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41 Cards in this Set
- Front
- Back
Five components of mineral soil and typical percentage
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Solids:
Mineral - 50% Organic material - 1-5% Air - 20-30% Water - 20-30% Organisms - <1% |
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Porosity
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Volume/capacity for air and water in soil includes total void volume and the size and distribution of pores.
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Types of minerals in soil by size
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Sand - .05-2 mm
Silt - .002-.05mm Clay - <.002mm |
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Soil texture
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Proportion of sand, silt, and clay in a soil.
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Loam
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40% Sand, 40% Silt, 20% Clay
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Primary minerals
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Minerals that formed in the rock, inherited by the soil, e.g. quartz. Provides nutrients.
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Secondary Minerals
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Minerals formed in the soil. Usually clay sized, absorb nutrients and water.
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Forms of Organic Matter
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1. Recognizable detritus/litter
2. Humus (not recognizable)- waste from organisms 3. Colloidal material |
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Functions of organic matter
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Holds nutrients in the soil, binds particles together (aggregates), source of energy/food for organisms, holds water.
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Functions of soil water
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Holds water for roots and animals
Acts as a solvent/medium transfering nutrients from soil particles to roots Moves material through soil and out of soil - microscopically and macroscopically through layers. |
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Traits and functions of soil air
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Has higher level of CO2 and lower 02 because of respiration by soil organisms. C02 and 02 vary frequently. Relatively humidity is usually 100%. Soil aeration key to organism health.
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Traits and functions of soil organisms
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Responsible for detrital breakdown which releases and ties up nutrients and forms humus (new O.M.).
Mixes soil. Fights and contributes to disease. Changes porosity through aggregation by organism exudates and humus. Make pores as move through soil. |
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Soil profile
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Vertical cross section of a soil, that shows all the "layers" or horizons that have been altered by soil forming processes (pedogenic process)
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Horizons
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Distinct layers in the soil. Distinguished by color, texture (usually change in clay content), chemical composition.
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Master Horizons
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O,A,E,B,C,R
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O Horizon
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Organic matter
Frequently on top Common in forest soils, wetlands, not in prairie. Usually lost by tilling and in urban areas |
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A Horizon
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Mineral horizon with organic matter (humified)
Brown or black in color Usually at the surface of mineral material |
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E Horizon
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Mineral Horizon where the dominant feature is loss (of Fe, Al, O.M., clay)
Gray or whitish in color Leached or eluviated horizon |
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B Horizon
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Mineral horizon with either or both:
1. An illuvial accumulation of Fe, Al, O.M., clay - orange, yellow, light brown, or 2. Substantial alteration of original mineral material - shows pedagenic process - eliminated some rock structure, aggregated particles together, changed color to orange, yellow,grey, light brown |
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C Horizon
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Mineral horizon that hasn't changed much. Lacks the properties of O,A,E,B. Limited biological impact.
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R Layer
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Bedrock - not a horizon
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Transition Horizons
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Where changing from one master horizon to the next and has characteritics of both. E.g:
AB, BC, CB, AE - a smooth transition A/B B/C - an interfingering transition Whatever letter is first is dominant |
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Subordinate horizons
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Used to modify master horizon designations to indicate specific distinct properties within a master horizon - > lowercase letters
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Review but don't memorize common subordinate horizons
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Oi, Oe, Oa
Mineral subordinates - p,t,k, s, h, g, w B horizons are always modified with a subordinate |
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Soil colors
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Brown/black - organic matter
Red/orange/yellow - iron oxides/hydroxides White - carbonates Grey - either bare mineral grains, or anerobic conditions |
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Munsell color system
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Standard system for accurate color description. Compare soil to standard coloer chips and describe hue, chroma, and value with a system of numbers and letters.
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Sand
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Rounded, irregularly shaped or blocky
Not plastic, sticky, or moldable Large particles with large pores Drains quickly (does not hold water), highly aerated Can get coatigns of oxides, clay, O.M. and aggregate Primary mineral, inherited Very little nutrients |
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Silt
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Small particles, not visible to the eye
Slightly moldable Smaller pores than sand Some water retention and less aeration than sand. Low nutrition |
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Clay
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Usually plate or rounded
Very small particles with small pores Holds water well, poorly aerated Sticky/moldable/plasticky Large surface area Shrink - swell properties Secondary minerals and source of nutrients (Ca, MG, Fe, K) |
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Liquid and plastic limits in soil
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Plastic limit is where there is enough moisture to mold the soil. From that point until the liquid limit, soil will support some weight. At liquid limit, water content is so high the soil can't hold together and liquifies.
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What do plants need from soil
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Support
Water Nutrients O2 Temperature regulation Protection from toxics |
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Meaning of "clay"
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Clay sized particles - <.002 mm
Clay minerals - platey secondary minerals |
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Soil strength
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Capacity of soil to withstand a stress
Determined by particle size (texture), water content, minerals (clay in particular) and organic matter content |
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Soil structure - def
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arrangement of soil particles in groups or clusters - called aggregates or peds. Varies with horizon and soil type.
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Types of soil structures
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Platey - Found in any horizon. Inherited from rock or from compaction
Prismlike - Found in arid to semi arid B horizons Blocky - Found in forest B horizons Spherical or granular - Found grassland A horizons Massive - all particles stuck together Single grained - no particles stuck together |
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Causes of soil structural development
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Don't really know - the following contribute:
Climatic conditions like wet/dry cycles and freeze/thaw Clay content Oxides, O.M. and carbonates Organisms, plant roots, exudates |
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Particle density
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Density of solids in a soil - nothing to do with pores. Although changes with mineral type, small enough that we can use 2.65 g/cm3 as average density of mineral soils. Organic soils are probably less then 1 g/cm3
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Bulk Density Db
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Mass of solids in a soil per unit volume - includes pores.
Arrangement of particles can change bulk density. Db effects root growth. Density greater than 1.6 g/cm3 stops root growth. "Good" range is .08 to 1.2 g/cm3 |
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Factors that effect bulk density
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O.M. - decreases Db
Texture Loams - lower Db Volcanic ash - lower Db Compacted clay - greater Db Sand - greater Db Humus - decrease Db Plants, roots, organisms - decrease Db Plowing - decreases temporarily and ultimately increases because of loss of organic matter and compaction from equipment |
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Formula for % porosity
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100 - (Db/Dp x 100)
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Formula for Bulk Density
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Ws/V in g/cm3
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