Are soil nematodes beneficial or harmful?
The majority of soil nematodes are beneficial to soil health and the environment.
Nematodes are often talked about in a quiet fearful voice. The image of the small microscopic worms can bring grown men to their knees. Unfortunately like many things in our world, a few “bad” apples have ruined the entire bushel. Attention has been given extensively to a small segment of the nematode population that negatively impacts crops but those nematodes are a very small percent of the nematode population. The larger percentage of the population benefit agriculture and the environment especially soil health.
Nematodes enhance soil quality in four major areas: regulate the populations of other soil organisms, mineralize nutrients into plant-available forms, provide a food source for other soil organisms and consume disease-causing organisms.
Nematodes are considered grazers. They move through the soil profile devouring smaller organisms as well as distributing any bacteria or fungi that are on them as well as any that are in their digestive system. If the nematode population is low, they will stimulate the growth rate of prey populations. If the nematode population is high, they have the potential to have negative impact on soil health by devouring too much of their prey especially micorrhizal fungi. There are also predatory nematodes that balance the population of other nematodes
Nematodes are important nutrient mineralizers. When nematodes consume bacteria or fungi they release excess ammonium (NH4+). Bacteria and fungi both have more ammonium than what the nematode needs so the extra is released in a plant available form.
Nematodes are not the highest organism in the soil food web. Soil microarthropds and insects as well as bacteria and fungi feed on nematodes. As stated earlier there are also predatory nematodes in the soil that consume nematodes.
A major function of soil nematodes is that they are biocontrol agents, meaning they can be used to eliminate disease causing nematodes and other organisms. This trait causes predatory nematodes to be a great resource in the battle against soil borne diseases.
For more information on nematodes and how they impact soil health obtain a copy of the “Soil Biology Primer” published by the Soil and Water Conservation Society. For more information on how to build soil download “Building Soil for Organic and Sustainable Farms” from Michigan State University Extension.