1. Soil Formation https://youtu.be/Y1B1FtHL10k
Unit 2 lesson 5
Soil Formation

2. I. Soil= loose mixture of small rock fragments, organic matter, water & air A. What causes soil to form?
Weathering of parent rock
rocks break into smaller & smaller pieces
takes a long time
Decomposition & mixing by living things
Fungi & bacteria are microorganisms that decompose (break down) the remains inside the soil
humus= remains of pants and animals left behind from decomposers
earthworms and moles burrow through the soil making holes and increases the amount of air that gets into the soil & improves drainage

3. B. Factors that determine how long it takes for soil to form
Parent rock type: some rocks will weather (break apart) faster than others
Climate: Soil develops more quickly in warm, wet areas
Topography: soils develop better in flat areas
step slopes lead to erosion
Plants and animals:
roots holds soil in place (lessens erosion) allowing soil to form
mixing & decomposition by animals helps to form soil

4. C. Soil horizons
soil profile: a vertical section of soil that shows all of the different layers
soil horizon: the different physical properties that each soil profile has
The main horizons:
A Horizon= The topsoil
Where decomposers live
rich in humus
animal burrows & plant roots
darker in color

5. B Horizon= below A where water carries minerals
less humus
leeching= water carrying materials through soil
has a reddish or brownish color
C. Horizon= below B and least developed
contains large rock fragments
directly above parent rock material (rock form which soil formed from)

6. Stop and think
Your friend tells you that it is very healthy to have a lot of worms in your garden. Why would that be?
If you drew a bar graph that compared the amounts of organic matter in each horizon of soil. What could it look like?

7. D. Properties of soil
Soil Texture= describes the relative amounts of differently sized soil particles
sand- largest & makes soil feel course (0.05mm-2mm)
silt- smaller than sand & makes soil feel smooth and silky ( )
clay- smallest & very smooth or sticky when wet (>0.002mm)

8. Soil Color= soil color ranges from brown, black, red, orange, yellow, grey & white
color indicates the types and amounts of mineral & organic matter in the soil
color can indicate if the soil drains water

9. Soil Chemistry= is determined by the amount of minerals, sediment, and organic matter found in soil
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

10. Pore Space= the spaces between soil particles
water & air moves easily through soils with may well-connected pore spaces (well drained)
best soils have ~50% pore space with ½ of it water and ½ of it air

12. Soil Fertility= describes how well a soil can support plant growth
factors: climate, amount of humus, minerals, nutrients, & topography
fertile soils have moderate rainfall, flatter land (less erosion), & are rich in humus
farmers add fertilizers to increase the nutrients

13. 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