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Transcript
Introduction to Soil Classification Debbie Surabian State Soil Scientist CT/RI USDA - NRCS Soil Taxonomy Soil Taxonomy was developed by the USDA Soil Conservation Service staff between 1951 and 1975. Soil Taxonomy Soil Taxonomy was designed to classify all the world's soils because expanding soil survey programs demanded more precise definitions of soil properties. – Organize knowledge of soils with similar properties – Facilitate communication among pedologists – Transfer information and technology Soil Taxonomy • Adopted in 1965 by Dr. Guy D. Smith, USDA • Official soil classification system of the United States • Has been recognition as a possible universal system for classifying soils. • To date, no system of classification has world wide acceptance – World Reference Base for Soil Resources (WRB) Criteria Used in Soil Taxonomy • Based on soil properties that can be observed and measured. • Chemical, physical, and biological properties such as moisture, temperature, texture, structure, pH, soil depth • Presence or absence of certain diagnostic horizons (surface and subsurface horizons) The Soils That We Classify The upper limit of soil is the boundary between soil and air [or] shallow water…[not] too deep (typically more than 2.5 meters) for the growth of rooted plants. The Soils That We Classify For purposes of classification, the lower boundary of soil is arbitrarily set at 200 centimeters. Hierarchical System of Soil Taxonomy Order (12) – Most general, based on soil forming processes. Sub-Orders (70) – Based on similarities in soil formation (moisture/temp/other). Great Groups (344) – Based on differences between soil horizons (diagnostic horizons). Sub-Groups (2,664) – Profile characteristics. Family (~11,332) – Based on properties that effect management (mineralogy, temperature) Series (~23,600) – Most specific, based on kind and arrangement of horizons. Phase – Field mapping units (stony, slope, other), not a category in soil taxonomy. Windsor Series Mixed, mesic Family Mixed Mineralogy Mean Annual Temp. 8 – 15c Typic Udipsamments Sub Order Sub Group Sandy Reflects Central Concept Great Group Humid Climate Order Entisol Twelve Soil Orders • • • • • • • • • • • • Entisol Inceptisol Andisols Spodosols Mollisols Alfisols Ultisols Oxisols Aridisols Vertisols Histosols Gelisols Soil Orders • • • • Highest level of classification Broadest group 12 orders Based on diagnostic horizons and climate Degree of weathering and soil development in the different soil orders Soil Taxonomy Global Distribution Entisols – 18% Inceptisols – 15% Mollisols – 7% Spodosols – 4% Histosols – 1% Entisols • • • • • Recent Very recent or young soils Little or no profile development No diagnostic subsurface horizons Form on • resistant parent materials, • mine spoils, • steep slopes, • floodplains Windsor Series Entisols • Simple soils to very productive alluvial soils • Pedogenically featureless (between “not soil” and horizonated soil) • Generally associated with human transported materials Is it Soil? No: active gravel pit No: pavement and buildings Yes: vegetated area, Fortress Series. Entisols – Six Suborders TYPIC UDIFLUVENTS TYPIC UDORTHENTS Hadley Series Manchester Series Inceptisols • inception (Latin, beginning) • Slightly more development than Entisols • Young soils but beginning of profile development is evident • May have a cambic horizon Gloucester Series Inceptisols – Seven Suborders AQUIC DYSTRUDEPTS TYPIC ENDOAQUEPTS Scitico Series Sutton Series Mollisols • • • • • mollis (Latin, soft) Very dark-colored soils Naturally fertile soils Typically form under grasslands Has a mollic epipedon: • Thick, humus-rich surface horizon • High % base saturation throughout profile Mollisols – Eight Suborders TYPIC ARGIUDOLL Sharpsburg Series TYPIC ENDOAQUOLLS Menlo Series Spodosols • From Greek spodos, “wood ash” • Acid soils with low fertility • Form in humid, cool climates and occur most often in conifer forests (New England, Mich., Canada) • Form in acid, coarse, quartz (sandy) bearing P.M. • Has a spodic horizon • Accumulations of organic matter and/or iron/aluminum oxides in the subsoil Spodosols – Five Suborders AQUODS AQUODS Histosols • histos “tissue” • Organic soils derived from hydrophytic plants • Low bulk density and very high water holding capacity Histosols – Five Suborders Alfisols • • • • pedalfer Naturally fertile soils High base saturation Clay-enriched subsoil horizon Aridisols • arid (Latin, dry) • Form in aridic soil moisture regimes (dry) • Low OM • Little leaching Ultisols • -ultimate (Latin, last) • Old, highly weathered, high degree of development • Low fertility Vertisols • invert (Latin, turn) • High clay soils (>30% sticky shrink-swell clays) • Deep cracks upon drying • Materials from soil surface fill cracks and become part of the subsurface when the cracks close (inverted soil) Andisols • ando (Japanese, black soil) • Form from P.M. of volcanic origin • Young soils • Can have unusually low bulk densities • High water holding capacity Oxisols • oxide (French, oxide) • Very highly weathered soils • Intense red or yellow color (high in oxidized iron) • Low native fertility Gelisols • gelid (Greek, cold) • Young soils with little profile development • High organic carbon content Series • Soil series predates Soil Taxonomy – used since 1899 • In 1975 there were 10,500 series in the U.S. and its territories; compared to about 23,600 series today • Lowest level of classification – can be subdivided into Phases • Typically name based on location where first identified Period of Soil Taxonomy Order Sub Order Great Group Sub Family Group Series Whitman Series Loamy, mixed, active, acid, mesic, shallow Family Particle Size Class Mixed Mineralogy Clay Activity Class Reaction Class Mean Annual Temp. 8-15c Soil Depth class (to Cd) Typic Sub Group Reflects Central Concept Humaquepts Sub Order Aquic Order Great Group Inceptisol Accumulation of Organic Matter in the Surface Deb’s Tips and Tricks to using Soil Taxonomy • Start from the beginning and work your way through the keys • If the criteria are not met, continue in order until they are met • Read and re-read each sentence • Use the Official Series Descriptions (OSDs) to learn how to key out pedons • Don’t assume the pit you dig will be a perfect match to any OSD pedon • Learn what you need to describe in the pit to classify your soil • Review Ch. 18 - nice explanation on designation for horizons and layers