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20 Cards in this Set
- Front
- Back
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O Horizon |
Organic horizon -dominated by organic material -on the soil surface usually -usually not described in many soils, since they are thin, and rapidly change -in peats and mucks, the O horizon extends almost to the bottom of the soil |
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A horizon |
a mineral horizon -at surface, or just below the O horizon -might contain some organic material mixed in with the mineral material -can reflect plowing, pasturing, other activities |
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E horizon |
a mineral horizon -"eluviation" horizon -Major characteristics include: loss of clay, iron and aluminum oxides, and salts via eluvation -Eluvation=leaching -An increase in concentration of sand and silt size particles of resistant minerals -Lighter color than A horizon |
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B horizon |
a mineral horizon -"illuviation" horizon -Accumulation of materials -Clay, iron and Al oxides, calcium and sodium salts from overlying horizons |
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C horizon |
a mineral horizon -consists of unconsolidated, partially weathered material (neither soil nor rock) -below zone of biological activity -upper part of C may become part of B horizon |
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R layer |
underlying consolidated bedrock |
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Vermiculite |
a 2:1 layered phyllosilicate more Isomorphic substitution than smectite; charge of -.6 to -.9, letting in more cations moderate shrink-swell |
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Smectite |
2:1 phyllosilicate not as much iso-sub. as vermiculite, hence there is less cation "glue to hold layers together, allowing more water in between layers, giving way to HIGH shrink-swell properties |
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uses for smectite |
cat litter sealing up landfills fertile soils (hard to manage due to shrink/swell) |
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uses for vermiculite |
potting soil |
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Sapric Hemic Fibric |
Bulk density: >0.2-1.0 g/cm3 ~0.1g/cm3 |
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what makes soils more acidic |
-OM: weak acidic groups dissociate, add H+ to soil -Al3+ and Fe3+ hydrolyze H2O, produce H+ -NH4: nitrification (oxidation) of ammonium with O2 produces H+ -Carbonic acid (H2CO3): created when H20 interacts with CO2; then dissociation into H+, HCO3...H+, CO3 -Roots also contribute protons to soil as they pump in nutrients in the form of cations (Ca2+, K+) -N fertilizers (NH4+) cause nitrificaiton -Acid rain (SO2, NOx) by burning coal |
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Sources of OH- in soils |
1. Carbonate salt dissolution -CaCO3, Na2CO3 plus H2O |
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Optimal soil acidity
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5.5-7 |
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how can you raise soil pH |
adding lime (CaCO3) |
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how can you lower soil pH |
add sulfur, organic matter |
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Sandy soil |
low in nutrients drought-prone |
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Silty |
prone to erosion |
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Clay |
good nutrient retention primary minerals |
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Fine earth fractions: sand, silt, clay |
are less than 2mm in diameter: sand: >2-0.05mm silt: 0.05-0.002mm clay: <0.002mm |
