Investigating Soil
MARCH 2014
Riverina Environmental Education Centre
Table of Contents
1.
2.
3.
4.
5.
6.
7.
Important Stuff
What is soil?
Describing soil
Soil Erosion
Soils and Farming
Soil Bugs
Investigating: soil erosion
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1. Important Information

Soil contains broken down rock, dead animals and plants, live animals and
plants, air and water. They are all important for healthy soil.

Plants obtain most of their nutrients from soil.

We depend on many plants for food such as wheat for bread so we depend
on the soil for our food.

Soil can lose its ability to help grow healthy plants (soil degradation) if we do
not care for it.

Rocks break down very slowly to help form soil.

Soil is lost through erosion.

Many Australian soils are very shallow so we can't afford to lose it through
erosion.
2. What is soil?
Layers
Soil is made of:
Topsoil has
many nutrients
and plant roots
Broken down rock (minerals)
Dead animals and plants
Living animals and plants
Water
Subsoil has clay
and holds more
moisture
Air
Weathered rock
Rock
Rock
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3. Describing soil
Horizons
Soil usually changes from the
surface down to the bottom.
Different layers, called horizons,
can be seen in the diagram (top
soil and sub-soil). Each horizon can
be described using the following
features.
Colour
Topsoil: darker colours
(browns/blacks) indicate more
humus is present (broken down
plant matter).
Sub-soil: red, orange and grey
indicate whether the soil is in a dry
or moist area. Iron in the clay
changes colour depending on
whether it is dry (red) or moist
(yellow to grey).
Slaking
Indicates the stability of soil in water and whether it is
an erosion hazard. To test take a dry, pea size sample
of soil, place it in a dish of water and observe it for one
minute. If the aggregate falls apart it slakes, if it stays
together it does not slake and is stable in water. The
sample must be dry or the test will not work.
Texture
This is the size of mineral particles in the soil, sand, silt and clay.
Take a hand full of soil, crush it, remove any rocks
and slowly add water while needing it in your hand
until it is just sticky. Form a ball and then squeeze the
soil between your thumb and finger to produce a
ribbon of soil. Keep pushing the soil out with the
thumb until the ribbon breaks. The length of ribbon
indicates the soil texture.
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4. Soil Erosion
Erosion is the removal of soil
by water and wind.

Moving water can pick
up soil particles and
wash them away.

Rain drops landing on
bare soil are like small
bombs and blast the
soil apart.

Water flowing over bare
soil can pick up soil
particles and wash
them away causing
gullies to form.
Photo: erosion gully
near Lake Albert, Wagga Wagga.

Wind can pick up soil and blow it away. In really bad dust storms, some of our
soil has landed in New Zealand.
Photo: dust storm near Wagga Wagga- John Rodham
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5. Soil Degradation
Soil degradation occurs when soils get "sick" because of poor management by
people. The result can be soil erosion, low fertility or very acid soils. This can occur
because:

ploughing the land breaks up the natural soil clumps;

soil animals such as earth worms are killed by chemical sprays;

too much fertiliser and some plants make the soil acid; and

hard hoofed animals compact the soil reducing the number of holes for air and
water to circulate.
pH
Indicates weather the soil is acid or alkaline. If the soil is too acid, some nutrients
cannot be taken up by the plants and they will not be healthy.
Soil acidity test, called a pH test.





Take half a teaspoon of crushed soil.
Add 3 drops of universal indicator which
changes colour depending on soil acidity.
Sprinkle with barium sulphate, a white,
neutral powder which absorbs the indicator
and shows the colour better.
Wait 2 minutes for the colour to develop and
compare with the colour card.
Numbers below 7 are acidic. If the acidity is
in the yellow range or lower the soil may be
too acidic for healthy plants.
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6. Soils and farming
Breaking up the natural chunks of soil (structure) by ploughing destroys the natural
cracks and holes through which air and water pass. It also destroys the habitat of
many important soil organisms such as earth worms.
Compare the two photos showing old and new farming methods. In the top photo the
soil is being prepared for sowing the crop. In the bottom photo the seeds are being
sown directly into the stubble of the previous crop.
What is happening to the soil and soil organisms in each photo?
Left photo courtesy Dept. Infrastructure, Planning & Natural Resources. Photo at right courtesy John
Deere.
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7. Soil bugs (Soil fauna)
Animals living in the soil have very important jobs:

they burrow through the soil creating holes for air and water to enter;

they eat leaf litter and dead animals returning the nutrients back into the soil.
Larger soil animals
Flat cockroaches live in leaf
litter in colonies with a few
friends and communicate
using scent.
An important farm worker helping to
keep the soil healthy. Numbers are
declining with the use of poison
sprays and chemical fertilisers.
Millipedes hate light and hide
under leaf litter or burrow into
the soil. They are almost blind.
They eat plant material.
Smaller soil animals seen under the microscope
These little soil animals can be seen under the microscope, especially in compost. They are less
than one millimetre long. Photos: CSIRO
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