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Michelle John

on 28 August 2016

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Transcript of Soil

What is soil?

a loose mixture of rock fragments, organic matter, water, and air that can support the growth of vegetation
Soil begins to form when rock is weathered into sediments.
Factors affecting rates of weathering:
1) Rock type- certain rocks are harder to weather than others
2) Climate- rates of weathering are higher in warm, wet areas.
3) Topography
4) Living things
Ice wedging:
a) water enters the rock through cracks
b) changes in temperature
cause rocks to freeze and thaw
c) rock is weathered into sediments
Decomposition and Mixing By Living Things
-Bacteria and fungi are decomposers that live in the soil.
-They break down the remains of plants and animals into HUMUS.
-Humus contains nutrients that plants need to grow.
Burrowing animals mix soil, increasing the
amount of air in the soil and improves the
ability of soil to drain water.
Soil Texture
3 particle sizes: sand, silt, and clay

Sand is the largest particle. It has a coarse texture.

Silt particles are medium sized. They have a silky texture.

Clay particles are the smallest. They have a smooth texture.
Soil Color
-Can give us a clue to the
minerals and organic matter that
make up the soil.
-Brown or black- means soil contains
a lot of humus
-Red- iron minerals
-White- quartz minerals
-Gray- might mean that an area is often wet
- Yellow- might indicate acids that are harmful to plants
-Soils are often a mixture of colors.
Pore Space
-Pore space is the space between
soil particles.
-Water and air moves through these
spaces toward plants
-The best soil for growing most plants
has about 50% of its volume as
pore space.
Soil fertility
-Soil fertility describes how well a
soil can support plant growth.
-Affected by: climate, amount of
humus, minerals, and nutrients.
-In warm, moist climates, deep soils
can develop more rapidly than in cold, dry
Soil profile- a vertical section
of soil that shows layers, called horizons

There are 3 horizons: A, B, and C.
A Horizon
-the topmost layer of soil AKA topsoil
-has more humus than the other layers,
which gives it its dark color
-organic matter such as leaves cover the
surface of the A horizon
B Horizon
-under the A horizon
-contains larger, less weathered
rock fragments and less organic matter
-after rains, water flows downward from
the A horizon to the B horizon, washing
clay and minerals into the B horizon in a
process known as leaching
-leached materials make this layer a
reddish or brownish color.
C Horizon
-underneath the B horizon
-the least-developed layer
-contains the largest rock
fragments and no organic
-solid rock under C horizon
=parent rock
Developed Soil
Undeveloped Soil
Full transcript