Soil Atmosphere - ANSWERVaries from atmosphere
Contains 2 main gases (CO2/O2) needed for the two most important biological processes (photosynthesis and respiration)
Photosynthesis - ANSWERConsumes CO2 and H2O and releases O2 and produces sugars
Respiration - ANSWERConsumes O2 and releases C...
SCSC 301 Exam 2 – Howe Questions &
Answers(RATED A+)
Soil Atmosphere - ANSWERVaries from atmosphere
Contains 2 main gases (CO2/O2) needed for the two most important biological
processes (photosynthesis and respiration)
Photosynthesis - ANSWERConsumes CO2 and H2O and releases O2 and produces
sugars
Respiration - ANSWERConsumes O2 and releases CO2, H2O, and energy
Oxygen Availability - ANSWERRegulated by...
1. Soil macroporosity
2. Soil water content
3. Oxygen consumption by respiring organisms
Movement of Oxygen - ANSWERMass flow - movement due to different total
pressure
Diffusion - movement due to difference in partial pressure
Excess Water - ANSWERWater saturated or waterlogged soils have all or nearly all
pores filled with water
- O2 is depleted quickly by microbes and plants
- Soil is anaerobic
- Some plants have adapted (rice), most have not
- Microbes - aerobic microorganisms cannot carry out processes under these
conditions
When are activities of aerobic organisms are usually affected? - ANSWERWhen
pores are <20% air or <10% of total soil volume
Oxygen Diffusion Rate (In water) - ANSWER10,000x slower than oxygen diffusion
via air
Soil Structure and Air Movement - ANSWERSoil structure, especially in clayey soils,
is important indetermining O2 movement
- Clayey soils with good aggregation have plenty of macropores that allow water to
drain
- Micropores generally trap water or slow it down
How to Improve Aeration? - ANSWER- Improve drainage
- Reducing compaction
- Tillage - Important in A horizon, but may compact below the plow line
Factors Affecting Aeration - ANSWER- Drainage
- Rates of Respiration (affected by organic matter inputs and T)
- Depth in profile
What happens when poor aeration occurs? - ANSWER- Organic residue
decomposition slows
- Changes in nutrients
- Toxicity of some elements changes
- Soil color changes
- Methane production (formed by anaerobic bacteria & fungi)
- Reduces plant growth and sometimes causes death
Processes Affected by Soil Temperature - ANSWERLow temperatures slow
chemical and biological processes (Plant growth, plant uptake of water,
decomposition of OM, nutrient cycling)
Very high temperatures can inhibit plant and microbial processes
Soil temperature also affects engineering considerations
Thermal Properties of Soil - ANSWERSpecific Heat
Thermal conductivity
Specific Heat - ANSWERAmount of energy to raise T by 1°C per g
Soil water > soil solids >> soil air
- Wet soils will require more energy to warm than dry ones
Thermal Conductivity - ANSWERMovement (or rate) of heat through soil
Influenced by
• Water content (high water conducts heat)
• Compaction (high compaction conducts heat)
Soil solids > soil water >> soil air
- A wet, compacted soil is the best conductor
- Dry soils are generally good insulators
Soil Temperature Control - ANSWEROrganic residues or mulch on soil surface
- Reduces erosion
- Buffers extremes in temperatures
- Keep soil cool in hot weather
- Keep soil warm in cold weather
Soil Water - ANSWERProperties largely due to structure of water
Formula - H2O
Arrangement is not linear
Angle between H-O-H is 105° (lone pairs)
Causes polarity - charges are not evenly distributed
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