Nematodes are microscopic
threadlike organisms which form part of the soil food web; in fact the word
nematode comes from the Greek word meaning thread. Nematodes in the soil are
grouped into two classes: free living nematodes (the good) and parasitic
nematodes (the bad). The parasitic nematodes are those that attack plant roots
and cause diseases, while free living nematodes refer to those that are
beneficial in the soil. Because of the harmful impact parasitic nematodes have,
a lot more research has been done on them than on the free living ones. This
blog however will focus more on good nematodes.
These nematodes can be
studied and their presence in the soil can tell you about the abundance of
other microbes such as bacteria, fungi and other nematodes. This is due to the
fact that most of the nematodes in this group have a very strict diet. Bacterial
feeders/grazers, otherwise known as bacterivores, only feed on bacteria; fungi grazers
(fungivores) only feed on fungi, while predatory nematodes feed on protozoa and
other nematodes. For example, soil that has a high bacteria population is most
likely to have an abundance of bacterivorous nematodes. It is important that a
soil food web contains all of these types of nematodes, especially the
predators, in order to maintain the balance. Predatory nematodes act as
biological control agents by controlling the bacterial and fungi populations in
the soil, ensuring that over-feeding of bacteria and or fungi by other
nematodes or protozoa is avoided. Another important role of free living
nematodes is their ability to revive old and inactive bacterial or fungal colonies.
Nematodes do this by carrying them to fresh organic material which provides easily
digestible food thereby giving these microbes a better chance of being
Nematodes don’t move much in
soil as they have been reported to only move no more than 1 meter in their
entire life cycle. The major way in which they spread in a field is through
tillage which could possibly lead to nematode infestation, especially if the
nematodes being spread are the bad ones. There are 2 ways in which they can
spread through tillage: 1) transference of their eggs by wind to other parts of
the field, and even to neighbouring farms, induced during tillage; 2)
transference by the tillage implement to other parts of the field.
These types of nematodes are
a nightmare to deal with because they can cause very serious plant diseases.
These nematodes puncture the plant roots and suck out fluids from the plant
causing the plant to wilt. When a nematode attacks the plant it opens up the
plant to all sorts of vulnerabilities. The plant’s defence system is weakened,
causing it to be susceptible to attacks from other bad microbes and pests. Farmers
should be careful not to implement management practices that could cause the possible
spread of bad nematodes in their fields, especially because the infestation of
the bad nematodes is very difficult and expensive to control.
The role played by nematodes
is important in the soil. Not only are they critical in maintaining balance of
the food web but also their presence in the soil provides an ability to
estimate the amount of other microbes. It is however important that further
research is carried out in order to better understand the role of good
nematodes in the soil ecosystem.