1. Lesson 6
Soil

2. Can plants be grown in pure sand?
Think About It…
Can plants be grown in pure sand?

3. How does soil form and how can it be preserved?
Focus Question…
How does soil form and how can it be preserved?

4. Development of Soil… What is the first step in soil formation?
 The weathering of rocks
Weathered rocks and the Koevals!

5. Development of Soil…
Mosses and lichens are called pioneer organisms because
 they are the first organisms to grow on rocks

6. Development of Soil…  the addition of humus (decaying organic matter)
2. What is the second step in soil formation?
 the addition of humus (decaying organic matter)

7. Soil Profile – Draw this!
A soil profile is a cross section of soil.
There are three major soil horizons – A, B, and C.
Horizon A – top & darkest layer (high concentration of organic matter - humus)
Horizon B – subsoil enriched with clay minerals leached from the topsoil.
Horizon C – bottom layer (weathered rock)

8. Factors Affecting Soil Profiles
1. Topography (slope) of the land –
Soils on slopes tend to be thinner
soils in flat areas like valleys or plains are thicker
Age – older soils are thicker because they have had more time to develop.
Climate – See next few slides…

9. Climate Affects Soil: Tropical Soil
a. Tropical Soil…
Is intensely weathered (and often infertile) soil because of …high temperatures and heavy rainfall
Can only be farmed for a few years

10. Climate Affects Soil : Desert Soil
Climate Affects Soil : Desert Soil
b. Desert soil…
Is light-colored with a thin A horizon b/c…
contains little or no organic matter b/c there is very little rain.

11. Cryptobiotic Crust – Don’t Bust the Crust!
gwsedona/department/10/crust_300.jpg

12. Climate Affects Soil : Polar Soil
Polar Soil has permanently frozen soil (permafrost) b/c
It forms at high latitudes and elevations so it is always cold!
Can not support the growth of trees (tundra)

13. Climate Affects Soil: Temperate Soil
Temperate soil is rich and thick and very fertile because
 it forms in flat areas over a long period of time
Includes grasslands, forests, prairies
Our grains are grown here!

14. Distribution of Soil Types
Distribution of Soil Types

15. Soil Textures Particles of soil are classified by size.
Soil Textures
Particles of soil are classified by size.
The particles of soil are…
 clay, silt, & sand.
What determines a soil’s texture
 The relative proportions of these particles.
The texture of a soil affects
 its capacity to absorb and retain water & support plant growth.

16. Soil Texture Triangle

17. It is used in conventional farming
Soil Fertility…
Soil fertility is the measure of a soil’s ability to grow plants.
Farmers use fertilizer to… replace nutrients & grow more food.
Inorganic fertilizer is made in factories.
There are 2 disadvantages:
requires energy to make it.
too expensive for poor farmers.
It is used in conventional farming
Fertilizer factory in Japan

18. 2b. Natural, Organic Fertilizer…
2b. Examples: compost (plants) and manure (animal waste)
The advantage of using organic fertilizers…
… adds humus and moisture to the soil
Manure-spreading Truck

19. Soil Fertility - Legumes
The planting of legumes – peas, beans - and clover – allows bacteria to grow on plant roots and replace nitrates in the soil.
Nitrogen-fixing bacteria… get nitrogen (N) from the air and “fix” it into fertilizer.
Remember this for your lab!!
Note the nodules on the roots – these contain colonies of nitrogen-fixing bacteria.