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)