Soil nematodes: nutrition, balance and feeding groups
Many nematodes consume bacteria, fungi or other organisms and contribute to plant nutrition. Their feeding group helps us understand their role in soil.
Microscopic animals
Nematodes are slender, wormlike animals. In the Soil Biology Primer, Elaine Ingham describes their participation at different levels of the soil food web.
What each group eats
Bacterial feeders eat bacteria; fungal feeders consume hyphae. Predators consume other nematodes and protozoa; omnivores use different foods. Plant parasites feed on roots. Distinguishing these groups matters when evaluating a sample.
Microbial biomass becomes available nitrogen
Nematodes consuming bacteria or fungi release part of the nitrogen as ammonium. Elements held in microbial biomass return in forms plants and other microorganisms can use.
Ingham and colleagues’ research
In a 1985 experiment, Russell Ingham, J. A. Trofymow, Elaine Ingham and David Coleman studied bacteria, fungi and their nematode consumers in controlled soil systems with Bouteloua gracilis. Bacteria plus bacterial-feeding nematodes produced faster plant growth and initially higher nitrogen uptake than bacteria alone.
Adding fungal-feeding nematodes to the fungal system did not similarly increase growth: fungal nitrogen release was already sufficient. The result connects community activity with plant needs and trial conditions.
Predators help regulate populations
Nematode consumers include other nematodes, certain fungi, mites and other groups. UC Davis’s Nemaplex resource explains their contribution to population regulation. Feeding-group diversity and higher-level consumers provide information about food web function.
Water, pores and microscopy
Nematodes move through water films in soil pores. We examine form, mouthparts and other body features to distinguish the five groups, recording observations with sampling conditions.
Following community changes
Nemaplex presents feeding groups as indicators of food web condition. Repeated records help follow responses to interventions. We examine presence and abundance together with other organisms and soil management.
Our field work
We record nematode feeding groups in soil and compost and monitor changes after applications. In the approach taught to us by Dr Elaine Ingham, finding more than one root-feeding nematode per microscope preparation prompts us to examine beneficial organisms and food web balance. We inoculate with suitable soil microbiology with the aim of restoring balance and monitor the results over time.