Soil Formation, Erosion, Composition and Its Properties

Vocabulary flashcards covering key terms and definitions from the notes on soil formation, erosion, composition, and properties.

Igneous rock

Rock formed directly from cooling magma; classified as basaltic or granitic.

Basaltic

Dark igneous rock rich in iron, magnesium, and calcium; dominant in oceanic crust.

Granitic

Light-colored igneous rock containing feldspar, mica, and quartz; enriched in silicon, aluminum, potassium, and calcium; dominant in continental crust; erosion yields more permeable soils.

Sedimentary rock

Rocks formed by compaction/cementation of sediments; may contain fossils.

Fossils

Preserved remains or traces of ancient organisms within rocks.

Metamorphic rock

Rocks formed from existing rocks under high temperature and pressure, causing chemical and physical changes; examples include slate, marble, and anthracite.

Rock cycle

Geologic cycle of rock formation, alteration, and destruction driven by tectonics, weathering, and erosion.

Physical weathering

Mechanical breakdown of rocks/minerals by water, wind, or temperature changes; increases surface area for further weathering.

Chemical weathering

Chemical breakdown of rocks releasing nutrients; converts primary minerals to secondary minerals (e.g., feldspar to clay, releasing potassium).

Erosion

Physical removal of rock fragments by wind, water, or ice; materials are transported and eventually deposited.

Parent material

Underlying rock from which the inorganic components of soil are derived; different parent materials yield different soils.

Climate (soil formation)

Long-term effects of temperature, humidity, and water on soil development; slow in frozen soils; high-latitude soils often organic; vegetation detritus influences later soil development.

Taiga

Boreal forest region; soils often composed largely of undecomposed organic material in cold climates.

Tundra

Arctic biome with permafrost; soils rich in undecomposed organic material.

Topography

Surface slope and arrangement of the landscape; affects erosion and deposition and thus soil depth.

O horizon

Organic detritus layer (leaves, twigs, bodies) in various stages of decomposition; contains humus.

Humus

Fully decomposed organic matter found within the O horizon.

A horizon

Topsoil; mixture of organic material (humus) with minerals.

E horizon

Leached zone in some acidic soils where iron, aluminum, and organic acids are transported to the B horizon.

B horizon

Subsoil; mineral material with small amounts of organic material; accumulates materials leached from above.

C horizon

Least weathered horizon; lies beneath B horizon and resembles the parent material.

Soil erosion

Process by which topsoil is disturbed or removed by rain or wind; can be accelerated on bare slopes.

Soil texture

Relative proportions of sand, silt, and clay in soil that determine texture.

Sand

Largest soil particle; large pore spaces; drains quickly; easy for roots to penetrate.

Silt

Medium-sized soil particle between sand and clay.

Clay

Smallest soil particle; packs tightly, has low porosity; retains water and nutrients poorly drained.

Porosity

Volume fraction of soil occupied by air or voids; sand textures typically have higher porosity than clay.

Permeability

Ability of water to move through soil; higher in sandy soils and lower in clay soils.

Cation Exchange Capacity (CEC)

Soil’s ability to adsorb and release positively charged ions on clay surfaces; higher with more clay; essential for nutrient availability.

Base saturation

Proportion of soil bases (Ca, Mg, K, Na) to acids; higher base saturation generally indicates higher productivity.

Soil bases

Calcium, magnesium, potassium, and sodium; bases neutralize soil acids and promote plant growth (except sodium in some contexts).

Soil acids

Acidifying constituents (such as hydrogen and aluminum ions) that can hinder plant nutrition.

Fungi

Major group of soil organisms contributing to decomposition and nutrient cycling; part of 80–90% of soil biological activity.

Bacteria

Microorganisms in soil that aid in decomposition, nutrient cycling, and some nitrogen fixation.

Protozoans

Soil-dwelling microorganisms that feed on bacteria and organic matter, aiding nutrient cycling.

Detritivores

Organisms that consume dead organic matter and help recycle nutrients (e.g., earthworms).

Nitrogen fixation

Process by which certain bacteria convert atmospheric N2 into ammonia usable by plants.