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21 Cards in this Set

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What is the definition of soil?

"Dynamic natural body, composed of mineral and organic material and living forms in which plant grow"


or


"A collection of natural bodies occupying part of the earth's surface that supports plants and that have properties due to the effects of climate and living matter acting on parent material, conditioned by relief over a period of time"

Explain how soil is a dynamic system.

As new mineral and organic matter is incorporated old material is broken down, altered, moved, re-deposited or lost from the profile.

What is the sequence and what are the events of soil formation?

-Weathering or rock (parent material)


-Accumulation and mixing of organic matter.


-In situ formation of weathering products.


-Transport, accumulation and loss of material.

What helps develop the distinct soil horizons?

The movement and accumulation of mineral and organic matter down the soil profile.

What are the different soil horizons?

O - Plant and animal residues (litter) and decomposing organic matter. Of - fibrous peat and Op - amorphous organic matter mixed by cultivation.




A - mixture of mineral and humified organic matter. Ah - uncultivated and Ap - cultivated.




E - eluvial - zone where soil is depleted of insoluble and soluble material by evulation and leaching e.g., organic matter, silicate clays, Fe and Al oxides, Ca2+ and Fe2+.




B - illuviation - zone of accumulation. Bh - accumulation of translocated humus, Bt - accumulation of translocated silicate clays, Bs - enriched with Fe and Al oxides: orange to red colour and Bg - evidence of gleying: reduction of iron.




C - Parent material.

What effects soil variation?

Climate - rain and temperature.


Biology - plants, animals and microbes.


Parent material - weathering or rocks and minerals.


Topography - drainage.


Time - effects all of the above.


Management - cultivation.



How does physical weathering influence soil properties?

Two types thermal and mechanical both lead to the break down of rocks;




Thermal - mineral expansion or ex-foliation (onion skin weathering).


Mechanical - frost shattering, swelling and shrinking and biological weathering.




Influenced by particle size and state of consolidation.

How does physical weathering influence soil properties?

Hydrolysis - H+OH.


Carbonation - H2CO3.


Hydration - H20.


Dissolution - H20.


Oxidation and reduction - O2.




All alter the chemical composition of rocks and therefore lead to break down of rocks.




Influenced by mineralogy and chemical compositor.

What are the different sizes of particles?

Sand - 0.02 - 2.00 mm.


Silt - 0.02 - 0.002mm.


Clay - <0.002mm

What are the main types of parent material?

Sedentary (solid, pre-glacial geology) - igneous, metamorphic or sedimentary.


Transport (drift) - sedimentary, geologically recent (Quaternary) and predominant soil and landscape forming materials in the UK.

What are the general parent materials in the UK?

-In the upland zones of the UK, parent materials are mostly pre-glacial and include all three rock types.


-In the lowlands the predominant soil forming materials are quaternary sediments of glacial aeolian, alluvial, colluvial or biogenic origin which were laid down at various stages (during the last million years) in the evolution of the present landscape.

What varies the physical and chemical properties of drift in lowland UK?

-The mineralogy of the rocks from which the drift was derived.


-The extent of weathering prior to deposition.


-The transport processes that deposited the drift.

What transport materials deposit drift materials?

Ice - glacial.


Water - glacial and alluvial.


Wind - aolian.


Gravity - colluvial.

What types of glacial drift are there?

Glacial till - deposited by ice sheets during the cold stages.


Fluvio - glacial deposits - deposited by the melt waters during the warm (temperate) stages.

What is aeolian drift?

-Glacial origin.


-Not common in the UK but important in the USA.


-Often mixed with glacial drift.

What is colluvial drift?

-Accumulated material (mostly <10,000 years old) on the sides and bases of slopes and valleys.


-Coarse and stoney.


-Agriculturally unimportant.

What is alluvial drift?

-Recently (<10,000 years ago) deposited by flooding streams and rivers that run their current course.


-Particle sizes range from large stones to fine clays.


-Particles are sorted into different sizes during the flood, with larger material being deposited near the river channel and finer materials further away.

What climate factors affect soil formation in the UK?

Temperature - function of latitude and altitude, mild winters in the UK lowlands and cool summers in the UK especially with increasing altitude.


Precipitation - annual rainfall ranges from 550 mm in lowland East and South to 5000 mm in mountains in the west.

What climate factors affect soil formation?

The shape of the land affects the evolution of the soil by causing differences in climate, ground surface stability and moisture regimes (hydrological sequences i.e. undulating landscapes usually on permeable drift materials commonly have freely draining soils in the upper slope and hilltop positions and progressively less well drained soils in lower positions where the water table approaches the surface, combined with changes in parent material over short distances).

What are Catenas?

-A sequence of soil types down a hill slope.


-Common in the UK especially on nearly uniform, drift parent materials.


-Topographically related patterns of soil changes.

What influences vegetation and management?

-Acidity inputs.


-Organic matter accumulation.


-Soil surface stability.


-Soil moisture.