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38 Cards in this Set
- Front
- Back
Factors that efffect soil heating from solar energy
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Aspect, vegetative cover, color/albedo
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Which soil warms faster - wet or dry?
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Dry. Wet soil such as in the spring warms more slowly
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cal/gram of energy need to raise the temperature of water 1 degree, and mineral soil?
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1 cal/gram H20
.2 cal/gram soil |
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Methods of providing energy for soil cooling through evaporation
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Solar energy
Soil heat Long wave radiation from earth |
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Amount of energy needed to evaporate 1 g of water
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540 g
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How does heat move through soil?
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By conduction. From areas of heat(energy) to cooler areas (less energy).
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Most conductive to least conductive elements of soil
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Water - Mineral soil - air
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Paradox of the role water plays in the movement of heat through soil.
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Water enhances heat transfer through high conductivity but requires more energy to get hot in the first place
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Describe soil variability
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Varies by season, depth, location but in predictable patterns. More variable at the surface, lag time for max and min temps.
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How do humans impact soil temperature?
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Remove vegetation which broadens extremes. Mixing which removes insulating organic horizons. Buildings and pavement heat up nearby soils. Irrigaion adds H20.
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Properties of organic and plastic mulches
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Organic mulches tend to cool the soil and reduce temperature fluctuations. Plastic mulches heat the soil, clear more than black, but black keeps light from causing seed germination.
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Typical percentages of soil air compared to the atmosphere.
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Atmosphere is 21% O2 and .03% CO2. Soil air variers from 5-20% O2 and .35 to 10% CO2.
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Other gases besides O2 and CO2 that are found in soil.
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N20, H2S, methane - products of organic decomposition - especially anerobic.
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Why is soil O2 lower?
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Plant root respiration and limitation on soil air movement
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The process of soil aeration is
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the exchange of soil gases with gases in the atmosphere. Release CO2, absorb O2.
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Two methods of soil aeration
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Mass flow and Diffusion
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Mass Flow
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Bulk movement of air, no gas exchange. Happens mostly in macropores (.08mm or bigger). Rapid.
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Diffusion
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Gas exchange from areas of high concentration to low concentration. Happens in both macro and micro pores. Slow. Only method of aeration in micropores
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Why is soil aeration important?
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Oxygen is needed by roots and microorganisms to respire and make energy to take up nutrients. As O2 goes down, switch to more anerobic, lower energy reactions, slows decomposition, plant ability to take up nutrients.
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Key to good soil aeration is
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Maintaining soil aggregates (macropores) and reducing barriers.
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Polarity of water
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Water is slightly positive on H side and slightly negative on O side.
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Hydrogen bonding
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Bonding of H side of water to other cations or other water molecules.
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Cohesion
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Desire of water molecules to stick together - results from polarity and hydrogen bonding.
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Adhesion
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Tendancy of water to stick to surfaces because of polarity - surface tension.
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Capillarity
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How water is drawn up a small tube or through small spaces in soil because of cohesion and adhesion. Inverse relationship between height of water and radius of the capilary.
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Factors effecting soil water movement
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capilarity and gravity
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Soil water potential energy
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Refers to the relative ability of water to do work in soil relative to a reference state of pure water
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What is the reference state for measuring soil energy potential?
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Pure water
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Components of soil water potential
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Elevation - gravity
Adhesion and cohesion - matric Dissolved salts - Osmotic potential Pressure |
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Describe gravity as a component of soil water potential
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Moves downhill (high to lower energy). Always positive value.
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Describe matric potential as a component of soil water potential
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Water bound by cohesion or adhesion has less energy - is a negative value compared to the reference state. Water moves from saturated to unsaturated areas of soil.
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Types of water flow in soil
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Saturated and unsaturated. Also vapor -rare.
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Saturated flow
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Fast. Happens when all pores filled. Moves with gravity.
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Unsaturated flow.
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Slow. Happens when all pores are not filled. Moves laterally and up with capilarity - wet to dry.
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Saturated vs unsaturated flows in course and fine soil.
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Course soil quickly gets saturated and flows quickly down. Fine soil takes flows through unsaturated flow for a long time before becoming saturated.
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Field capacity (FC)
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When all free water is drained from a soil over a short period time (48 hours). Macropores are empty.
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Permenant wilting point (PWP)
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Point where plants are unable to get water from soil. What water remains it too tightly held by adhesion/cohesion.
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Available water
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The difference between field capacity and permenant wilting point.
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