Microfauna – Nematodes
Fungal-feeding nematodes are relatively more abundant in less-disturbed (e.g. notill systems) and perennial systems, where conditions for fungal growth are promoted, than in disturbed systems. Like bacterial feeding nematodes, fungal-feeding nematodes contribute to the process of nutrient mineralization by releasing N and other plant nutrients from consumed fungal tissue. However, in agricultural systems, bacterial-feeding nematodes typically release more inorganic N than fungal-feeding nematodes.
Nematodes as Natural Enemies and Biological Control Agents
Predatory nematodes are of interest because of their role in regulating the populations of other organisms. They generally feed on smaller organisms like protozoa and other nematodes. Thus they can help moderate population growth of bacterial- and fungal-feeding nematodes and protozoa, and help regulate populations of plant-parasitic nematodes.
Insect-parasitic nematodes are species of bacterial-feeding nematodes that live in close association with specific species of bacteria; together, they can infect and kill a range of insect hosts. Insect-parasitic nematodes are available commercially for use in inundative releases to manage the populations of a variety of insect pests.
Most plant-parasitic nematodes feed on the roots of plants. Some species attach to the outside surface of plant roots piercing the root tissue to suck up the cellular content; other species pierce and penetrate the roots of plants, living and reproducing entirely within the root itself. A relatively small number of important plant-parasitic nematode species are known to cause substantial economic damage in cropping systems around the world. The determination of tolerance limits or economic thresholds for plant-parasitic nematodes varies with many factors like species, plant tolerance, and soil type. Because plant parasitic nematodes show varying degrees of host specificity, carefully designed crop rotations are usually a powerful tool for reducing nematode-associated yield losses.
Soil Nematode Communities
The proportions of the different feeding groups in the soil nematode community vary between systems and seasons, and they are influenced by a variety of factors, including crop and soil management practices and the presence and abundance of natural enemies. Management practices like tillage, crop rotation, and the use of organic amendments influence the physical and biological characteristics of the soil that influence the abundance of nematodes. Fungal- feeding, predatory, and omnivorous nematodes are very sensitive to soil disturbances and agricultural systems with fewer physical and chemical disturbances, such as pastures, hay fields, and orchards, tend to support larger populations of these nematodes than more frequently disturbed systems like vegetable- and row-crop fields. On the other hand, tillage and incorporation of organic residues increase the proportion of some bacterial-feeding nematodes often offsetting declines in the numbers of other feeding groups and increasing the total abundance of nematodes. The wide variety of natural enemies that feed on or infect nematodes— predatory nematodes, predatory microarthropods, and nematode-trapping fungi, for example— may have a considerable impact on nematodes in agricultural systems.
Ref: Carmen Ugarte, University of Illinois Ed Zaborski, University of Illinois