NRES 201 Lectures 4 6 Fall 2014 Soil Formation NRES 201 Soil Formation 1 Soil Formation Today s lecture topics Nature of soil genesis Rocks the basic ingredient of soils Parent materials Residuum Colluvium Alluvium Marine sediments 2 1 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Nature of soil genesis How soils form Soils form naturally at the Earth s surface At the interface between geological materials and the atmosphere Soils form gradually over time Through the weathering of parent material by climate and organisms interacting with topography The parent material comes from rocks Source Nardi 2007 3 The four soil forming processes Transformations Chemical or physical changes in soil constituents Destruction or synthesis Translocations Movement of materials within or between horizons Water is the transporting agent Source Brady and Weil 2010 4 2 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Additions From external sources Examples include Fallen plant leaves Sloughed off roots Losses To the external environment Examples include Leaching to groundwater Erosion Source Brady and Weil 2010 5 Rocks the basic ingredient of soils Igneous rocks Originate from molten magma below the Earth s crust Form by the cooling of volcanic lava Often contain interlocking mineral grains Common examples Granite Basalt Diorite Source http www huffingtonpost com 6 3 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Sedimentary rocks Formed from igneous rocks Sediments settle under water and recement The dominant type of rock Common examples Sandstone Sandstone Limestone Shale Source http geology com 7 Metamorphic rocks Formed from igneous or sedimentary rocks under extreme temperature and pressure Endless variety Common examples Marble Marble Quartzite Slate Source http geology com 8 4 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Summary table Source Singer and Munns 1987 9 Mineralogical composition Minerals occur in rocks as solid crystalline substances Primary minerals in igneous rocks Secondary minerals in sedimentary and metamorphic rocks Formed by the weathering of primary minerals Major mineral groups Silicates Aluminosilicates Metal oxides hydroxides Carbonates Sulfides Sulfates 10 5 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Elemental composition Oxygen and silicon are the most common elements Because silicate minerals make up more than 90 of the Earth s crust 11 Parent materials Formed by weathering Rocks disintegrated by Temperature changes Note the Erosive action of water change after this ice and wind marble In 1944 Plants and animals statue had Rocks decomposed by weathered Hydrolysis for 58 Hydration years Carbonation Oxidation In 2002 Dissolution Source http www whatischemistry unina it 12 6 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Potential for transport Inorganic parent materials do not necessarily form in place They may be transported from one site and deposited at another Possible transporting agents Gravity Flowing water Glaciers Wind Transport often leads to sorting by size 13 Importance to soil properties Texture Coarse texture from sandstone Fine texture from shale Affects drainage and aeration Soil reaction Alkalinity from limestone Acidity from sulfide rich shale Affects natural vegetation and chemical weathering 14 7 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Mineral composition Affects clay mineralogy and land use Also affects soil fertility Soils are more fertile when there is a high content of minerals that supply Calcium Ca Magnesium Mg Potassium K Over eons of time soil fertility declines as these minerals are depleted by weathering Native vegetation shifts toward species having low fertility requirements 15 Residuum Derived from rock that weathers in place No transporting agent Often the parent material for older soils Source http www nrcs usda gov 16 8 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Prominent in mountainous and upland regions of the USA the Great Plains and the Piedmont Residuum prominent in green shaded regions Source Brady and Weil 2008 17 Colluvium Material moved by gravity and deposited at the base of steep talus slopes Unstable prone to landslides Usually very coarse textured and well drained Highly variable in composition Source http soilweb landfood ubc ca 18 9 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Colluvial soils are poorly developed and often lack horizons Source http www pinterest com 19 Alluvium Material deposited by flowing water Deposition can occur in Floodplains Which become terraces if the stream changes grade Coarser sediments settle near the stream channel Source Brady and Weil 2010 20 10 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Floodplain soils are Nearly level Highly fertile Missouri River floodplain eastern Missouri Source http webspace ship edum 21 Floodplain soils are Nearly level Highly fertile Often stratified Source http jscnwy wordpress com iceland 22 11 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Deposition can occur in Alluvial fans Formed by a sudden descent in stream flow that deposits sediment at the base of a slope Sorted by size Coarser particles at the top Finer particles at the bottom Alluvial soils are Often highly fertile Prone to flooding Kenai Peninsula Alaska Source http epod usra edu 23 Deposition can occur in Deltas Formed at the mouth of some rivers as sediments deposit from slow moving water An extension of the floodplain Delta soils are Fine textured Highly fertile Poorly drained Nile River and Delta Egypt Source http en wikipedia org 24 12 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Deposition can occur in Freshwater lakes Analogous to delta formation Known as lacustrine deposits Size sorted with Sand and gravel at the entrance point Silt and clay in most of the lake Lacustrine soils are Layered Fine textured Poorly drained Lacustrine deposit in an old lakebed Source http soilweb landfood ubc ca 25 Marine sediments Gradual accumulation of sediments carried by stream flow into oceans estuaries and gulfs A coastal plain builds up over time Acidification occurs during soil formation Coastal plain soils Vary widely in texture and productivity Are more level near the coast than inland Sandy soil in the Atlantic Coastal Plain Source http verdant123 com 26 13 NRES 201 Lectures 4 6 Fall 2014 Soil Formation Soil Formation Today s lecture topics Nature of soil genesis Rocks the basic ingredient of soils Parent materials Residuum Colluvium Alluvium Marine sediments 27 Today s key