Introductory Soils Lab 1B Soil Profiles NRES 201 Page 1 of 7 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 silt -------------- Si silty clay --------------SiC loamy sand ---- LS silt loam ------- SiL sandy clay loam -----SCL sandy loam ---- SL clay loam ------ CL sandy clay ------------SC loam ------------ L clay ------------ C 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. The purpose of using horizon designations is to reflect the describer’s interpretations of the genetic relationships between the horizons in a soil. 2. 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, CIntroductory Soils Lab 1B Soil Profiles NRES 201 Page 2 of 7 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 BIntroductory Soils Lab 1B Soil Profiles NRES 201 Page 3 of 7 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