Chapter 18 Outline

Chapter 18 Outline - Chapter 18: The Geography of Soils...

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Chapter 18: The Geography of Soils Introduction Soil - natural material made of fine particles in which plants grow; contains mineral fragments, organic matter; soil system incl human interaxns, supports human/animal/plant life; contains info about past; soils can’t reproduce/be re-created; soil science - interdisciplinary- pedology concerns: Origin, classification, distribution, description of soil- about soil as natural body; edaphology - re: soil’s practical uses- medium for sustaining higher plants; stresses plant growth, fertility, diffs in soil productivity; agricultural extension service can provide specific info/detailed analysis of local soils Soil Characteristics Soil Profiles Soil profile must be studied surface plant roots/where regolith/bedrock encountered; such a profile- pedon - is hexagonal column 1–10 m 2 in top surface area; at its dies, the various lyrs of soil profile visible in cross section, labeled w/letters (see pg. 578 ); pedon basic sampling unit used in soil surveys Many pedons together in an area=> polypedon , w/distinct characteristics diff’iating it fr surrounding polypedons; =soil indv, comprising identifiable series of soils in a n area; min dimension ~1 m 2 ; is basic mapping unit used in preparing local soil maps Soil Horizons Soil horizon - each distinct layer exposed in a pedon; ~parallele to pedon’s surface, has chars diff fr other horizons; boundary btwn diff ones ~clear on basis of color, texture, structure, consistence, porosity, presence/absence of certain minerals, moisture, chem. processes Soil horizons building blocks of soil classification; top of soil profile- O (organic) horizon : organic composition, fr plant/animal litter deposited on surface, turned humus - mix of decomposed, synthesized organic materials, usu dark in color; microorgms work on this, doing part of: Humification (humus-making) process; O horiz 20-30%+ organic matter=>impt ability to retain water, nutrients/complement to clay minerals; bottom of soil profile- R (rock) horizon - loose material or consolidated bedrock; A, E, B, C horizs in descending order mark diff mineral strata btwn O, R: A horizon - humus, clay particles impt- provide chem. links btwn soil nutrients, plants; richer in orgnic content, darker than lower horizs; where human disruption, eg plowing occurs; grades into E horizon- coarse sand, silt, resistant minerals; fr here, silicate clays + Aluminum, Fe oxides leached: (Removed by water), carried to lower horizs as H 2 O percolates thru soil; this removal of fine particles/ minerals by water, leaving behind sand/silt= eluviation ; rate of eluv incr w/tht of precip; B horizon accumulates clays, Al, Fe; dominated by illuviation - depositional process (eluv= erosional)… May have red/yellowish hues due to illuviated presence of minerals/organic oxides; some B materials maybe there due to weathering processes rather than translocation (migration); humid trops, these lyrs
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This note was uploaded on 06/24/2008 for the course GEOG 1 taught by Professor Okin during the Fall '06 term at UCLA.

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Chapter 18 Outline - Chapter 18: The Geography of Soils...

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