Introductory Soils Lab 1B Soil Profiles NRES 201 LABORATORY 1B DESCRIBING SOIL PROFILES Soil cores can be collected in the field with hand or power coring devices that retrieve undisturbed samples A variety of information can be determined by a visual inspection of fresh and fixed soil cores in the laboratory The profile is described by identifying the individual horizons that are present their depth color structure and texture Other information about the soil which may also be determined from a visual inspection includes parent material natural drainage class and soil classification 1B 1 SOIL HORIZONS 1 Depth cm The mineral surface is assigned a depth of zero Record depth to the center of the boundary separating each horizon from the one below i e 0 15 cm 15 30 cm etc Horizons thinner than 7 5 cm are not ordinarily described with the notable exceptions of E Bh and Bs horizons 2 Texture Standard name and abbreviations are used to describe the texture of each horizon sand S loamy sand LS sandy loam SL loam L silt Si silt loam SiL clay loam CL clay C silty clay SiC sandy clay loam SCL sandy clay SC silty clay loam SiCL 3 Color Use the Munsell soil color book to determine the moist color of each horizon Surface horizons should be crushed color subsurface should be broken peds Record the color using the hue value chroma notation a Mottling Mottling is the presence of more than one color due to impeded drainage b Coats Ped coats can be of contrasting color due to translocated clay carbonates or organic matter 4 Horizon name See list and definitions of the master horizons and subordinate distinctions Horizon Designations 1 2 The purpose of using horizon designations is to reflect the describer s interpretations of the genetic relationships between the horizons in a soil Capital letters lowercase letters and Arabic numerals are used to form horizon designators a Capital letters are used to designate master horizons b Lowercase letters are used as suffixes to indicate specific characteristics of the master horizon c Arabic numerals are used as suffixes to indicate vertical subdivisions within a horizon and as prefixes to indicate lithologic discontinuities Previously Arabic numerals were used as suffixes to indicate a kind of O A or B horizon and to indicate vertical subdivisions of a horizon and Roman numerals were used as prefixes to indicate discontinuities The first parent material is assumed and therefore 1 is not used e g loess over till A Bt1 Bt2 2Bt3 2BC 2C d A prime is used too indicate repeated designations e g A E Bt E Bx BC C Page 1 of 7 Introductory Soils Lab 1B Soil Profiles NRES 201 Common Master Horizons Old Current Situation O O Organic horizon A A Surface mineral horizon topsoil A1 A First surface mineral horizon topsoil A2 E Eluvial horizon below A horizon A3 AB or EB Transitional horizon between A and B E Bt lamellae Found in sands B B Illuvial horizon has subordinate distinction B1 BA or BE Transitional horizon between B and A B3 BC or CB Transitional horizon between B and C C C Unweathered parent material massive calcareous R R Bedrock Common subordinate distinctions within master horizons Old Current Situation a highly decomposed organic matter used with O b b buried soil horizon used with O A or B d dense layer physical root restriction used with B or C e intermediately decomposed organic matter used with O g g strong gleying used with E B or C h h illuvial accumulation of organic matter used with B i slightly decomposed organic matter used with O ca k accumulation of carbonates used with B m m strong cementation used with Bk na n accumulation of sodium used with B p p plowing or other disturbance used with A r r weathered or soft bedrock used with C ss presence of slickensides used with B C t t accumulation of silicate clay used with B w weak development of color or structure used with B x x fragipan used with B Page 2 of 7 Introductory Soils Lab 1B Soil Profiles NRES 201 1B 2 PARENT MATERIALS Parent Material refers to the geologic material s from which the soil profile has developed More than one type of parent material is possible This is shown with an arabic number in front of the horizon symbol i e 2Bt etc 1 Recent Alluvium Material that has been transported by streams sediments and deposited on present day flood plains or stream terraces typically stratified 2 Outwash Old alluvium Material deposited by glacial meltwaters typically stratified and coarser than recent alluvium Found on high stream terraces and on outwash plains 3 Glacial Till Non stratified unsorted glacial material deposited by glaciers in ground lateral and terminal moraines very common in Illinois 4 Lacustrine Sediments Relatively fine SiCL SiC C well sorted stratified materials deposited in fresh water lakes often associated with glaciation 5 Residuum Unconsolidated bedrock weathered in place no transporting agent involved found typically in unglaciated regions 6 Colluvium Material deposited on footslopes primarily by the action of gravity may include local alluvium deposited by overland flow 7 Eolian Sand Sand accumulated through the action of wind into dunes 8 Loess Wind deposited silt sized material very common in Illinois and excellent parent material for agriculture because of high moisture holding capacity and natural fertility 9 Coastal Plain Sediments Lacustrine or outwash like material deposited along coast into oceans and seas later exposed after relative seal level drops 1B 3 SOIL DRAINAGE CLASSES The natural drainage class and aeration status of a soil can be determined from soil colors and color patterns The red color of soils is generally related to the presence of unhydrated iron III oxides Fe2O3 hematite coating soil particles although manganese dioxide and partially hydrated iron III oxides may also contribute red colors Red colors may also be inherited from parent materials or developed by the oxidation of iron minerals by soil weathering processes Red colors are stable only in soils that are well aerated The yellow color of soils is largely due to the presence of hydrated iron III oxides Fe2O3 3H2O limonite Soils with yellow colors tend to occupy moister landscape positions than associated red soils this results in the hydration of the iron III oxides Brown colors are associated with well drained soils and are due to coatings of goethite FeO OH on soil particles Grey and whitish colors of soils are related to uncoated silt and clay grains as the reduction associated