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Transcript
Weathered Rocks from the lithosphere are the parent materials for soils Types of Parent Material • • • • • • Residual Colluvial Water Ice Wind Organic material Residual:Parent material in place The Castelleia series (CO) consists of well drained soils formed in thick noncalcareous, stony medium to moderately fine materials weathered locally from quartz, latite, or similar rocks. Nature of the parent material will greatly influence time it takes to make soil and the nature of the soil that is formed Colluvial debris: Rocks that have fallen down hills Arawak series, US Virgin Islands The Arawak series consists of shallow, well drained, slowly permeable soils on summits and side slopes of limestone hills and mountains. They formed in material weathered from soft limestone bedrock. 1 • Water:Alluvial deposits Sediment that is deposited by rivers • Water:Alluvial deposits Sediment that is deposited by rivers Water:Marine (sediments deposited by oceans) Forkwood soil, Wyoming The Forkwood series consists of very deep, well drained soils formed in slopewash alluvium derived from interbedded shale and argillaceous sandstone. Pamunkey soil, Virginia Soils of the Pamunkey series are very deep and well drained. They formed in Piedmont and Coastal Plain sediments. 2 Water:Lacustrine (materials deposited by lakes) Glacial till: Material transported by glacial ice Pleistocene Epoch 2 million years Glacial till: Material transported by glacial ice Glaciers - Loess • Summer – Melt water from glaciers would carry fine particles or sediment Eolian: Materials transported by wind Loess Loess - Illinois Peoria 25,000 - 12,000 • Winter – Water would dry out leaving dry sediment – Winter winds would transport the sediment Roxanna 60,000 - 26,000 3 Loess - China Loess - Washington Lanzhou - 440,000 sq km 50 - 300 meters deep From Gobi desert Paloose hills in eastern Washington Soil series Wallawalla Paloose Athena Eolian: Materials transported by wind Volcanic ash Organic:Wet areas where accumulation> decomposition Peat bogs (1)Parent materials + 4 other factors of soil formation • • • • Climate Topography Time Biota 4 We talked about rocks, rock weathering and parent materials How soil is formed Factors of soil formation Different scenarios For soil formation: Soil Science Taxonomy • Soil as a natural body • Each soil as a unique individual – Developed as a result of the 5 factors of soil formation Solum Regolith Soil formation is, simultaneously O Regolith- A weathered rock and soil that overlays bedrock Solum - portion of the regolith that shows the development of layers called soil horizons E B C • • • • • Breakdown of old Synthesis of new Losses Additions Translocations X Y Bedrock (1)Parent materials + 4 other factors of soil formation • • • • Climate Topography Time Biota Climate • Moisture – Quantity – Intensity – distribution • Temperature Can be interrelated and interact 5 Rainfall: Intensity and duration Role of water • Essential for chemical weathering • Transport materials through horizons • Determine type of plant cover Effective precipitation • Water has to go into the soil Temperature • Rate of biological activity Rate of chemical reactions – Infiltration - not overland flow – Rainfall exceeds evaporation Soil Development Time Line Topography Effect of Time Same parent material, same climate Organic Matter Accumulation Structural Development CaCO3 Accumulation Unweathered Loess CaSO4 Accumulation Time Location, location, location 6 Toposequence Excessively drained Well drained Poorly drained Biota - plants Very poorly drained Type of plant : Grass Soil Profile A - mollic horizon • Dense root system • Above ground foliage will die annually • Grows where moisture < trees • Thick A horizon Tree - deciduous • Leaves high in cations (Ca, Mg, Fe..) • Annual leaf fall • Well developed A horizon – Decomposed OM – High nutrients Deciduous • • • • Larger A horizon More cations Less acidic More clay translocation 7 Coniferous Acidic Tree - coniferous • Leaves low in cations • Little leaf fall Thin A • Thin A horizon E (eluviation) – Oi - slightly decomposed • E horizon – eluviation Animals • Pedoturbation – Animal burrows effectively mix soil from different horizons Animals • Humans – Agricultural practices – Accelerate soil loss – Accelerate soil formation Animals • Earthworms – Soil mixing – Soil structure – Soil aeration Start with a pile of rocks • Physical and chemical weathering – Breakdown particles – Change mineral structure 8 Plant starts growing • Organic matter is added to soil surface • Root exudates further break down minerals When a plant starts growing • Organic matter from plants is a nutrient source for other organisms First stage of soil formation • Increased organic matter in A horizon Next stage will involve development of a B horizon • Cations that have been solubilized by plant exudates, microbial activity,and acidification will start moving lower into the soil • Secondary clays have been formed in A and are also moving down the profile Beginning of a B horizon • Dark A horizon – Organic matter – Clays • Something below the A that looks different from the parent material • Parent material 9