Non-parasitic nematodes are known as free-living nematodes.  These free living nematodes are usually found within the soil and tend to cluster around plant roots.  Free-living nematodes can be categorized as bacterivores, fungivores, predators, and omnivores.

Bacterivores:  Feeds on bacteria. They have a hollow mouth to allow the bacteria to enter the digestive system.

Fungivores. Feeds on fungi.  Use a stylet to pierce the fungi and pull it into the mouth.

Predators. feeds on other nematodes of all types, but of relative size.  Quite rare but can usually be found in the soil.

Omnivores. Very rare, most nematodes are specialized and feed only from specific sources.

Free-living nematodes serve an important role in decomposition.