NRES 201 Lecture 8 Outline of Last Lecture I The soil in profile II Soil horizons Outline of Current Lecture III Rationale for classification IV Soil taxonomy Current Lecture Rationale 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 regimes Diagnostic surface horizons Mollic epipedon o Formed under grass o Dark colored thick o High organic matter o High in basic cations Umbric epipedon o Like a mollic epipedon but more acidic These 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 epipedon o Mineral horizon that does not qualify as a mollic or umbric epipedon Melanic epipedon o Not found in Illinois can be found in Philippines etc o Developed from volcanic ash o Light in weight and fluffy Histic epipedon o Formed in wet areas o Thick organic horizon overlying a mineral soil Diagnostic subsurface horizons Albic Horizon o 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 clay o High pH o Poor physical properties due to soil dispersion o Occurs in arid and semiarid regions Cambic Horizon o Illuvial horizon o May show carbonate depletion Kandic Horizon o Illuvial horizon with accumulation of low activity of clay o Occurs below an abrupt boundary Oxic Horizon o Illuvial horizon with extensive accumulation of low activity clay o Found in humid tropical and subtropical regions Spodic Horizon o Found highly leached forest soils of cool humid climates Calcic Horizon o Found in arid and semiarid regions
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