Soil Science Midterm

soil

1) a dynamic natural body composed of mineral and organic solids, gases, liquids, and living organisms which can serve as a medium for plant growth 2) the collection of natural bodies occupying parts of the Earth's surface that is capable of supporting plant growth and that has properties resulting from the integrated affects of climate and living organisms acting upon parent material, as conditioned by topography, over periods of time

pedology

The science/study of the formation, morphology, and classification of soil bodies as landscape components

edaphology

The science that deals with the influence of soils on living things, particularly plants, including human use of land for plant growth

humus

the more or less stable fraction of the soil organic matter remaining after the major portions of added plant and animal residues have decomposed (dark in color)

regolith

the unconsolidated mantle of weathered rock and soil material on the Earth's surface; loose earth materials above solid rock (some engineers equate this term with soil) (on Earth, regolith includes soil)

horizon

a layer of soil, approximately parallel to the soil surface, differing in properties and characteristics from adjacent layers below/above it

genetic horizon

soil layers differing from adjacent layers in some observable property as a result of soil-forming (pedogenic) processes, as opposed to sedimentation or other geologic processes.

diagnostic horizon

horizons having specific soil characteristics that are indicative of certain classes of soils. The properties of these horizons must be measurable with some kind of further testing besides just looking at it.

epipedon

a diagnostic surface horizon that includes the upper part of the soil that is darkened by organic matter, or the upper eluvial horizons, or both (diagnostic horizons occurring AT soil surface) ex: mollic

diagnostic subsurface horizon

diagnostic horizons occurring BELOW the soil surface, ex: argillic

soil profile

a vertical section of the soil through all horizons and extending into the parent material

parent material

The unconsolidated and more or less chemically weathered mineral or organic matter from which the solum of soils is developed by pedogenic processes (the original material that soil develops from)

solum

The upper and most weathered part of the soil profile that inludes A and B horizons; set of altered layers/related soil horizons above the parent material that share the same cycle of pedogenic processes

A horizon

The surface horizon of a mineral soil having maximum organic matter accumulation, maximum biological activity, and/or eluviation of materials such as iron and aluminum oxides and silicate clays (below O horizon, above all other horizons)

B horizon

zone of accumulation; a soil horizon usually underneath A or E horizon that is characterized by one or more of the following: 1) concentration of soluble salts, silicate clays, iron and aluminum oxides, and humus, alone or in combination 2) a blocky or prismatic structure 3) coatings of iron and aluminum oxides that give darker, stronger, or redder color

E horizon

characterized by maximum eluviation (washing out) of silicate clays and iron/aluminum oxides; commonly occurs above B horizon and below A and usually much lighter in color

illuviation

the process of deposition of soil material removed from one horizon to another (material being deposited down to a lower horizon)

eluviation

the removal of soil material in suspension or in solution from a layer/layers of soil; loss of material referred to as leaching, dominant in an E horizon

alluvial

soil deposited by flowing water (rivers or streams)

C horizon

A mineral horizon, generally beneath the solum (A & B), relatively unaffected by biological activity and pedogenesis and is lacking properties diagnostic of an A or B horizon. May or may not be like the material from which A and B have formed; partially altered parent material

topsoil

1) the layer of soil moved in cultivation 2) presumably fertile soil material used to top-dress roadbanks, gardens, lawns

subsoil

the part of soil below the plow layer or surface soil

sand

a soil textural class; largest soil separate consisting of particles between 2.00 and 0.05 mm in diameter

silt

a soil textural class; medium soil separate consisting of particles between 0.05 and 0.002 mm in equivalent diameter

clay

a soil textural class; smallest soil separate consisting of particles less than 0.002 mm in diameter

soil texture

the relative proportions of the various soil separates in a soil (sand, silt, clay)

soil separate

one of the individual-sized groups of mineral soil particles (sand, silt, or clay)

primary mineral

A mineral that has not been altered chemically since deposition and crystallization from molten lava

secondary mineral

a mineral resulting from the decomposition of a primary mineral or from the reprecipitation of the products of decomposition of a primary mineral

soil structure

the combination/arrangement of primary soil particles into secondary particles, units, or peds. These secondary units are characterized and classified on the basis of size, shape, and degree of distinctness into classes, types, and grades, respectively

pedon

the smallest sampling unit that displays the full range of properties characteristic of a soil; the smallest volume that can be called 'a soil'

soil organic matter

the organic fraction of soil that includes plant and animal residues at various stages of decomposition, cells and tissues or soil organisms, and substances synthesized by the soil population

what are the four major components of soil

air, water, mineral matter, organic matter

what is CLORPT

the five factors of soil formation: climate, organisms (biotic activity), relief (topography), parent materials, and time

what are the five factors of soil formation

CL (climate) O (organisms) R (relief) P (parent material) T (time)

what are the processes by which soil forms

destructive (weathering of rock and decay or organic residues) and synthetic (formation of new materials like clays and organic compounds)

describe the difference between THE soil and A soil

THE soil = all soil on Earth's crust, A soil = an individual body of soil from the soil

weathering

the breakdown of rocks and minerals at or near Earth surface into products more in equilibrium with conditions found in the environment

what are the types of weathering

chemical, physical, biological

chemical weathering

alteration of chemical and mineralogical composition of materials (ex hydration, hydrolysis, oxidation, dissolution, carbonation)

physical weathering

breakdown by mechanical methods and decreasing particle size with no change in chemical composition (ex abrasion, crystallization, thermal isolation, wetting and drying, pressure release, frost wedging)

exfoliation

peeling away layers of a rock from the surface inward, usually as the result of expansion and contraction that accompany changes in temperature

hydrolysis

a reaction with water that splits the water molecule into H+ and OH- ions

hydration

chemical union between an ion or compound and one or more water molecules, the reaction being stimulated by the attraction of the ion or compound for either the hydrogen or the unshared electrons of the oxygen in the water

oxidation

the loss of electrons by a substance; therefore, a gain in positive valence charge and in sone cases combination with oxygen gas

solution

liquid consisting of ions dissociated from the surfaces of soil particles and of other soluble materials

what are types of chemical weathering reactions?

hydrolysis, hydration, solution, and oxidation-reduction

residual parent material

parent material weathered in place; developed in place from weathering of the underlying rock

types of parent material

residual, colluvial (coarse and stony, physical weathering dominant), alluvial (deposited by water), marine, lacustrine (deposited in lake water and later exposed by lowering water level or elevated land), glacial

floodplain

the land bordering a stream, built up of sediments from overflow of the stream and subject to inundation when the stream is at flood stage

terrace

a level, narrow plain bordering a river/lake/sea

drift

material of any kind deposited by geological processes in one place after having been removed from another

till (both noun and verb)

1) unstratified glacial drift deposited directly by the ice and consisting of clay, sand, gravel, and boulders 2) to plow and prepare for seeding

outwash

deposit of coarse materials left by streams of meltwater from glaciers

moraine

an accumulation of drift, with an initial topographic expression of its own, built within a glaciated region chiefly by the direct action of glacial ice

peat

unconsolidated soil material consisting largely of undecomposed/slightly decomposed organic matter accumulated under conditions of excessive moisture

loess

material transported and deposited by wind and consisting of predominantly silt-sized particles

soil-forming processes

additions (input of materials to developing soil profile from outside), losses (leaching/other removal forms), transformations (soil constituents modified or destroyed and others synthesized from the precursor materials), translocations (movement of inorganic/organic materials laterally within a horizon or vertically from one horizon up/down to another.

R horizon

unweathered parent material; consolidated rock

what is a ped

a unit of soil structure such as an aggregate, crumb, prism, block, or granule, formed by natural processes (clump)

what is bulk density

the mass of dry soil per unit of bulk volume, including air space

what are the causes of soil color

organic matter content, water content, presence and oxidation states of iron and manganese oxides

what is the relationship between particle size and specific surface area?

smaller = more surface area (sand has least, clay has most); more SSA causes more capillarity and therefore more water retention

polypedon

two or more contiguous pedons, all of which are within the defined limits of a single soil series or soil individual

soil series

a subdivision of a family in soil taxonomy consisting of soils that are similar in all major profile characteristics

what are the soil moisture regimes

aridic, xeric, ustic, udic, aquic

what are the soil temperature regimes

hyperthermic, thermic, mesic, frigid, cryic, pergelic

what are the hierarchical categories of soil taxonomy?

order, suborder, great group, subgroup, family, series

what is the most specific category of soil taxonomy?

series

mineralization

the conversion of an element from an organic form to an inorganic state as a result of microbial decomposition

immobilization

the conversion of an element from the inorganic to the organic form in microbial tissues or in plant tissues, thus rendering the element not readily available to other organisms or to plants

volatilization

the conversion of a liquid chemical into vapor that escapes into the ambient air

ammonification

the biochemical process where ammoniacal nitrogen is released from nitrogen-containing organic compounds