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Chapter 7

Chapter 7.docx

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Monika Havelka

Chapter 7- Soil Resources Central Case: Mer Bleue Bog • A 35km^2 protected weland • Peat soils formed over 8000 years; up to 6m thick • Carbon balance in peat:  Primary production stores carbon  Decomposition releases carbon • Interdisciplinary research project studying the influence of climate on carbon balance (viceversa) Soil is a Complex Material • Soil consists of mineral matter, organic matter, water, air, and other gases  Dead and living microorganisms and decaying material  Bacteria, algae, earthworms, insects, mammals, etc  Can support plant growth Soil formation starts with bedrock • Parent material = base geologic material of soil • Bedrock= continuous mass of solid rock (the Earth’s crust) • When the parent material is exposed to the effects of the atmosphere, hydrosphere, biosphere • Parent can be lava or volcanic ash; rock or sediment deposited by glaciers; wind-blown dunes – any type of bedrock • Weathering = processes that break down rocks o Regolith sediment = broken up rock o Lunar regolith- no soil on the moon, it’s lunar sediments but no organic component to it so it’s not truly soil • Physical (mechanical)= no chemical changes in the parent material • Chemical= substances chemically interact with parent material • Biological = organisms break down parent material Soil Formation is very slow • Factors that affect soil formation:  Parent material composition (mineral content)  Climate (temperature, precipitation- contributes to erosion of rock)  Topography (steepness of slope- cannot retain soil very well)  Vegetation (root activity, protective cover)  Biological activity (soil microbes and fauna; decomposition and accumulation of organic matter) • Can take 10,000 years or more to form a well developed soil profile  Soil profile consists of horizons o Soil profile= the cross-section of soil as a whole o Horizon= layer of soil o Layers differ in colour, texture, nutrient content/chemical composition o Leaching: dissolved particles move down through horizons Humus • Stable, decomposed organic matter • Contributes significantly to soil structure; influences water retention, nutrient content, cation exchange capacity Types of Soil • As much as 10,000 types in Canada alone • Differ in colour, texture, acidity, etc • Have big influence of what kind of plants can go there Soil Colour • Colour indicates composition  Black or dark brown= organic matter  Pale gray or white= leaching (downward movement of organic material)  Red= iron Soil Texture: determine by the size of particles • Proportion of sand(0.05 to 2mm), silt (0.003 to 0.05mm) , and clay (>0.002mm) • Particle sizes and pore sizes: influences how air and water pass through the soil • Loam= even mixture of sand-silt-slay; best for plant growth Soil Structure • How the sand, silt, and clay particles are held together • Organic matter interact with mineral particles to form aggregates of various shapes and sizes • Affect pore size and distribution; affects the ability to drain and provide adequate aeration • Good soil structure (tilth) will allow plants to establish extensive root systems Plough Pan • Repeated tilling compacts soil: resists water infiltration and root penetration Soil Ph • Soil pH (acidity) influences the soil’s ability to support plant growth • Affects bioavailability of nutrients • Affects toxicity of some compounds (e.g. Al^3+) • Nutrient Availability and pH Soils provide plants with: • A medium for roots • Water • Nutrients through adsorption and ion exchange • Nutrients through bacterial processes Ion exchange is vital for plant growth • Charges particles move between soil, water, and plants by ion exchange • Charged humus and clay particles in soil hold positively-charged cations of Ca, Mg, K (adsorption) Cation Exchange Capacity (CEC) • Ability to hold cations; protects from downward leaching • Greatest in fine soils • Increases nutrient availa
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