Chapter 3 Learning Objectives Chapter 3 • Describe the current USDA soil classification system • List the six categories of classification in Soil Soil Taxonomy Taxonomy • Describe the major characteristics, the general degree of weathering and soil development, and the worldwide distribution and uses of the 12 soil orders • List key features of a particular soil and its environment given the soil name (e.g., Hapludalf) Diagnostic Subsurface Horizons Diagnostic Subsurface Horizons • 18 of them – Albic: light-colored elluvial horizon (leached) – Cambic: weakly developed horizon, some color • Six we will focus on (and the assoc. genetic change label): – Spodic: illuvial horizon with accumulations of O.M. – Argillic: subsurface accumulations of silicate clays – Albic (E) -Argg(illic (Bt) – CliCalcic: accumu ltilation o f car bona tes, o ften as – Cambic (Bw) - Fragic (Bx) white, chalk-like nodules – Spodic (Bhs) - Calcic (Bk) – Fragipan: cemented, dense, brittle pan Light colored horizon Albic Argillic Weakly developed horizon Cambic No significant accumulation silicate clays Unweathered Accumulation of Acid weathering, material organic matter Fe, Al oxides Spodic Calcic Fragipan Modified from full version of Figure 3.3 in textbook (page 62). 1 Levels of Description Levels of Description • Order Most general • Order – One name, all end in “-sol” There are 12. Differentiated by presence or absence of • Suborder diagnostic horizons or features that reflect • Great group soil-forming processes. EXAMPLE: ENTISOL • Subgroup • Suborder • Family • Great group • Subgroup •Series •Family Most specific •Series Levels of Description Levels of Description • Order – One name, all end in “-sol” There are 12 . • Order – One name, all end in “-sol” There are 12 . • Suborder – One name, last 2-3 letters • Suborder –properties (e.g., climate info) AND order indicates the soil order. Tells something • Great group – 3 pieces of info. Last 2-3 letters about properties important to genesis and tell the order, includes suborder info, and plant growth (e.g., climate info) Example: adds info about the horizons (e.g., sandy, Aquent clay ey, hard… ) EampleExample: Psammaquent • Great group • Subgroup • Subgroup •Family •Family •Series •Series Levels of Description Levels of Description • Order – One name, all end in “-sol” There are 12 . • Order – One name, all end in “-sol” There are 12 . • Suborder –properties (e.g., climate info) AND which • Suborder – Tells something about properties (e.g., Order climate) • Great group – 3 parts, adds info about the horizons • Great group – 3 parts, adds info about the horizons • Subgroup – TWO words. All info from above plus whether it is “typical” or shares • Subgroup – TWO words. properties with another soil type. Example: • Family – name includes about 5-6 words! Mollic Psammaquent Adds physical and chemical properties that •Family affect growth of plants •Series •Series 2 Soil Taxonomy Levels of Description • Order – One name, all end in “-sol” There are 12 . Order • Suborder – Tells something about properties (e.g., climate) • Great group – 3 parts, adds info about the horizons • Subgroup – TWO words. •Family – name includes about 5-6 words! • Series – Often referred to by a single name that doesn’t tell you anything unless you already know it well. 12 Soil Orders Fig 3.5 3 Soil Orders Soil Order “Formative Characteristics, Entisols element” location, etc. Entisol -ent Absence of distinct pedogenic horizons; climate & PM key Inceptisol -ept Gelisol -el Histosol -ist Andisol -and Aridisol -id Entisols Soil Orders • Sandy, young soils Soil “Formativ Characteristics, location, etc. Order e • Plainfield loamy sand: element” Typic Udipsamment Entisol -ent Absence of distinct pedogenic horizons; climate & PM key Inceptisol -ept Weak development, nothing exciting. There is a “B” horizon Gelisol -el Histosol -ist Andisol -and Aridisol -id Inceptisol: few horizons, inception Soil Orders of B (Bw) Soil “Form. el” Characteristics, location, etc. Order Entisol -ent Absence of pedogenic horizons Inceptisol -ept Weak development Gelisol -el Permafrost, freeze-thaw fea tures (13% o f so ils worldwide!) Lithic Eutrudept - northern Histosol -ist Michigan Andisol -and Aridisol -id 4 Gelisols: permafrost Gelisols • cryoturbation Soil Orders Gelisols Soil “Form el” Characteristics, location, etc. Order Entisol -ent Absence of distinct pedogenic horizons Inceptisol -ept Weak development GlilGelisol -el PftfPermafrost, freeze-thaw Histosol -ist Very high OM in upper 80 cm (peats), wet Andisol -and Aridisol -id Histosols: organic soils Histosols • Wetland delineation 5 Soil Orders Andisols Soil “Form el” Characteristics, location, etc. Order Entisol -ent Absence of horizons Inceptisol -ept Weak development Gelisol -el Permafrost, freeze-thaw Histosol -ist Very high OM, wet Andisol -and Volcanic soils, Al-humus complexes, mild temp, fairly moist Aridisol -id Soil Orders Andisols Soil Ending Characteristics, etc. Order Entisol -ent Absence of distinct pedogenic horizons Inceptisol -ept Weak development Gelisol -el Permafrost, freeze-thaw Histosol -ist Very high OM, wet Andisol -and Volcanic soils Aridisol -id No avail. H2O when plants growing – the largest group of soils on Earth! Aridisols: dry soils Aridisols • 12% globally •9% US 6 Soil Orders Vertisol: swelling and cracking Soil Order “Formative Characteristics, clays element” location, etc. Vertisol -ert Swelling clays, high BS, dry-wet Mollisol -oll Ultisol -ult Alfisol -alf Spodosol -od Oxisol -ox Vertisols Soil Orders Vertisols Soil Ending Characteristics, location, etc. Order Vertisol -ert Swelling clays, high BS Mollisol -oll Dark, thick epipedon, grasslands, some dry period, high BS Ultisol -ult Alfisol -alf Spodosol -od Oxisol -ox 7 Mollisol: dark, grassland, high base sat. • Loess: silt Mollisols • 22% of US • Very productive Plate 8 Mollisols -- a Typic Hapludoll from central Iowa. Mollic epipedon to 1.8 ft. Scale in feet. Soil Orders Ultisols Soil Ending Characteristics, etc. Order Vertisol -ert Swelling clays, high BS Mollisol -oll Dark, thick, grasslands Ultisol -ult Wet subtroppp,gyical or tropical, highly acidic, high in clay, Fe and Al oxides, productive if add fertilizers Alfisol -alf Spodosol -od Oxisol -ox Soil Orders Ultisols: Bt w/ low bases Soil Ending Characteristics, etc. Order • More Vertisol -ert Swelling clays, high BS leached than Mollisol -oll Dark, thick, grasslands Alfisols Ultisol -ult subtropp,ical, acidic, ,g high in clay, y,, Fe, Al • Less fertile Alfisol -alf Moist, forested, mildly acidic, translocation of clays, moderate-high BS Spodosol -od Oxisol -ox 8 Alifsols Alfisols: Bt, ochric epipedon Soil Orders Soil Endin Characteristics, etc. Spodosols Order g Vertisol -ert Swelling clays, high BS Mollisol -oll Dark, thick, grasslands Ultisol -ult Moist & warm, acidic, high in clay, oxides Alfisol -alf Moist, forested, clays Spodosol -od Translocation of humus and Al, Fe, cool, wet, sandy, coniferous forest Oxisol -ox Spodosol: Bs, Bh or Bhs, albic Spodosols horizon • Northern Wis – Orthods: typical of central concept of Spodosols 9 Soil Orders Soil Ending Characteristics, etc. Oxisols Order Vertisol -ert Swelling clays, high BS Mollisol -oll Dark, thick, grasslands Ultisol -ult Moist & warm, acidic . Alfisol -alf Moist, forested, clays Spodosol -od cool, wet, sandy, acidic . Oxisol -ox Extreme weathering, tropical forest, Fe, Al oxides, old, stable PM Oxisols • Tropical • Highly weathered Development and soil orders Development of the soil orders Bk ice Bo 10 The SUPER SIMPLIFIED guide to soil orders The SUPER SIMPLIFIED guide (cont.) 1. If no subsurface horizons Æ Entisol 6. If on volcanic material Æ Andisol 2. If aridic moisture regime and NOT and 7. If TONS of clay, with shrink-swell features Entisol Æ Aridisol (“slickensides,” large cracks when dry) Æ 3. If mollic epipedon Æ Mollisol Vertisols 4. If histic epppipedon Æ Histosol 8. If spodic horizon (Bh, Bs) Æ Spodosols 5. If permafrost Æ Gelisol 9. If oxic horizon (Bo) Æ Oxisols The SUPER SIMPLIFIED guide (cont.) 10.If umbric epipedon (low BS), argillic horizon, subtropical location Æ Ultisol 11.If ochric epipedon (sometimes umbric), argillic horizon, often an albic horizon, and a cool, moist climate Æ Alfisol 12.If oc hr ic ep ipe don an d NOT an En tiso l or Aridisol, often a cambic horizon Æ Inceptisol Soil Taxonomy Suborder 11 Suborders • Often described based on climatic information • Name of the suborder tells what order the soil belongs to PLUS one other feature of the soil (usually climate, except for Aridisols…) Soil Moisture Regimes Soil Temperature Regimes o COLD • Aquic – saturated for extended periods WET • Pergelic - < 0 C • Udic – not dry for more than 90 days • Cryic – 0-8, cold summer • Frigid – 0-8, warm summer • Ustic – dry 90-180 days •Mesic –8-15 • Xeric – dry summer, moist winter • Thermic – 15-22 • Hyperthermic - >22 • Aridic – moist <90 days HOT • Torric (not a real moisture regime but used in • Iso-(frigid, mesic, thermic, hyperthermic): small difference between summer and winter names like one. dry + hot ) DRY Suborders Suborders (cont.) • Often described based on climatic information Also differentiated based on key features – Aqu - wet •Fluv: fluvial, from a river – Ud - moist –Ust -dry • Psamm: sandy – Xer – moist winter, dry summer • Alb: albic horizon (()E) – leached – Torr – hot and dry • Arg: argillic horizon (Bt) – clayey –Cry –very cold – Hist – histic epipedon • Orth: “other” or “true to the definition” • Example: Aqualf (note capitalization) 12 Examples