Geography Chapter 9: Land and Soil

Chapter 9: Land: How Does It Shape Us?

• This chapter explores how landforms are created and how human activities impact land.
• Earth's surface is dynamic, with forces shaping the ground.
• Topsoil and beach erosion are gradual changes in Earth's surface.
• Climate change contributes to sea level rise and accelerating erosion.
• Soil is a complex mixture of weathered rock, minerals, dead organic matter, and organisms.
• Soil is Earth's skin, but is much thinner than its overall size.
• Soil formation is through processes at Earth's surface where the lithosphere (rocks) and biosphere (life) interact, breaking down rock into particles.
• Air spaces in soil allow water infiltration, promoting aeration.
• Smaller soil particles influence infiltration and nutrient retention.
• Soil texture affects plant growth.
• Soil horizons are layers in soil.
• Soil profiles are cutaway views of soil horizons.
• Soil profiles are typically less than 3 feet deep.

Soil Horizons

• Soil horizons include O, A, B, and C.
• Topsoil (O and A horizons) has complex mixtures of material, including organic matter from living things.
• The O horizon consists of fallen leaves and organic matter (detritus).
• The A horizon is a mix of mineral fragments and organic matter.
• Water infiltrates through the A horizon.
• The B horizon (subsoil) is mainly mineral matter.
• The C horizon consists of weathered parent material (rock or sediment).

What Makes Soil Alive?

• Soil contains diverse life forms, including animals, microorganisms, insects, and worms.
• Nematode worms in soil's upper levels (A horizon) are incredibly numerous (up to 100,000 per cup of soil).
• Nematode worms feed on bacteria and fungi, producing nutrient-rich excrement.
• Earthworms burrow through soil, mixing soil and organic matter, resulting in castings (excrement).
• Soil microorganisms (bacteria and fungi) decompose organic matter.
• Microorganisms return vital nutrients and CO2 to the soil.
• Soil contains significant microorganisms (over 100,000 per cup).

Organic Matter and Soil Structure

• Complex organic compounds in soil are resistant to breakdown, creating humus (dark, sticky organic material).
• Humus enhances water and nutrient retention.

Soil Classification and Factors Affecting Soil Formation

• Biomes are linked to soil orders.
• Specific soil types exist in different regions like deserts.

Topsoil and Plant Growth

• A delicate balance of water, pore space, nutrients, and root space is essential for plant growth.
• Tilth refers to soil properties that facilitate plant growth.
• Topsoil thickens when forming faster than eroding.

Water in Topsoil

• Plants consume water, transporting it from roots to leaves (photosynthesis).
• Water also carries away nutrients (leaching) to deeper layers.
• Salinization (salt build-up) can inhibit plant growth.

Agriculture and Grazing

• Farming often accelerates soil erosion and degrades soil fertility.
• Tillage, overusing fertilizers/pesticides/herbicides, overgrazing, and overirrigation negatively impact soil.
• Sustainable practices enhance soil production and quality (like terracing, cover crops, rotational grazing).

The Erosion of Civilizations

• Plowing can expose soil to erosion.
• Sustainable farming was limited to flat areas like floodplains in ancient times.

Mining

• Mining, although not typically sustainable, can be rehabilitated with practices like importing topsoil to restore degraded landscapes.
• Creating mines in reclaimed areas can help restore biodiversity and create environmental learning environments.

Forestry

• Deforestation (logging/burning) occurs at a global pace of 13 million hectares per year.
• Cutting trees causes soil erosion. Soil binding ability is reduced.
• Steep slopes and excessive harvesting can cause landslides.
• Sustainable forest management can reduce impacts like soil loss.

Urbanization

• Reclamation programs for contaminated sites (brownfields) aim to restore degraded urban areas.
• Sustainable urban design can improve water management (rain gardens) for increased infiltration.

Take-Home Message (Chapter 9)

• Humans' land use (farming, grazing, mining, forestry, urban development) can substantially impact land.
• Regenerative agricultural practices can enhance soil fertility.
• Mining sites can be reclaimed.
• Urban areas can be made more environmentally friendly by using sustainable landscaping and site rehabilitation.