NRES 201 Lecture 7 Outline of Last Lecture I. OrganismsII. TopographyIII. TimeIV. Weathering Outline of Current Lecture V. The soil in profileVI. Soil horizonsCurrent LectureThe Soil in Profile- What is the soil profile? A belowground vertical slice of the soil in place which includes a surface organic layer, if present (0 horizon), all mineral layers developed by soil forming processes (A, E, and B horizons), and underlying parent material (C horizon)- The importance of soil horizonation - o Horizons are a fundamental feature of most soils o Their presence reveals which factor dominated soil formationo Vegetation type was critical in Illinois Grass formed dark prairie soils and trees formed light forest soilso Rainfalls have a huge impact on soil development Poorly developed soils in arid regions Well developed soils in the tropics - Progressive nature of soil profile development o Stage 1 Mosses and lichens colonize bare rock O horizon appearso Stage 2 Grasses, shrubs, and stunted trees have rooted in a deepening layer of disintegrated rock and developing soil O horizon has increased A and C horizons have appeared o Stage 3 Forest trees now established The O horizon is very distinct The A horizon is thicker, darker, and more granular. 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. A bleached zone (E horizon) has lost Fe oxides and clay These materials have formed a B horizon The C horizons have thickened o Stage 4 The B horizon has gained more clay and developed a blocky structure. As weathering continues: - The soil becomes more acidic and less productive- Clay breaks down to Fe and Al oxides- The B horizon develops a red colorSoil Horizons- Distinguishing features - Color, Organic Matter Content, Texture, and Structure - Processes of Horizonation - Organic matter accumulation, loss (eluviation) through profile water movement, gain (illuviation) of material eluviated from other horizons, andtransformations in place. - Master soil horizons - o O = Organic Usually occur in forests but not in prairies. Absent from cultivated soils.o A = Mineral Topmost mineral horizons. Dark - colored by humus. o E = Mineral Light colored, common in forest soils but not prairie soilso B = Minerals Illuvial horizons characterized by accumulation of Clay/Fe/Al in humid regionso C = Mineral Unconsolidated material underlying the solum, may or may not be the soil's parent materialo R = Mineral Solum = O + A + E + B Only if highly decomposed Consolidated bedrock, no weathering- Transition horizons - Uniform mixture dominated by properties of one horizon - Subordinate distinctions - Specific horizon characteristics indicated by lowercase letters following the master horizon designation. o b = buried horizono g = strong gleying (mottling)o k = accumulation of carbonateso n = accumulation of sodiumo p = plowingo t = accumulation of clayo w = weakly developed B horizono x =
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