Download Uint 2 lesson 5 soil

Unit 2 lesson 5
Soil Formation
https://youtu.be/Y1B1FtHL10k
I. Soil= loose mixture of small rock fragments,
organic matter, water & air
A. What causes soil to form?
1. Weathering of parent rock
a. rocks break into smaller & smaller pieces
b. takes a long time
2. Decomposition & mixing by living things
a. Fungi & bacteria are microorganisms that decompose (break
down) the remains inside the soil
b. humus= remains of pants and animals left behind from
decomposers
c. earthworms and moles burrow through the soil making holes
and increases the amount of air that gets into the soil &
improves drainage
B. Factors that determine how long it takes for
soil to form
1. Parent rock type: some rocks will weather (break apart) faster
than others
2. Climate: Soil develops more quickly in warm, wet areas
3. Topography: soils develop better in flat areas

step slopes lead to erosion
4. Plants and animals: roots


holds soil in place (lessens erosion) allowing soil to form
mixing & decomposition by animals helps to form soil
C. Soil
horizons
1. soil profile: a vertical section of soil that shows all of the
different layers
2. soil horizon: the different physical properties that each
soil profile has
3. The main horizons:
a. A Horizon= The topsoil




Where decomposers live
rich in humus
animal burrows & plant roots
darker in color
b. B Horizon= below A where water
carries minerals
 less humus
 leeching= water carrying
materials through soil
 has a reddish or brownish color
c. C. Horizon= below B and least
developed
 contains large rock fragments
 directly above parent rock
material (rock form which soil
formed from)
Stop and think
1. Your friend tells you that it is very healthy to
have a lot of worms in your garden. Why
would that be?
2. If you drew a bar graph that compared the
amounts of organic matter in each horizon of
soil. What could it look like?
D. Properties of soil
1. Soil Texture= describes the
relative amounts of differently
sized soil particles
a. sand- largest & makes soil feel
course (0.05mm-2mm)
b. silt- smaller than sand &
makes soil feel smooth and
silky (0.002-0.05)
c. clay- smallest & very smooth
or sticky when wet
(>0.002mm)
2. Soil Color= soil color
ranges from brown, black,
red, orange, yellow, grey &
white
a. color indicates the types
and amounts of mineral
& organic matter in the
soil
b. color can indicate if the
soil drains water
3. Soil Chemistry= is determined
by the amount of minerals,
sediment, and organic matter
found in soil
a.
b.
c.
d.
7 = neutral
above 7 (8-14) is basic
below 7 (6-0) is acidic
farmers will add materials to
adjust the pH according to what
they are growing
4. Pore Space= the spaces between
soil particles
a. water & air moves easily through
soils with may well-connected
pore spaces (well drained)
b. best soils have ~50% pore space
with ½ of it water and ½ of it air
4. Soil Fertility= describes how well a soil can
support plant growth
a. factors: climate, amount of humus, minerals,
nutrients, & topography
b. fertile soils have moderate rainfall, flatter land (less
erosion), & are rich in humus
c. farmers add fertilizers to increase the nutrients
Tropical soils
 warm, wet regions
 heavy rains wash
away topsoil=
little humus
 fastest soil
development but
not good for
growing crops
due to heavy
leeching