Soil organism diversity
As well as microorganisms such as fungi, bacteria
and protozoa, a healthy grazing topsoil should
contain a diverse range of larger organisms and
insects.
These include earthworms, dung beetles,
springtails, ants, nematodes, mites, potworms,
millipedes and a range of other insects.
Many of these are visible to the naked eye. These
larger organisms are called soil invertebrates or
soil organisms.
Why it is important:
A diversity of soil organisms is important to soil
health in a number of ways. All soil organisms
are important in helping to break down organic
matter and cycling nutrients in the soil.
Some, such as earthworms and dung beetles, also
have a positive influence on soil structure and
water infiltration. Although some soil organisms
No legs
feed on living plant roots, and are pathogens,
most do not. In fact many soil organisms are
predators of pathogens and can keep those
populations under control.
Generally the more diverse the community
of soil organisms, the more effective nutrient
cycling, soil structure maintenance and disease
suppression will be.
How to assess it:
Soil organism diversity can be assessed by
counting the number of different types of
organisms seen in a soil sample in a set period.
Taking a sample of topsoil from an intact soil
cube, the soil organisms can be observed with
the naked eye or with the aid of a hand lens, or
magnifying glass. Make a note of each different
type of organism seen.
A simple way to identify organisms in the soil is
by two characteristics – its size (less than 1mm,
1mm-5mm and bigger than 5mm) and the
number of legs (none, six, eight or many).
Six legs
Eight legs
Many legs
* Drawings not to scale
Paurapod
What is it?
1mm-5mm
Potworm
Mites
Termite
Centipede
Soldier fly
Soldier
larvae
* Drawings
not fly to
scale
Millipede
Beetle
Ant
Measuring method
At a minimum, soil organism diversity can be
assessed at one point along the transect. Use the
same sample of soil collected to assess aggregate
strength. Alternatively, walk 15 paces along the
transect and, using the spade, dig out an intact
sample. Try to keep it intact as a cube and at least
10cm deep if possible. If the monitoring point
consists of a high tussock grass or shrub, take the
18 - RASH MANUAL
Symphylan
Earthworm
sample adjacent to the plant. From the sample,
carefully slice off the top 5cm layer with a spade.
Keep this top layer. Divide it in half. Keep one half
– this will be the sample. Evenly spread it out on a
flat board or plastic tray.
Equipment:
Spade, tray or board, magnifying glass or hand
lens, RASH Soil Organisms ID Chart or Field Guide
to Insects, stopwatch or smartphone.