1. Soil and Its Uses

2. 13.4 Soil Formation Soil forming factors include the following:
Parent Material
Climate
Topography
Biological Factors
Time

3. 13.4 Soil Formation
Soil formation begins with fragmentation of parent material.
Parent material consists of ancient layers of rock, or more recent deposits from lava flows or glacial activity.
The first organisms to gain a foothold in modified parent material also contribute to soil formation.
Lichens form pioneer communities.
Decomposition of dead lichens further alters underlying rock.

4. 13.4 Soil Formation
Humus is the organic material resulting from the decay of plant and animal remains.
It mixes with top layers of mineral particles, and supplies needed nutrients to plants.
It creates a crumbly soil that allows adequate water absorption and drainage.
Burrowing animals such as earthworms bring nutrients up from deeper soil layers, improving soil fertility.

5. 13.5 Soil Properties
Soil texture is determined by the size of mineral particles within the soil.
Too many large particles (sand, gravel) lead to extreme leaching.
Too many small particles (clay) lead to poor drainage.

6. 13.5 Soil Properties
Soil texture

7. 13.5 Soil Properties
Soil structure refers to the way various soil particles clump together.
An ideal soil for agricultural use is loam, which combines the good aeration and drainage properties of large particles with the nutrient retention and water-holding ability of clay particles.
In good soils, one-half to two-thirds of spaces contain air after excess water has drained.
A good soil is friable, which means that it crumbles easily.
Protozoa, nematodes, earthworms, insects, algae, bacteria, and fungi are typical inhabitants of soil.

8. 13.6 Soil Profile
The soil profile is a series of horizontal layers of different chemical composition, physical properties, particle size, and amount of organic matter.
Each recognizable layer of the profile is known as a horizon.

9. 13.6 Soil Profile
O horizon is made of litter, undecomposed or partially decomposed organic material.
A horizon is the topsoil, or the uppermost layer. It contains most of the soil nutrients and living organisms.
E horizon is formed from leaching darker materials.
Usually very nutrient poor.

10. 13.6 Soil Profile
B horizon is the subsoil. It contains less organic matter and fewer organisms, but accumulates nutrients leached from topsoil. It is poorly developed in dry areas.
C horizon is weathered parent material.
R horizon is bedrock.

11. 13.6 Soil Profile

12. 13.6 Soil Profile
Over 15,000 separate soil types have been classified in North America.
Most cultivated land can be classified as either grassland or forest soil.
Grassland soils usually have a deep topsoil layer. A lack of leaching results in a thin layer of subsoil.
In forest soils, which are typically high rainfall areas, the topsoil layer is relatively thin, but topsoil leachate forms a subsoil that supports substantial root growth.

13. 13.6 Soil Profile
Major soil types