Download ENV Ch 13 Soils

ENVR SCI Nov. 2012
Ch 13. Soil and its Uses.
Geologic Processes
Earth’s Composition – Core (Fe, Ni) Solid Inner
Mantle (Silicate ) Solid inner, Plastic-like outer.
Crust – Fragmented, solid (plates): Continental 4.5 BY,
light color, relatively light weight. Max. thickness 70 Km; Oceanic Crust 200 MY,
dark color, heavy weight, Max thickness 10 Km.
Plate Tectonics – 12 major fragments (Plates) many small pieces, in motion
(Tectonics).
Plate boundaries- Divergent (Pull apart) , example Mid Ocean Ridge ; On land
examples East Africa ,and Baja California.
Convergent (Collision) example on land – Ural Mts, Himalayas, Where Ocean crust
collides with Continental crust – Subduction occurs, example Trenches in the
western Pacific.
Transform boundaries. Where plates move horizontal relative to each other.
Example San Francisco.
Plate movement results from the transfer of asthenosphere matter by convection
cells, and gravity pull.
Soils.
Loose (unconsolidated) material on the surface of the land.
Importance of the soil is due to its influence on (a) Crop yield. (b) what crops are
grown and (c) the method of farming practiced.
Soil type is a function of (a) the parent rock. (b) the climatic and (c) the
topography.
Soil formation can be (a) Physical- the fragmentation of rock by any means. (b)
Chemical – (1) Hydrolysis resulting from water infiltrating into the rock and
subsequently causing its disintegration. (2) Oxidation from oxygen entering into
the rock pores leading to its disintegration. (3) Dissolution caused by water
dissolving the solid rock. (c) Biological – when an organism ingests a rock and
emits finer grain sizes or when it extracts calcium carbonate or silica from the
surrounding waters and produces solid rock material.
Soil Properties –
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Texture – grain size (Pebbles/sand/silt/clay)
Structure – ability to clump worst case; best texture soil is loam.
Composition – the chemical material present in the rock.
Porosity - pore space in the soil.
Biotic Content – organic material in the soil.
Soil Profile is observed in the color changes with depth. The Zone of leaching is
the uppermost horizon, otherwise called the A Horizon; The Zone of
Accumulation is the B Zone; The deeper Zone or C Horizon is the weathered zone.
Below the C horizon is the Parent Rock. Additionally, there is an Organic zone (O
Zone) on the ground surface. An E Horizon is a thin brightly colored E Zone at the
base of the A horizon.
Soil Types of particular interest are Desert soil called Pedocal; and Rain forest soil
is a Pedalfer. Prairie soil is particularly fertile because of its content of organic
matter, and good porosity.
Soil Erosion is the wearing away and removal of the soil by Ice or Water or Wind.
As a consequence of erosion, soil fertility is reduced, air and water pollution is
increased, dredging of waterways becomes critical for barge and ship
transportation in land, and fish habitats are destroyed.
Soil Conservation is maintained by several methods, but the most common is by
(a) enhancement of organic matter in the soil. (b) No Till farming. (c) Efficient
pest’s management. (d) Prevention of Compaction. (e) Crop diversity and or
rotation. (f) Maintain ground cover.
Presently, US soils are used 20% crops, and 24% pasture.
Europe uses 30% for crops and 17% for pasture.
Africa has 6% in cropland and 3% in pasture.
The Methods of Farming
The major influencing factors are : Climate, Plot size, soil texture, Topography,
Drainage, and Fertility.
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Contour farming (Tilling direction)
Strip farming (alternating ridges tilled)
Terracing (does not accommodate heavy machinery)
Use of wind breaks and sodded waterways.
Conservation Practices:
 Mulch tillage
 Strip Tillage
 No Till
Conventional Farming generally follows the procedure of Plow, Disc and Harrow –
three times before planting.
Benefits to conservation practices are: Less erosion less fuel use; less soil
compaction; more free time;
Drawbacks to conservation practices: lower production; more fertilizer use; more
pesticide use;
US Federal land use classification: 8 groups
Grazing; lumber harvesting; wild life protection; watershed protection; Urban;
industrial; crop land and Recreation.