Nancy Van Wagoner, Acadia University Soils Nancy A. Van Wagoner Acadia University

Nancy Van Wagoner, Acadia University What is soil? l Mineral Matter l Organic Material –litter (undecomposed) –humus (decomposed) u light, spongy u absorbs water –water –air

Nancy Van Wagoner, Acadia University Soil Formation l Weathering –converts bedrock to regolith u regolith = layer of rock and mineral fragments produced by weathering l interaction of weathered mineral matter with organic matter produces soil

Nancy Van Wagoner, Acadia University Composition of soil in good condition for plant growth l overhead

Nancy Van Wagoner, Acadia University Soil Profile (fig )

Nancy Van Wagoner, Acadia University O Layer l organic layer l mostly litter and humus l little mineral matter

Nancy Van Wagoner, Acadia University A Horizon l Zone of Leaching –receives rain first, so soluble minerals are leached out l contains most organic material (humus) l zone of intense biological activity –roots –burrowing animals –worms –micro-organisms l mostly clays

Nancy Van Wagoner, Acadia University B Horizon l Zone of accumulation (subsoil) –precipitation of ions dissolved from Horizon A –little organic material

Nancy Van Wagoner, Acadia University C Horizon l partially altered bedrock l very little organic matter l merges at the base with bedrock

Nancy Van Wagoner, Acadia University Soil Forming Factors l Parent material or bedrock type l Time l Development of organic material l Slope angle and aspect l Climate

Nancy Van Wagoner, Acadia University Parent Material or Bedrock Type l Influences –rate or weathering or soil formation u mineralogy (mineral stability) of bedrock u consolidation of bedrock –chemical composition of soil u parent material provides nutrients to the soil –texture of the soil u granite produces sandy soil u basalt produces clayey soil

Nancy Van Wagoner, Acadia University Time l It takes a long time to form soil l Generally, the longer the soils has been forming the thicker and more distinctly layered it is l Soil is always being eroded from the surface by –natural processes –anthropogenic processes (plowing and tilling) l At the same time weathering deepens the soil l If the rate of erosion exceeds the rate of soil generation the soil is lost and it can take thousands of years to form again.

Nancy Van Wagoner, Acadia University Development of Organic Material l Organic material in soil promotes chemical weathering and aids in moisture retention –temperate latitudes - thick layers of humus –tropics - decay so rapid that little humus accumulates –Arctic - little organic matter

Nancy Van Wagoner, Acadia University Slope Angle l On steep slopes soil is poorly developed because it gets eroded l optimum slope = flat to undulating

Nancy Van Wagoner, Acadia University Climate controls: l whether chemical or mechanic weathering dominate l amount of water available for weathering and leaching l rates of reactions (temperature dependant) l abundance and type of plants and bacteria which are available as soil forming agents

Nancy Van Wagoner, Acadia University Soil Types Fig (10.17) l based primarily on climate l classified according to the minerals present in layers A and B l 3 main types –Pedalfers –Pedocals –Laterites

Nancy Van Wagoner, Acadia University Pedalfer l form Sin areas of high rainfall l rain leaches mineral from A and B horizons l Some Fe and Al oxides in horizon B –but, not soluble material, ie. carbonate

Nancy Van Wagoner, Acadia University Pedocals l form in dry, warm climate (western US) l soil water evaporates leaving behind precipitates of CaCO3 l layer B contains pellets and nodules of CaCO3 called caliche

Nancy Van Wagoner, Acadia University Laterite l form in extremely humid regions (tropics, rain forests) l so much rain that –CaCO2 and SiO2 are completely leached –silicate minerals are completely altered –In Horizon B are insoluble oxides of Fe, and Al u Hardpan –limonite (Fe-hydroxide) –bauxite (Al-hydroxide) l poor for cultivation due to laterite and thin soil

Nancy Van Wagoner, Acadia University Tundra soil l Arctic Regions l composed of –sand and clay, some humus, and Permafrost Layer u permanently frozen ground

Nancy Van Wagoner, Acadia University Permafrost Problems l Frost Heaving - pushing of mounds of soil upward due to pressure exerted by ice, resulting in uneven, hummocky or undulating surface l Stone polygons l Engineering problems

Nancy Van Wagoner, Acadia University Rainforest Problem l –greater than half of Earth’s tropical rainforests cut u partially for timber u partly for agriculture –this is deforestation l Once vegetation is removed leaching produces poor laterite soil –limited crop production (few years), then wasteland

Nancy Van Wagoner, Acadia University Deforestation of the Tropics l continues at a rate of 7 million hectares per year