Chapter 2, Comprehensive Pedology: Soil Formation, Types, and Horizons

Chapter 2

What is pedology?

The study of soil formation, classification, and mapping.

Who laid the foundation of pedology in 1883?

V.V. Dokuchayeva.

What are the five key soil-forming factors?

Parent material, climate, life, topography, and time.

What is a pedon?

A manageable unit of soil study, approximately 1m x 1m x 1.5m, extending from the surface to the depth of deepest root growth.

What is a polypedon?

A collection of pedons grouped into soil series.

What initiates soil formation on bare rock?

Lichens colonizing the rock.

What processes contribute to physical weathering?

Temperature, ice, water, and wind.

What is chemical weathering?

The alteration of minerals through processes like dissolution, hydrolysis, hydration, and oxidation-reduction.

How do plants promote weathering?

Through root pressure and acid secretion.

What is the original source of most soils?

Rock.

What are the three main types of rocks?

Igneous, metamorphic, and sedimentary.

How do igneous rocks form?

From the solidification of magma or lava.

What distinguishes intrusive igneous rocks?

They form from slow cooling of magma.

What distinguishes extrusive igneous rocks?

They form from rapid cooling of lava.

What is the composition of granite?

Coarse-grained, light colored, composed of feldspar and quartz.

What is the composition of basalt?

Fine-grained, dark colored, rich in iron and calcium.

Which type of rock is the foundation of Earth's crust?

Igneous rock.

What is the texture of sedimentary rocks?

Crumbly and layered.

What is the significance of darker igneous rocks?

They weather more easily and provide more nutrients.

What is soil genesis?

A dynamic process linking geology, biology, and climate.

What is the role of climate in soil formation?

It is one of the five key soil-forming factors.

What does the term 'weathering' refer to in soil formation?

The process by which rocks break down into soil.

What are the two main types of igneous rock formation?

Intrusive forms from magma underground with slow cooling and large crystals; extrusive forms from lava on the surface with rapid cooling and small or glassy crystals.

How does weathering of igneous rocks contribute to soil?

It contributes to soil fertility and texture.

Which igneous rock weathers faster, basalt or granite?

Basalt weathers faster.

What does granite weather into?

Granite weathers into acidic, sandy parent materials.

What mineral is resistant to weathering and weathers slowly into sand?

Quartz.

What does feldspar weather into?

Feldspar weathers into clay.

What percentage of Earth's surface is covered by sedimentary rock?

About 75%.

How are sedimentary rocks formed?

They are formed from mud, sand, or other materials deposited by water, wind, or gravity and cemented into rock by pressure or chemical processes.

Name two common parent materials of American soil.

Sandstone and limestone.

What causes metamorphic rocks to form?

They form when igneous or sedimentary rocks are exposed to great heat and pressure.

What does limestone turn into when metamorphosed?

Limestone turns into marble.

What is the outcome of sandstone when it undergoes metamorphism?

Sandstone turns into quartzite.

What happens to granite during metamorphism?

Granite turns into gneiss.

What are residual soils?

Soils that form directly from weathered bedrock in place.

What is glacial drift?

Parent materials created by glaciers that have picked up and transported clay, sand, rocks, and other materials.

What is glacial till?

Debris dropped directly in place by glaciers, forming dense layers and hardpans.

What are moraines?

Hills formed from till deposited at glacier margins.

What is glacial outwash?

Material carried by ice but sorted by water as it rushes out of the glacier.

What are alluvial soils?

Soils formed from materials carried and deposited by moving freshwater, often found in rivers and floodplains.

What is an alluvial fan?

A fan-shaped deposit formed where parent materials are carried and deposited by downslope streams.

What are deltas?

Landforms that develop where a river enters the ocean and slows, depositing fine particles.

What characterizes lacustrine deposits?

Deposits formed in still freshwater, often sandy on shorelines and with poor natural drainage.

What is colluvium?

Material generated by the force of gravity causing things to roll downhill.

What is loess?

Wind-blown silt deposits that are fertile but highly erodible.

What defines organic soils?

Soils that contain 20% or more organic matter.

What is the impact of climate on soil formation?

Climate influences temperature and moisture, affecting soil properties and formation processes.

What drives soil formation and development?

Precipitation drives soil formation and development.

How does temperature affect soil weathering?

Warmer soils weather faster.

What role does water play in soil weathering?

Water enables key weathering reactions and frost wedging.

What happens to soluble materials in soil due to percolating water?

Percolating water leaches soluble materials and translocates fine particles.

What is a characteristic of desert soils?

Desert soils tend to accumulate salts.

How do humid regions affect soil organic matter?

Humid regions support more vegetation and have higher organic matter in topsoil.

What type of soils do grasslands produce?

Grasslands produce mineral soils with the highest organic matter.

Where is most biomass stored in forests?

Forests store most biomass aboveground.

What is the relationship between topography and soil development?

Topography influences soil development primarily through water movement and wetness.

What is the water table like at different slope positions?

The water table is deepest near the shoulder and closest to the surface at the base and in depressions.

How do depressions affect soil characteristics?

Depressions collect water, are very wet, and tend to receive eroded materials, developing finer textures.

What is the impact of time on soil characteristics?

Soils change over time, with young soils typically low in nitrogen and high in phosphorus.

How does soil aging differ in various climates?

Aging is fastest in warm, humid climates and slowest in cold, dry, or weathering-resistant settings.

What are the four soil-forming factors?

Additions, losses, translocations, and transformations.

What is caliche?

Caliche is a hard subsoil layer cemented by lime, formed through processes of addition, translocation, and transformation.

What are the master horizons in soil?

The master horizons are O (organic layer), A (topsoil), E (eluviation), B (subsoil), C (parent material), and R (bedrock).

What does the A horizon represent?

The A horizon is the surface mineral horizon enriched with organic matter.

What is the role of the B horizon?

The B horizon is the zone of accumulation where materials leached from A and E horizons gather.

What is the solum?

The solum is the portion of soil actively altered by soil-forming processes, typically containing most plant roots.

How are transitional horizons identified?

Transitional horizons are identified by two master letters, with the dominant one written first.

What does the suffix 'Ap' denote in soil horizons?

'Ap' denotes a surface layer disturbed by human activity.

What does 'Bt' indicate in the B horizon?

'Bt' indicates the B horizon where clay has accumulated by illuviation.

What is the significance of numeric suffixes in soil horizons?

Numeric suffixes subdivide horizons into distinct layers.

What is the typical depth of the Ap horizon due to cultivation?

The top 7 inches are typically classified as Ap due to cultivation.

What happens to the A horizon below the Ap layer?

The A horizon continues below Ap and is split into A1 and A2.

What is the appearance of the Bw horizon?

The Bw horizon is weakly developed and appears lighter than A and darker than C.