NRES 201 Lecture 8 Outline of Last Lecture I. The soil in profileII. Soil horizonsOutline of Current Lecture III. Rationale for classificationIV. Soil taxonomy Current LectureRationale for classification:Soil heterogeneity - - The five soil forming factors interact to produce nearly endless variety in soils. Soil formation never stops so the variety expands over time. Soils as individuals - - Soils characterize as pedons (the smallest 3 dimensional unit that has all the properties of a particular soil.)- A polypedon is a group of similar pedons and constitutes a soil individual - A soil series consists of all soil individuals whose properties fall within a certain range. Reasons for soil classification - - To organize knowledge of soils, to better understand relationships among soils, to provide information pertinent to similar soils elsewhere in the world. Soil taxonomy:Bases of classification - - The surface part of the pedon (epipedon) - organic matter, texture, color, structure, cation composition- The subsurface part of the pedon - drainage, color, accumulation of clay/Fe/Al- Climate - moisture and temperature regimesDiagnostic surface horizons- Mollic epipedon o Formed under grasso Dark colored, thicko High organic mattero High in basic cations- Umbric epipedono Like a mollic epipedon but more acidicThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Forms in areas with higher rainfall- Ochric epipedono Mineral horizon that does not qualify as a mollic or umbric epipedon- Melanic epipedono Not found in Illinois - can be found in Philippines, etco Developed from volcanic asho Light in weight and fluffy- Histic epipedono Formed in wet areaso Thick organic horizon overlying a mineral soilDiagnostic subsurface horizons- Albic Horizono Light colored eluvial horizon depleted of clay o Low in fertility - Argillic Horizon o Illuvial horizon with clay accumulation o Clay accumulates on ped surfaces, between sand grains, as pore linings- Natric Horizon o Illuvial horizon with accumulation of clayo High pHo Poor physical properties due to soil dispersion o Occurs in arid and semiarid regions - Cambic Horizono Illuvial horizono May show carbonate depletion - Kandic Horizon o Illuvial horizon with accumulation of low - activity of clayo Occurs below an abrupt boundary- Oxic Horizono Illuvial horizon with extensive accumulation of low - activity clayo Found in humid tropical and subtropical regions- Spodic Horizono Found highly leached forest soils of cool, humid climates - Calcic Horizon o Found in arid and semiarid
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