Nematodes are nonsegmented, blind roundworms that, along with protozoa, mineralize nutrients containted in bacteria and fungi. These roundworms are the second most dominant form of animal life, next to arthropods. They inhabit surface soils across the world, with higher abundances in sub-Arctic regions (38% of total) than in temperate (24%) or tropical (21%) region, with a total biomass of approximately 0.3 gigatonnes (van den Hoogen et all, 2019).

Some nematodes feed on living plants, especially on their roots, which may hinder plant performance. However, 95% of nematodes are beneficial. Other nematodes eat bacteria or fungi. There are also predator nematodes that feed on protozoa, algae and other small members of the soil food web – grubs, weevils, wasp, even small invertebrates such as slugs.

Mineralization is the most important thing that nematodes do for plant growth. As nematodes need less Nitrogen than protozoa, they release even more immobilized nitrogen into the rhizosphere in ammonium form. If the populations of nitrate-fixing bacteria are low, the mineralized nitrogen remains predominantly in ammonium form.

Compact soils may limit nematodes ability to move and hence diminish Nitrogen available for plants.


Benefits of nematodes for soil and plant health.

Central in maintaining optimal fungi to bacteria ratios
Release Nitrogen, Sulphur, Phosphorus and Carbon contained in microbial bodies
Maintain good soil structure
Feed bacteria and fungi
May help to control slug populations
Nematodes are the abundant in the arctic regions (van den Hoogen et all, 2019)