Bacteria and fungi digest organic matter and convert it into different
chemical forms that are used by other microbes, invertebrates and plants.
During thermophilic composting the populations of various types of
microorganisms will change as conditions change. The world of microbes in
compost is diverse and mysterious.
The energy that they release during their struggle to stay alive,
creates another ecosystem that helps to further digest and change organic
There is always a challenge in compost in that your mixture produces an
end product that has carbon and nitrogen in balance.
Making compost at the beginning can produce “smells” but once it
gets an “earthy smell” then the compost is ready.
In this lesson we will have the student explore the different microbes
that they can find. It is not
important what their names are, but that students look for organisms that
help this complex chemical process.
Below are some of the organisms the students may see.
Drawing pictures can help them look at the organism careful.
Nematodes, or roundworms, are an abundant
invertebrates in the soil. Typically less than one millimeter in length,
they prey on bacteria, protozoa, fungal spores, and each other. Though
there are pest forms of nematodes, most of those found in soil and compost
Fermentation mites, also called mold mites, are transparent-bodied
creatures that feed primarily on yeast in fermenting masses or organic
debris. Literally thousands of these individuals can develop into a
seething mass over a fermenting surface. As a result, they often become
pest species in fermenting industries, such as wineries and cheese
factories. They are not pests in the compost pile.
Springtails, or collembola, along with
nematodes and mites, dominate in numbers among the soil invertebrates.
They are a major factor in controlling fungi populations. They feed
principally on fungi, but also on nematodes and small bits of organic
Redworms and Earthworms
Redworms and earthworms play an important part
in the break-down of organic materials and in forming finished compost.
Red worms are usually 2-3 inches long and are important in warm composting
debris. The more common
earthworms are important in natural soil.
As worms process organic materials, they coat the material with a
mucus film that binds small particles together into stable
aggregates and helps to protect nutrients from being leached
out by rain. These stable aggregates give soil a loose and well-draining
Ground beetles have many
representatives lurking through litter and soil spaces. Most of them feed
on other organisms, but some feed on seeds and other vegetable matter.
Wolf spiders are truly "wolves" of the soil and
compost communities. They don't build webs, but run freely, hunting their
prey. Depending on the size of the spider, their prey can include all
sizes of arthropods- invertebrate animals with jointed legs and segmented
Centipedes are frequently found in soil and in
compost communities. They prey on almost any type of soil invertebrate
near their size or slightly larger.
students with copies of the organisms used in composting.
Get compost from the
Jora compost and put in petri dishes.
However, if you do not have enough time
One method of collecting
invertebrates is to take grab samples of compost from various locations in
the heap. Some organisms such as centipedes and sowbugs will be more
likely to be found near the surface. Others will be found deeper in the
heap. Spread each compost sample in a large tray or pan, preferably light
in color for maximum contrast. Students should use wooden tongue
depressors, plastic spoons, or other instruments that will not hurt the
organisms, to sort through the compost. Flashlights and magnifying lenses
can be used to enhance the observation. The larger organisms, such as
worms, centipedes, millipedes, sowbugs, earwigs, spiders, ants, beetles,
snails, slugs, some mites, etc., can be observed with the naked eye. To
get a closer look, place samples of the compost in petri dishes or watch
glasses and observe them under a dissecting microscope.
them look at the material and identify different organisms that they find.
You can have them use the work sheet and circle what they see, or
you can give them a blank piece of paper and have them draw what they see
and have them try to identify it with the hand out on microbes
Have the students write down
(on the board) what they are finding. If they find something that is
not on the chart have them draw it, and see if anyone can identify.
Discuss what they have seen.
Refer back to last lab and see if they can figure out what part they play
in the decomposition.