to microscopy

The School connects biologically active compost, liquid applications and microscopic examination. We monitor bacteria alongside fungi, protozoa and nematodes, using the community picture to choose applications and assess responses.

Our field work

We examine soil and compost microbiology in our olive groves and plan liquid extract applications according to food web needs, following our School training.

Sources and further reading

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