Soil Systems and Society Flashcards

Vocabulary flashcards covering fundamental soil concepts, soil horizons, soil properties, system flows, and specific soil types.

Soil

A dynamic ecosystem and complex mixture of four basic components: mineral particles from weathered parent rock, organic matter from organism decay, air, and water.

Humus

A dark brown or black loose, crumbly substance lying beneath leaf litter formed by the partial decay of dead plant material that influences nutrient retention, water retention, and soil aeration.

O Horizon

The uppermost organic layer of the soil profile consisting of leaf litter and decaying organic material (humus).

A Horizon (Topsoil)

The soil layer directly beneath the uppermost organic humus layer, rich in organic matter, oxygen, and microorganisms; known as the mixed layer where most root growth occurs.

B Horizon (Subsoil)

The soil horizon beneath topsoil characterized by the accumulation of deposited minerals and metal salts leached from upper horizons.

C Horizon (Parent Rock)

The soil horizon consisting of partly weathered parent rock material lying directly above the unweathered bedrock.

R Horizon (Bedrock)

The layer consisting of continuous, unweathered parent rock at the base of the soil profile.

Soil Profile

A vertical cross-section of soil showing its distinctive horizontal layers (horizons) from the surface down to the parent rock.

Soil Texture

The physical classification of mineral soil based on the relative proportions of sand, silt, clay, and organic components.

Sand

Soil mineral particles derived from quartz ranging in size from $2.00 - 0.05\,mm$, providing high drainage and aeration but low water retention and low cation exchange capacity.

Clay

Complex silicate mineral particles smaller than $0.002\,mm$ with high water retention, poor drainage, and high cation exchange capacity.

Loam

A soil type containing a balanced combination of sand, silt, and clay, offering optimal water retention, nutrient availability, and drainage for agricultural productivity.

Soil Texture Triangle

A triangular diagram used to determine soil texture classification based on the relative percentages of sand, silt, and clay.

Leaching

The transfer or output process by which water moving downward through soil horizons dissolves and carries away soluble plant nutrients and minerals.

Salinisation

A soil transformation process involving the accumulation of soluble salts in soil due to high rates of evaporation, often exacerbated by irrigation.

Cation Exchange Capacity (CEC)

The measure of a soil's ability to hold and exchange positively charged mineral nutrients, such as $Ca^{2+}$, $Mg^{2+}$, and $K^{+}$, for plant uptake.

Brown Earths

Soils typical of temperate deciduous forests characterized by merged horizon boundaries due to biological mixing by organisms like earthworms, moderate leaching, and dispersed iron and aluminum oxides.

Oxisols

Highly weathered, acidic soils found in tropical and subtropical rainforests characterized by intense chemical weathering, heavy nutrient leaching, and a reddish/yellowish oxic horizon rich in iron oxides.

Loss on Ignition (LOI)

A laboratory method used to measure percentage organic matter in soil by burning off organic material from a dry sample and calculating the resulting change in mass.

Methane Clathrates

Geological structures underlying permafrost containing trapped methane that can break down and release greenhouse gases when rising temperatures cross a critical tipping point.