Soil Aeration
What five processes make up the energy balance at the surface of a soil. How do they change from day to night?
1. Reflection 2. Conduction 3. Evapotranspiration 4. Thermal Radiation 5. Heating At night, heat is only gained from sky radiation. Reflection also is reduced. Since inputs no longer keep up with heat outputs, soil cooling occurs at the surface, and the direction of soil heating changes
water
1000cal/kg
Dry soil
200cal/kg
O2 Content (measurement)
Amount of air x concentration of o2 in air water holds only small amount of o2
Soil Respiration
CH2O+O2=CO2 +H2O consumes o2 produces co2 soil microorganisms > plant roots > soil animals
Color of Soil Surface-Soil heating
Darker soils absorb more heat
O2 Gradient
Decreases with depth due to O2 consumption gradient with depth
Inputs (2)
Direct solar radiation sky radiation
Dry VS Wet soil
Dry soil heats more rapidly
Outputs (4)
Evapotranspiration Thermal radiation Reflection Conduction
Factors affecting aeration (7)
Excess moisture Soil texture Poor Structure Position on Slope Impermeable layers soil depth O2 consumption
Heat of Vaporization
Heat required to evaporate water 540cal/g heat comes from soil=soil is cooled heat usually comes from radiation, evap prevents soil heating wet soils 3-6 degrees cooler then moist
Specific Heat
Heat required to raise temp from 15 degrees to 16 degrees increases with moisture content
Soil Energy Balance (inputs/outputs)
If energy input is greater than output=soil heating If energy in put is less than output =soil cooling
Resistance
Increases with reduction in pore size
Mechanisms of gas movement
Mass Flow Diffusion
Soil Aeration
Mechanism of Gas exchange in soils Prevents O2 deficiency Prevents CO2 toxicity
Mass Flow
Movement of mass air/gasses move together driven by pressure gradients caused by changes in temp/pressure also caused by movement of water downwards
Insulating materials
Mulch snow forest floor
Idea Gas Law
PV=nRT (mass flow)
O2 diffusion rate (ODR)
Rate of movement across a cross-sectional area gradient and resistance are function of this concentration
Effects of poor soil Aeration (7)
Root growth curtailed Nutrient uptake reduced Water uptake reduced methanogenesis Toxic compounds form changes of soil color Aerenchyma
Wet soil
Somewhere in between
Aspect-Soil Heating
Southwest facing slopes warmer
Ecological redox sequence
Strongest oxident will drive reaction after o2 consumed through aerobic respirtation other terminal acceptors replace it controlled by different classes of bacteria landfills/production of methane?
Soil Temperature
a manifestation of the soil energy content Higher temp=more radiation Higher temp=shorter wave length
Slope-Soil heating
becomes greater as angle of incidence approaches perpendicular
Vegetation-Soil heating
changes color shades soil more evapotranspiration=cooling
Diffusion
each gas moves down gradients of its own concentration no overall pressure differences partial pressure O2 Co2 opposite directions
Conduction
intermolecular energy transfer vibrational energy
If a soil atmosphere has a CO2 concentration of 10%, then the O2 concentration and n2 would be
n2-80% o2-20%
Redox potential (Eh)
oxidation-reduction potential affinity of a substance for electrons
three processes which might limit Oxygen Diffusion Rates in a soil. How low would these rates have to be before root growth is limited.
root depth poor size labile organic matter at the surface (mulch)