DYA10243 Soil Science - Chapter 1: Introduction to Soil

Flashcards covering the fundamentals of Soil Science, including definitions, composition, weathering processes, formation factors, and soil horizon characteristics.

Soil (General Definition)

The upper layer of earth in which plants grow, typically consisting of a mixture of organic remains, clay, and rock particles.

Soil (Scientific Definition)

A natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface.

Soil Minerals

Inorganic materials divided into three size classes: sand, silt, and clay.

Soil Texture

The percentages of particles in the three size classes (sand, silt, and clay) found in a soil sample.

Average Soil Composition (Solids)

Accounts for $50\%$ of soil volume, consisting of $45\%$ inorganic mineral materials and $5\%$ organic matter.

Average Soil Composition (Pore Space)

Accounts for $50\%$ of soil volume, consisting of $25\%$ water and $25\%$ air.

Soil Weathering

The process in which rocks and minerals undergo disintegration and decomposition due to reaction with air, water, and living organisms to form soil.

Physical Weathering

The disintegration of rocks and minerals into smaller sizes caused by temperature changes without changing the chemical composition.

Abrasion

A type of physical weathering where rocks collide or rub against one another due to the action of wind and water.

Freeze-thaw

A physical weathering process where water expands upon freezing, causing rocks to break apart.

Exfoliation

The development of cracks parallel to the land surface due to pressure, eventually causing rock layers to peel off.

Chemical Weathering

Processes that dissolve or change minerals through chemical reactions with water, gases, and solutions to form new minerals.

Oxidation

A chemical weathering reaction where oxygen combines with iron-bearing silicate minerals to cause "rusting."

Hydrolysis

The breakdown of rock by acidic water to produce clay and soluble salts.

Biological Weathering

The breakdown and alteration of rocks and minerals caused by the effects of living organisms like lichens, fungi, and plant roots.

Parent Material

The primary materials (rocks and minerals) from which soil is made; examples in Malaysia include granite, limestone, and basalt.

Biota

The living plants and animals in soil whose activities and decomposition affect soil formation and organic matter accumulation.

Topography

The earth's surface contour which influences the rate of runoff, erosion, and water filtration during soil formation.

Soil Additions

The gain of materials from outside sources, such as precipitation adding water, dust adding minerals, or humans adding fertilizer.

Soil Losses

The removal of materials from the soil profile, such as water evaporation, surface erosion of particles, or leaching of nutrients.

Soil Translocations

The movement of organic or inorganic materials within the soil profile, either up or down between horizons.

Soil Transformations

The chemical or physical modification of soil constituents, such as dead leaves decomposing into humus or rock weathering into clay.

Soil Profile

A vertical section through the soil extending into the unweathered parent material, exposing all individual horizons.

Soil Horizon

A specific layer within a soil profile, occurring at different depths and possessing unique characteristics used to classify soil types.

O Horizon

The organic surface horizon consisting of un-decomposed or partially decomposed organic material (litter) and humus.

Humus

Rich organic material of plant and animal origin found in the O horizon that is in a stage of decomposition.

A Horizon (Topsoil)

The topmost mineral soil layer containing the most nutrients, the highest biological activity, and significant organic matter accumulation.

E Horizon (Elluvial)

A pale, nutrient-poor layer formed by leaching (eluviation), mainly consisting of silicate sand and silt.

B Horizon (Subsoil)

The layer of accumulation (illuviation) where materials such as clay, iron ($Fe$), and aluminum ($Al$) leached from upper layers collect.

C Horizon

The layer of partially weathered parent material and large rock lumps, containing very little organic material.

R Horizon (Bedrock)

The deepest horizon consisting of a continuous mass of unweathered bedrock.