1. What is soil?
Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air.
Lesson 2-1

2. What is soil?
Organic matter is the remains of something that was once alive.
Lesson 2-1

3. What is soil?
Decomposition is the process of changing once-living material into dark-colored organic matter.
Lesson 2-1

4. What is soil? (cont.)
Soil contains gases that fill the soil pores–the small holes and spaces in soil.
pore
from Greek poros, means “passage, way”
Lesson 2-1

5. What is soil? (cont.)
The sizes of pores change with differences in particle size.
Lesson 2-1

6. Formation of Soil (cont.)
Parent material is the starting material of soil.
Lesson 2-2

7. Formation of Soil (cont.)
The average weather of an area is its climate.
If the parent material is in a warm, wet climate, soil formation can be rapid.
Topography is the shape and steepness of the landscape.
Lesson 2-2

8. Formation of Soil (cont.)
The topography of an area determines what happens to water that reaches the soil surface.
Lesson 2-2

9. Formation of Soil (cont.)
Biota is all of the organisms that live in a region.
Biota in the soil help speed up the process of soil formation in various ways.
Organisms can be involved in decomposition of organic matter or form passages in soil for water to move through.
Lesson 2-2

10. Rock and soil are affected by organism activity.
Lesson 2-2

11. Formation of Soil (cont.)
How does biota aid in soil formation?
Lesson 2-2

12. Mature soils develop layers as new soil forms on top of older soil.
Lesson 2-2

13. Horizons
As time passes, weathering is constantly acting on rock and sediment, making soil formation a constant, but slow, process.
Horizons are layers of soil formed from the movement of the products of weathering.
Lesson 2-2

14. Horizons (cont.) horizon
from Latin horizontem, means “bounding circle”
Lesson 2-3

15. Horizons (cont.)
Each horizon has characteristics based on the type of materials it contains.
The three horizons common to most soils are identified as A-horizon, B-horizon, and C-horizon.
The top, organic layer is called the O-horizon and the unweathered, bedrock layer is the R-horizon.
Lesson 2-3

16. Horizons (cont.)
What are soil horizons?
Lesson 2-3

17. Soil Properties and Uses
Lesson 2-4

18. Soil Properties and Uses (cont.)
Lesson 2-4

19. Soil Properties and Uses (cont.)
Some properties of soil can be determined just by observation.
The amount of sand, silt, and clay in a soil can be estimated by feeling the soil.
Many soil properties can be measured more accurately in a laboratory.
Lesson 2-4

20. Soil Properties and Uses (cont.)
Laboratory measurements can determine exactly what is in each sample of soil.
List soil properties that can be observed and measured.
Lesson 2-4

21. Soil Properties and Uses (cont.)
Plant growers can observe how well plants grow in the soil to get information about soil nutrients.
How is soil related to life?
Lesson 2-4

22. The type of soil formed depends partly on climate.
Lesson 2-4