18.3 Soil and Its Formation

1. 18.3 Soil and Its Formation •Soil Formation •Composition and Characteristics •Interaction between Soil and Climate

2. Soil Formation Weathering occurs by mechanical or chemical means. ex. mechanical—waves on sea cliff chemical—acidic rain on limestone

3. Soil Formation Soil formation occurs from the breakdown of various levels of rock. These rock layers are: Bedrock—the igneous, metamorphic, and sedimentary rock of the lithosphere the may exist as mountains, cliffs, or low-lying plains; provides the material needed to build soil.

4. Soil Formation Parent rock—an area of bedrock that is the source for an area of soil •the lithosphere is the most easily weathered layer. •Mechanical and chemical weathering breakdown the lithosphere into smaller and smaller mineral particles until soil is formed.

5. Soil Formation •This process may take 1,000s of years to form only a few centimeters of soil. • Soil= a mixture of mineral particles, air, water, bedrock, and living and decaying organisms.

6. Soil Formation • Soil forms from the breakdown or weathering of rock. This weathering can be influenced by plants and animals. • Ex. Earthworms breakdown organic material (leaves) and excrete minerals into the soil.

7. Rove beetle Pseudoscorpion Flatworm Centipede Ant Ground beetle Mite Roundworms Adult fly Fly larvae Beetle Springtail Mites Protozoa Millipede Bacteria Sowbug Slug Fungi Actinomycetes Snail Mite Earthworms Organic debris Fig. 10.13, p. 221

8. Soil Formation • Organisms aerate the soil allowing water and gases (like carbon dioxide and oxygen) to reach deeper into the soil and contribute to the weathering process. • Soil profiles are formed as weather progresses.

9. Soil Profiles A horizon= topsoil B horizon= subsoil C horizon=partially weathered bedrock R horizon= bedrock

10. Lords and ladies Oaktree Word sorrel Dog violet Organic debris Builds up Earthworm Grasses and small shrubs Rock fragments Millipede Mole Moss and lichen Fern Honey fungus O horizon Leaf litter A horizon Topsoil Bedrock B horizon Subsoil Immature soil Regolith Young soil Pseudoscorpion C horizon Parent material Mite Nematode Actinomycetes Root system Fungus Red earth mite Springtail Mature soil Bacteria Fig. 10.12, p. 220

11. Composition and Characteristics of Soil Soil is separated into three major texture categories, based upon particle size within it: Sand, Clay, Silt. •Sandy soil •Clay soil •Loam soil

12. Water Water High permeability Low permeability Fig. 10.17, p. 224

13. Sandy Soils • Mineral grains vary in size from 0.05 mm to 2.0 mm in diameter • Have good drainage and aeration, but does not store water well; therefore, it does not suit plants well.

14. Clay Soils • Mineral grains are smaller than 0.002 mm in diameter. • Have poor drainage and no space for air, but hold water very well; not suited for many plants

15. Loam Soils Silt—mineral grains 0.002 to 0.05 mm in diameter •Loam soils consist of roughly equal amounts of sand, clay, and silt particles. •Have excellent ability to hold water and air; due to the even mix of particles, loam is ideal for plant life.

16. Soils and Climate • Because weather has the greatest effect on weathering, climate drastically effects soil formation. • Ex. Desert and Tundra Grasslands Tropical regions

17. Deserts or Tundra • Less water to breakdown bedrock, causing soil particles to be large in size • Strong winds and infrequent rainfall remove lighter, smaller particles, as well. • Soil profiles tend to be only a few mm or cm thick.

18. Grasslands • Weathering of bedrock may occur at a faster rate due to more activity from burrowing plants and animals. • Soil profiles tend to be thicker due to more precipitation.

19. Mosaic of closely packed pebbles, boulders Alkaline, dark, and rich in humus Weak humus- mineral mixture Dry, brown to reddish-brown with variable accumulations of clay, calcium carbonate, and soluble salts Clay, calcium compounds Desert Soil (hot, dry climate) Grassland Soil (semiarid climate) Fig. 10.15a, p. 223

20. Tropical regions • High amounts of rainfall quickly leaches nutrients and small clay particles into the subsoil. • Subsoil is therefore does not have good drainage or aeration. • Thick soil profiles • Nutrients in soil come from the rapid decay of organic materials.

21. Forest litter leaf mold Acid litter and humus Acidic light- colored humus Humus-mineral mixture Light-colored and acidic Light, grayish- brown, silt loam Iron and aluminum compounds mixed with clay Dark brown Firm clay Humus and iron and aluminum compounds Tropical Rain Forest Soil (humid, tropical climate) Deciduous Forest Soil (humid, mild climate) Coniferous Forest Soil (humid, cold climate) Fig. 10.15b, p. 223