Soil classification and soil maps

  • View

  • Download

Embed Size (px)


Soil classification and soil maps. Why a classification system for soils? -mapping -taxation -inventory -management/use. Pedon – basic unit of soil classification. Classification system must be: 1. based on quantifiable characteristics of soils - PowerPoint PPT Presentation

Text of Soil classification and soil maps

  • Soil classification and soil maps

  • Why a classification system for soils?-mapping-taxation-inventory -management/use

  • Pedon basic unitof soil classification

  • Classification system must be:1. based on quantifiable characteristics of soils2. open-ended (we do not know about every soil)3. hierarchical (like biological systems)Also use new names (avoid old meanings and baggage)

  • The old (1938) system of soil classification

    -based on interpretation and assumed genesis-grouped soils based on climate/vegetation assemblages

  • Three ORDERS in old system

    Zonal or normal soils-climate inputs dominate a soils genesis-soil is in equilibrium with the climate/veg

    Intrazonal soils -salts, wetness or limestone bedrock overwhelm the soils genesis3. Azonal soils-too young, dry or sandy to have developed into Zonal soils

  • Zonal soils examples

    Podzols cool climates, coniferous forest

    Brunizems tallgrass prairies

    Sierozems desert soils

    Laterite soils red tropical soils

  • Intrazonal soils examples

    Rendzinas shallow to limestone bedrock

    Gley soils wet soils

    Peat soils

  • Azonal soils examples

    Dry, sandy soils

    Shallow-to-bedrock soils

    Alluvial soils (young parent materials)

  • The new system of SOIL TAXONOMY-adopted in 1975, revisions ever since

  • Order highest level (12)

    Suborder (>60)

    Great Group (about 300)

    Subgroup (about 1600)

    Family (>8000)

    Series (>14,000)

  • The 12 soil ordersGelisols cold soils, permafrost (-el)Histosols organic soils, usually Very PD (-ist)Spodosols podzolization, cool, moist forested areas (-od)Andisols volcanic ash parent materials (-and)Oxisols old, weathered soils of the humid tropics, oxide clays (-ox)Vertisols shrink-swell clays, wet-dry climate, deep cracks (-ert)Aridisols desert soils, some evidence of B horizon formation (-id)Ultisols 1:1 clays dominate, red, weathered soils but not like Oxisols (-ult)Mollisols thick, dark A horizon, grassland soils (-oll)Alfisols minimally weathered soils, lessivage, not highly acidic (-alf)Inceptisols weak B horizon development, some pedogenesis (-ept)Entisols most weakly developed soils, no diagnostic B horizon (-ent)

  • Fine, smectitic, mesic Xeric Argidurids Aridisol orderDurid suborderArgidurid Great GroupXeric Argidurid subgroupFamilySeries: Reno

  • Sandy, mixed, frigid Typic Haplorthods More about familiesTexture(Particle size family)MineralogySoil temperature regime (Table 7.13 in your book)Cation exchange class (sometimes) e.g., active, semiactive, superactiveDepth class (sometimes)Soil MOISTURE REGIME can be determined from the taxonomic name (weve done this already)

  • MASTCryic
  • FrigidMesicThermicHyperthemicCryic

  • FrigidMesicMesicMesic

  • Iso- minimal seasonal variation in soil temperature islands, and the tropics

  • Its usually possible to estimate the drainage class of a soil, knowing only its taxonomic subgroup. Heres how:Drainage class subgroup designation

    Well drained or drier ------- --------------Moderately well drained Aquic ----------------Somewhat poorly drained Aeric --------aqu-----Poorly drained ------- --------aqu-----Very poorly drained ------- -------------ist

  • More practice

    Fine-silty, siliceous, active, thermic Aeric Albaqualfs Coarse-loamy, mixed, superactive, calcareous, mesic Aquic Torriorthents Clayey, smectitic, shallow Typic Haplocryolls Coarse-loamy, mixed, active, mesic Aquic Fragiudepts Loamy-skeletal, mixed, superactive, thermic Cambidic Haplodurids Loamy, mixed, active, mesic Aquic Arenic Hapludults Drainage class subgroup designation

    Well drained or drier ------- --------------Moderately well drained Aquic ----------------Somewhat poorly drained Aeric --------aqu-----Poorly drained ------- --------aqu-----Very poorly drained ------- -------------ist

  • More about subgroups

    Three kinds:

    1. Central concept the TypicsTypic HaplorthodsTypic DystrudeptsTypic Eutrustox

  • More about subgroups

    Three kinds:

    Central conceptIntergrades trending toward another ORDERAlfic HaplorthodsSpodic DystrudeptsUltic Eutrustox

  • More about subgroups

    Three kinds:

    Central conceptIntergradesExtragrades with some other important or limiting attributeLamellic HaplorthodsLithic DystrudeptsAquic Eutrustox

  • Soil Taxonomy a quantitative system of soil classification, largely based on diagnostic horizonsDiagnostic horizons at the surface epipedons (all soils have one, and only one)Diagnostic subsurface horizons soils may have none, one, or several

  • Epipedons the major onesMollic mandatory for MollisolsCa++ ions common, base saturation >50%value
  • Epipedons the major onesAnthropic: resembles mollic, but can be dry high in phosphorous (due to long-term agriculture or human occupation)

  • Umbric: same as mollic, but base sat.
  • Epipedons the major onesHistic mandatory for Histosols water saturated for 30+ consecutive days (most years) organic materials dominate

  • Plaggen and Melanic minor ones, we wont discussEpipedons the major ones

  • Epipedons the major onesOchric: all others usually light colored, thin forested and dry soils

  • Entisols, by definition, lack a diagnostic B horizonDiagnostic subsurface horizons-can be E or B horizons

  • Diagnostic subsurface horizonsAlbic E horizons (must meet thickness and color requirements)

  • Diagnostic subsurface horizonsArgillic clay-enriched Bt horizons - illuvial silicate clays (NOT formed in place)indicates a stable surface, because illuviation is slow, and therefore it must exceed rate of argillan destruction if argillans are to be presentin sands, clay bridging is acceptableRequired for Alfisols, Ultisols

  • Diagnostic subsurface horizonsGlossic -degradation of an argillic (or kandic or natric) horizon -E/Bt or Bt/E -tongues of E material penetrating B material

  • Diagnostic subsurface horizonsNatric: same as argillic, but has either: (1) prisms/columns in upper part, or (2) high Na contentBn or Btn

  • The poop on Na+At low electrolyte concentrations, Na+ favors dispersion, just like other +1 cations(Na in upper profile can favor lessivage)

    At high electrolyte concentrations, as is typical of most desert and dryland soils, Na enhances flocculation.Btn becomes very clay-rich, and is virtually impermeable when wet. BtnBiscuit tops

  • Diagnostic subsurface horizonsKandic like argillic, but low CEC clays dominate has lots of kaolinite and many oxide claysBtKandiudultOnly in Ultisols

  • Illuvial clay ARGILLICNa-rich - NatricDegraded - GlossicOxide clays Kandic

  • Diagnostic subsurface horizonsSpodic - amorphous Al and humus, with or without Fe - sandy soils, little clay to inhibit podzolization - rapidly forming, under forest or heath veg.Bh, Bs, Bhs, Bsm, BhsmRequired for Spodosols

  • Diagnostic subsurface horizonsPlacic - thin pan, dark, cemented by Fe, Mn, and/or OC - 2-10 mm thick, brittleHas many similarities to Spodic horizon

  • Diagnostic subsurface horizonsOxic - mineral horizon in advanced stage of weathering- clay minerals are 1:1 or oxides- residual accumulation of Al, Ti, Fe and Mn- very old, stable surfaces- tropical/subtropical, wet/dry climatesBoRequired for Oxisols

  • Diagnostic subsurface horizonsCalcic - accumulation of secondary CaCO3If cemented PetrocalcicBk, BkmIfplugged - Bkk

  • Diagnostic subsurface horizonsGypsic - rich in secondary gypsum/sulfates - sea spray and gypsic parent materials are sources - difficult to differentiate from BkBy, BymIf cemented - petrogypsic

  • Diagnostic subsurface horizonsSalic - soluble salts (more soluble than gypsum)Bz

  • Sulfuric - pH < 3.5, yellow (jarosite) mottles - toxic to plants - in tidal marshesDiagnostic subsurface horizons

  • Diagnostic subsurface horizonsFragipan Btx, Bx, Ex

    Duripan silica cementation - Xeric soil moisture regimes - Bqm

  • Diagnostic subsurface horizonsWhen all else fails. Cambicweak "color" B horizon Bw horizon (some Bg horizons)must lack geologic structure or have soil structurenot sandy (Bw forms too quickly in sands)Having a Cambic horizon kicks the soil OUT of Entisols and (usually) into InceptisolsBw