Nematodes are non-segmented microscopic worms. They are among the most numerous and diverse of the multicellular organisms found on earth.
On average, 1 kg soil comprises about 20,000 nematodes including more than 40 species. For example in the Netherlands, as many as 1000 species are known.
Based on their morphology, it is relatively easy to recognize plant feeders, fungal feeders, bacterial feeders and carnivores. Although plant feeders are often associated with reduced plant growth or plant diseases, the majority of terrestrial nematodes contribute to the recycling of nutrients and thereby to soil fertility.
Thanks to their abundance and high species diversity, nematodes are widely applied as indicators of soil quality. It is very well possible to detect soil pollution and differences in soil fertility based on nematode community analyses.