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Midterm review

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Alison Smith

Lecture 1 1) What is soil? The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of plants. 2) What are the differences between the solum and regolith? Solum: the upper and most weathered part of the soil profile, the A,E and B horizons. Regolith: the unconsolidated mantle of weathered rock and soil material on the earth surface. Loose earth materials above solid rock. 3) What are the six main ways soils function in natural and managed landscapes? Describe each briefly. Medium for plant growth, recycling system for nutrients and organic wastes, modifier of the atmosphere, habitat for soil organisms, engineering medium, system for water supply and purification, 4) What five factors influence soil development? 1) Parent materials 2) Climate 3) Topography 4) Time 5) Biota 5) define the term soil profile - soil scientists often dig a large hole called soil pit, usually several meters deep and about a meter wide to expose soil horizons for study. The vertical section exposing a set of horizons in the wall of a pit 6) what are the five soil horizons most commonly found in humid forested regions of Ontario? 1) O-organic layer at soil surface, organic materials formed from fallen leaves and other plants and animals remains accumulating on the surface that undergo varying degrees of physical and chemical breakdowns and transformation, so these layers of older, partially decomposed materials may underlie , the freshly added debris 2) A- soils animals and percolating water move some of these organic materials downward to intermingle with mineral grains of the regolith. These join the decomposing remains of plant roots to form organic matter that darken the upper mineral layers, also because weathering tends to be most intense nearest the soil surface, in many soils the upper layers loose some of their clay or other weathering products by leaching to horizons below A horizons are the layers nearest the surface that are dominated by mineral particles but have been darkened by the accumulation of organic matter. 3) E- intensely weathered and leached horizons that have not accumulated organic matter occur in the upper part of the profile, usually just below A horizon 4) B- varying amounts of silicate clays, iron, Al, oxides, gypsum, calcium carbonate may accumulate in here, washed down from horizons above, formed thru weathering =subsoil 5) C-plant roots and microorganisms often extend below B, especially in humid regions causing chemical changes in soil water, some biochemical weathering of the regolith, the formation of C horizons=least weathered part of the profile. 7) in an ideal loam soil, what is the relative volume occupied by major constituents? -mineral 45% -organic matter 5% -air and water 20-30% for each 8) what soil particles contribute to soil texture designations? Sand clay silt 9)how does soil organic matter affect soil texture? -physical chemical difference 10) define an essential element. -organic matter binds mineral particles into a granular soil structure that is largely responsible for bose, easily managed conditions of productive soils. -imp for stabilizing granules -(+) amount of water a soil can hold -plant growth abundant OM including plant roots helps create physical conditions favourable for growth of higher plants and microbes contrasting, soils low in OM, especially high in silt and clay are often cloddy and not suitable for optimal plant growth -essential element: constant replenishment -absorb nutrients in solution -bulk of nutrients locked up in structural framework of primary minerals, org matter, clay, humus 11) Where is the pedosphere located relative to the atmosphere, lithosphere, atmosphere and biosphere? a) at km scale, soil participates in global cycles and the life of terrestrial ecosystems, atmosphere b) at m scale, soil forms a transition zone between the hard rock below and the atmosphere above-a zone thru which surface water and groundwater flow and in which plants and other living organisms thrive- biosphere c) mm, mineral particles form the skeleton of the soil that defines pore space, some filled with air and some with water, in which tiny creatures lead there livesd) micronanometer scakes, soil minerals (litho) provide charges, reactive surfaces that adsorb water and cations dissolve in water (hydrosphere) gases (atmos), bacteria and complex humus (macromoecues, biosphere Lecture 2 1) how were the following parent materials formed, transported or deposited? Till: materials deposited directly by ice Loess:wind blown material, main sources were the great barren expanses of till and out wash left in Missouri and Mississippi river valleys by the retreating glaciers of the last ice age Outwash plains: in valleys and on plains where the glacial waters were able to flow away freely Lacustrine: when ice came to a stand still, where there was no ready escape for the water, pounding began, ultimately large lakes were formed Marine: over time sediment builds up on ocean floor Colluvium: made up of poorly sorted rock fragments detached from the heights above and carried downslope, mostly by gravity Aeolian: very fine particles, Residual: developed from weathering of the underlying rock Alluvium: from streams that leave a narrow valley in an upland area and suddenly descend to a mu
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