Soils_1_2_3_4_2009

Soils_1_2_3_4_2009 - Geog 102 SOILS 1 I. SOILS DEFINITION...

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Geog 102 – SOILS 1 I. SOILS – DEFINITION AND PROPERTIES Old Version: Ch 18, p 592-600 New Version: Ch 18, p 595-602 A. DEFINITIONS Soil - Fig. 18.1 - uppermost layer of the earth’s crust or lithosphere - dynamic natural material made up of fine mineral and organic particles Pedology = soil science, study of soils B. SOIL COMPONENTS: how to identify soils Components Solid: mineral fraction and organic matter Pores: air and water 1. Mineral Fraction - physical framework of soils - fragments and mineral aggregates - classify minerals by the degree to which they have changed in physical or chemical composition over time: - primary minerals - secondary minerals - determines soil texture and structure Soil Texture = particle size distribution
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- size grades: gravel >2 mm in diameter sand 2 – 0.5 mm silt 0.5 – 0.002 mm clay < 0.002 –0.00001 mm colloids < 0.00001 mm - soil texture classes = combinations of sand, silt and clay - quantified by determining % sand-silt-clay in the soil - in the field, determined by feel, taste - in the lab, analyses and soil texture triangle Fig 18.4 For example, use the soil texture triangle to determine the texture class if…. a. 50% sand + 20% silt + 30% clay _________________________ b. 40% sand + 40% silt + 20% clay _______________________
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Soil Structure - Fig 18.5 - shape when grains aggregate, bound by colloids to form "peds" - 4 structures, determine water and air movement in soil: - granular/crumb - platy - prismatic - blocky 2. Organic Matter (OM) - partly decayed remains of plants and animals - humus = fine OM in soil = source of nutrients - soil colour = composition and chemistry - black/dark = - reds/yellows = - white/pale = - Munsell colour chart (175 colours) Fig 18.3
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3. Soil Air (gases) - important for plants/organisms and water movement - soil air relative to atmosphere: - depends on: - soil porosity - soil water 4. Soil Water - important for plants/organisms - held in soil pores, depending on a. b. Soil Solution = soil water + soluble constituents (ions) - critical for supplying nutrients to plants Ions Two sources in soil: - from physical and chemical weathering of soil minerals - released by organisms Two sets of ions important to plants: Bases = Cations - ions with positive charges - required plant nutrients - Ca 2+ , Mg 2+ , K + and Na + - measured as base saturation Acids - positive charges but NOT plant nutrients - H + and Al 3+ - measured as acidity on the pH scale
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Geog 102 – SOILS 2 SOILS - NUTRIENTS AND GEOCHEMICAL CYCLES Old Version: Ch 18, p 599-600 and Ch 19 634-7 New Version: Ch 18, p 600-602 and Ch 19 p 640-2 A. COLLOIDS, SOIL SOLUTION AND PLANT NUTRIENTS 1. Colloids = very fine inorganic (clay) and organic (humus) particles - large surface area to mass ratio - surface = negatively charged ions that attract and bond with ions in the soil 2. Soil Solution
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Soils_1_2_3_4_2009 - Geog 102 SOILS 1 I. SOILS DEFINITION...

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