Summary of Soils

Highlight Key Terms Key Concepts

Soil Formation Dynamic System Climate, biota, topography, parent material and time interact to form soil

Soil Profile Expression of soil forming factors varies with depth; thus soil characteristics change with depth

General Composition Porous Body Surface horizons have approximately equal volumes of solids and pores filled with water or air

Weathering Weatherable minerals decompose and more resistant minerals of clay size, clay minerals, form

Transported Materials Small particles may be transported by water, wind, ice or gravity to form new parent materials for soils
Physical Properties Soil Texture Surface area per unit volume of soil, and thus particle size, has profound influence on soil properties, especially reactivity

Soil Structure Arrangement of primary particles into secondary units has profound influence on porosity and balance between large and small pores
Soil Consistence Physical behavior of soils changes as moisture content changes

Soil Color Soil material that has a reddish hue is well drained; mottled and gray material are poorly aerated

Soil Chemical Properties Cation Exchange The ability of soil clays and organic matter to reversibly adsorb and exchange cations with soil solution
Soil pH A measure of the acidity or alkalinity of a soil; affects microorganisms, nutrient availability and plant growth

Soil Classification Soil Taxonomy Soils are classified based on presence or absence of diagnostic horizons and other differentiating characteristics

Soil Series The six tier system of classification uses words with Greek and Latin origins, except at the series level

Soil Survey Maps of soil occurrence on the landscape in relation to its classification make possible interpretations for various uses

Soil Environment Soil Water Held tightly in micropores. Matric potential, osmotic potential, wilting point. Soil biota must work to obtain water from soil

Soil Temperature Soil microbes are widely adapted for life at different temperatures. Thermal preferences for growth. Thermophile, mesophile cryophile.

Soil Aeration Waterlogging soil causes shift from aerobic (with O₂) to anaerobic (minus O₂) conditions. Efficiency of microbial processes is usually reduced; toxic substances may accumulate.

Soil Biological Properties Soil Biota Includes all life in the soil; macrofauna (worms, large insects, etc.)

Soil Microflora General term to collectively describe the populations of bacteria, fungi, protozoa, algae, etc.

Microbial Biomass The total mass of microbes in a soil. An important pool of nutrients with short turnover times. Driving force for most of the chemical reactions in soil.

Nutrient Cycling Nutrients such as carbon, nitrogen, phosphorus and sulfur are constantly recycled by soil microbes. Important for the continued functioning of earth’s ecosystems. Life itself must be recycled.
Bioremediation Controlled use of soil microbes for cleanup of oil spills, hazardous chemicals, etc. Relies on the great range of metabolic capacities of soil microbes.

Plant Essential Nutrients 16 Essential Elements All plants require these 16 chemical elements for proper growth and reproduction.

Nitrogen Cycle This dynamic system regulates the transformations and chemical forms of nitrogen in soils; related to plant growth and potential environmental pollution.

Soil Management Soil Testing The determination of the plant availability of essential nutrients in soils prevents over- and underapplication of fertilizers.

Erosion Loss of topsoil through the action of wind and water decreases productivity and increases costs from siltation, water purification, etc.

Tillage Cultivating soils aids in weed control, aeration, and water infiltration, but can make soils more susceptible to erosion. Conservation tillage reduces tillage, leaving crop residues on the soil surface to decrease erosion.

Soils and Societal Issues Population Growth Enlarging populations increase the pressure on soil resources for food production.

Urbanization Covering soils with highways, houses, and malls permanently removes land from agricultural production.

Landuse Planning This concept places greater emphasis on the public good as opposed to private property rights.

Critical Thinking Questions

Soil Section Beginning | Home

Highlight	Key Terms	Key Concepts
Soil Formation	Dynamic System	Climate, biota, topography, parent material and time interact to form soil
	Soil Profile	Expression of soil forming factors varies with depth; thus soil characteristics change with depth
General Composition	Porous Body	Surface horizons have approximately equal volumes of solids and pores filled with water or air
	Weathering	Weatherable minerals decompose and more resistant minerals of clay size, clay minerals, form
	Transported Materials	Small particles may be transported by water, wind, ice or gravity to form new parent materials for soils
Physical Properties	Soil Texture	Surface area per unit volume of soil, and thus particle size, has profound influence on soil properties, especially reactivity
	Soil Structure	Arrangement of primary particles into secondary units has profound influence on porosity and balance between large and small pores
	Soil Consistence	Physical behavior of soils changes as moisture content changes
	Soil Color	Soil material that has a reddish hue is well drained; mottled and gray material are poorly aerated
Soil Chemical Properties	Cation Exchange	The ability of soil clays and organic matter to reversibly adsorb and exchange cations with soil solution
	Soil pH	A measure of the acidity or alkalinity of a soil; affects microorganisms, nutrient availability and plant growth
Soil Classification	Soil Taxonomy	Soils are classified based on presence or absence of diagnostic horizons and other differentiating characteristics
	Soil Series	The six tier system of classification uses words with Greek and Latin origins, except at the series level
	Soil Survey	Maps of soil occurrence on the landscape in relation to its classification make possible interpretations for various uses
Soil Environment	Soil Water	Held tightly in micropores. Matric potential, osmotic potential, wilting point. Soil biota must work to obtain water from soil
	Soil Temperature	Soil microbes are widely adapted for life at different temperatures. Thermal preferences for growth. Thermophile, mesophile cryophile.
	Soil Aeration	Waterlogging soil causes shift from aerobic (with O₂) to anaerobic (minus O₂) conditions. Efficiency of microbial processes is usually reduced; toxic substances may accumulate.
Soil Biological Properties	Soil Biota	Includes all life in the soil; macrofauna (worms, large insects, etc.)
	Soil Microflora	General term to collectively describe the populations of bacteria, fungi, protozoa, algae, etc.
	Microbial Biomass	The total mass of microbes in a soil. An important pool of nutrients with short turnover times. Driving force for most of the chemical reactions in soil.
	Nutrient Cycling	Nutrients such as carbon, nitrogen, phosphorus and sulfur are constantly recycled by soil microbes. Important for the continued functioning of earth’s ecosystems. Life itself must be recycled.
	Bioremediation	Controlled use of soil microbes for cleanup of oil spills, hazardous chemicals, etc. Relies on the great range of metabolic capacities of soil microbes.
Plant Essential Nutrients	16 Essential Elements	All plants require these 16 chemical elements for proper growth and reproduction.
	Nitrogen Cycle	This dynamic system regulates the transformations and chemical forms of nitrogen in soils; related to plant growth and potential environmental pollution.
Soil Management	Soil Testing	The determination of the plant availability of essential nutrients in soils prevents over- and underapplication of fertilizers.
	Erosion	Loss of topsoil through the action of wind and water decreases productivity and increases costs from siltation, water purification, etc.
	Tillage	Cultivating soils aids in weed control, aeration, and water infiltration, but can make soils more susceptible to erosion. Conservation tillage reduces tillage, leaving crop residues on the soil surface to decrease erosion.
Soils and Societal Issues	Population Growth	Enlarging populations increase the pressure on soil resources for food production.
	Urbanization	Covering soils with highways, houses, and malls permanently removes land from agricultural production.
	Landuse Planning	This concept places greater emphasis on the public good as opposed to private property rights.