Nematodes are small, non-segmented worms a few millimetres long. They live in the water films around soil particles. Because there are a number of plant-parasitic species, nematodes have a bad reputation as they can seriously hamper plant growth.

However, most species are useful for maintaining soil quality. A teaspoon of healthy soil contains several dozen nematodes. A healthy tillage layer contains 4 to 10 million of them per square metre. Nematodes are divided into food groups: bacterivores, fungivores, carnivores, omnivores and herbivores. In less disturbed soils, the likelihood of carnivorous nematodes is higher than in intensively cultivated soils.

The main functions of nematodes are:

  • “grazing” on fungi and bacteria, releasing nitrogen and phosphorus
  • disease resistance: fungal-feeding nematodes and predatory nematodes play a part in this. ​