Transcript Soil Morphology and Classification
Soil Morphology and Classification
Purpose The Language of Soils Loamy, siliceous, hyperthermic grossarenic paleudult
Morphology and Classification of Soils Based on physical and chemical properties Color Texture Structure Density/Porosity Water Movement Reactivity of mineral and organic colloids Soil acidity and pH
Color Texture Dark/grayish-black color Orange vs. Gray colors Sandy vs. Clayey Structure Good vs. Poor Structure Density Water Reactivity Porosity, organic matter, compaction Pore sizes, porosity, water movement, saturation Cation exchange capacity Acidity Plant tolerances, buffering, base saturation All are used to classify soils
Soil Formation
Factors Affecting Soil Formation The 5 soil forming factors Climate Organisms/Vegetation Parent material Topography Time
Climate Temperature and Precipitation Rates of chemical, physical, biological processes Cold dry climates – weak to modest profile development Warm, humid climates – strong, deep profile development
Organisms/Vegetation O.M. accumulation Profile mixing Nutrient cycling Soil structure Soil solution (% B.S.)
Parent Material Affects texture, vegetation, nutrients clay mineralogy, CEC Deposition Colluvial (gravity) Alluvial (streams) Marine (oceans) Lacustrine (lakes) Glacial (ice) Eolian (wind) silt and clay
Topography Configuration of land surface – elevation, slope, depressions Hastens or delays climatic forces.
Impacts depth of profile development.
Slope Aspect Water Erosion Vegetation
Time Duration of weathering and all other factors Additions losses translocations transformations
McCarty Hall
Stable, older sediments
Hawthorne Formation (geologic Clay) Limestone
E
Shands
Younger sediments
Soil Horizons: first step in classification
Soil Horizon designations
O horizon A horizon Organic matter E horizon Sandy B horizon Clays/iron Master Horizons O organic A topsoil, O.M., cycling E elluvial B developed/accumulation C parent material R bedrock C horizon Parent
Master Horizons
Enough information?
O horizon A horizon E horizon (Elluvial) C horizon B horizon (Illuvial)
R horizon
B horizon
Subordinate Distinctions
Subordinate Distinctions b – buried horizon c – concretions d – root restrictive
g – gleying h – illuvial organic matter
k – carbonates m – cementation
o - oxic p – plowing/disturbance
q – secondary silica r – soft bedrock (saprolite) s – illuvial sesquioxides and O.M.
t – clay accumulation
v – plinthite
w – development of color/structure
x - fragipan
Subordinate Distinctions
g – gleying h – illuvial organic matter p – plowing/disturbance t – clay accumulation w – development of color/structure o – oxic
Subordinate Distinction
(g = gleying)
• • • •
Oxygen deprived or reduced state due to water saturation.
Reduction of iron (Fe III to Fe II) low chroma Often used with B master horizon (Bg horizon), also E and C horizon.
Fe 3+ oxidized material Fe 2+ gleyed material oxidized
Subordinate Distinction
h = organic accumulation
• Accumulation of • h = “humic” illuvial organic matter-metal complexes • Coatings on sand and discrete particles • value and chroma approximately 3 or less • Used with the B master horizon (e.g. Bh horizon) * Bh horizon “spodic horizon”
Subordinate Distinction
p = plowed
Disturbed surface horizon (cultivation, pasture, forestry) Used with the A master horizon (e.g. Ap horizon) Ap horizon
Subordinate Distinction
t = clay accumulation
Translocation of clay or formed in place Coatings or discrete Used with the B master horizon (e.g. Bt) If reduced, can be used with the g sub horizon (Btg)
Subordinate Distinction
w = color or structure
Non-illuvial development of color or structure “w” can = “weak” Commonly used with the B master horizon (e.g. Bw) Bw
Subordinate Distinction o = oxic horizon Low activity clays Few weatherable materials Little rock structure Fe and Al oxides
Subordinate Distinctions
g – gleying h – illuvial organic matter p – plowing/disturbance t – clay accumulation w – development of color/structure o – oxic
Subordinate Distinctions and Organic Matter
Subordinate Distinction a, e, i Denotes the degree of organic matter decomposition in the O horizon .
Oa – highly decomposed (sapric) Oe – moderately decomposed (hemic) Oi – slightly decomposed (fibric) Sapric –most decomposed, low plant fiber, low water content Hemic – intermediate decompostion Fibric – least decomposed, recognizable fibers
Summary
Master: O, A, E, B, C, R Subordinate symbols: g, h, p, t, w and a,e,i Examples: Oa, Oe, Oi Bt Bg Btg Bw Ap
Other Designations
Vertical Subdivisions
Characterized by similar master and/or subordinate properties separated by “degree”.
Bt horizons Bt1 Bt2 Bt3
Transitional Horizons
Transitional layers between master horizons.
Dominant character A E E B B E Subordinate Character
Synthesis Ap AE E Bh Bt Btg1 Btg2
Soil Taxonomy
Soil Classification/Taxonomy
Hierarchical Based on soil profile characteristics and the concept of soils as a natural body.
Observable properties: color, texture, structure, pH, O.M… Soil Profile Genesis 1883 V.V. Dukachaev: climate, vegetation, soil 1927 C.F. Marbut (USDA) applied to U.S. (1965)
Soil Classification/Taxonomy
USDA classification system Soil Survey Staff 1965
Soil Taxonomy
published 1975 • Adamsville : Hyperthermic, uncoated Aquic Quartzipsamment
Soil Taxonomy Hierarchy
Order Suborder Great group Sub group Family Series 12 63 250 1400 8000 19,000 Kingdom Phylum Class Order Family Genus Species
Units for Soil Classification
Pedon – smallest three-dimensional unit that displays the full range of properties characteristic of a given soil. (1-10 m 2 of area) - the fundamental unit of soil classification Polypedon – group of closely associated pedons in the field Soil Series – class of soils world-wide which share a common suite of soil profile properties
Soil Sampling Units
Malabar Series
Diagnostic Horizons for Classification
Surface Subsurface
Diagnostic Surface Horizons
Epipedons Mollic Umbric Ochric Histic Melanic Plaggen Anthropic
Diagnostic Surface Horizons
Melanic X Plaggen Histic
Mollic
X Umbric X Ochric X Anthropic X = Florida
Mollic Epipedon
Thickness Color Organic Carbon Base Saturation Structure > 18-25 cm value < 3.5 moist chroma < 3.5 moist > 0.6 % > 50 % strongly developed Organic carbon = organic matter x 0.57
Umbric Epipedon
Meets all criteria of the Mollic epipedon, except base saturation < 50% Chemically different than Mollic
Ochric Epipedon
Too: thin light low in O.M
Mollic Umbric Ochric = pale Extremely common
Histic Epipedon
Organic horizon Formed in wet areas Black to dark brown Low bulk density 20-30 cm thick Organic = > 20% - 35% O.M.
( water saturation, clay content)
Melanic Epipedon
Similar in properties to Mollic Formed in volcanic ash Lightweight, Fluffy
Anthropic Horizon
• Resembles mollic (color, o.m.) • Use by humans • Shells and bones • Water from humans
Plaggen Epipedon
Produced by long-term (100s yrs.) manuring Old, human-made surface horizon Absent in U.S.
> 50 cm thick
Diagnostic Surface Horizons
Epipedons Mollic Umbric Ochric Histic Melanic Plaggen Anthropic Very common “specialized” Human-derived
Organic Matter Accumulation
O.M. accumulation Parent material Vegetation established time Histic Mollic, Umbric ochric t max = 3000 yrs
Diagnostic Sub-surface Horizons
Diagnostic Subsurface Horizons
Formation Translocation Transformation Clays Organic Matter Oxides
Subsurface Horizons
Organic Matter Dark colors Metals (Fe, Al) Clays smectites Kaolinite Formation Translocation Transformation Oxides Iron Aluminum Also: salts, carbonates, sulfides
Diagnostic Subsurface Horizons
Albic Argillic Spodic Oxic Kandic Cambic Sombric sulfuric Natric Agric Calcic Gypsic Salic Duripan Fragipan Placic Sub-Horizon Designations
Diagnostic Subsurface Horizons
Albic (white) Horizon Light-colored (Value > 6 moist ) Elluvial (E master horizon*) Low in clay, Fe and Al oxides Generally sandy textured Low chemical reactivity (low CEC) Typically overlies Bh or Bt horizons *not all E horizons are albic horizons albic
Diagnostic Subsurface Horizons
Argillic Horizon Illuvial accumulation of silicate clays Illuvial based on overlying horizon Clay bridges Clay coatings
Diagnostic Subsurface Horizons
Argillic Horizon High Activity of Clays Kandic Horizon Low Necessary Illuviation of clay Not Necessary
Diagnostic Subsurface Horizons
Spodic Horizon • Illuvial accumulation of organic matter and aluminum (+/- iron) • Dark colored (value, chroma < 3) • Low base saturation (acidic) • Formed under humid acid conditions Spodic
Elluviation and Illuviation
Elluviation (E horizon and A horizons) A E Bh Organic matter Bh horizon Spodic horizon Clays Bt horizon Argillic horizon A E Bt
Diagnostic Subsurface Horizons
Oxic horizon • Highly weathered (high temperatures, high rainfall) - High in Fe, Al oxides activity - High in low-activity clays (kaolinite < smectite < vermiculite)
Diagnostic Horizons
Epipedons Mollic Umbric Ochric Histic Melanic Plaggen Anthropic Subsurface Albic Kandic Argillic Spodic Oxic
Soil Taxonomy
Diagnostic Epipedons Diagnostic Subsurface horizons Moisture Regimes Temperature Regimes