Hunter & Benny K DIRT pt2

What is the difference in composition between soil air and atmospheric air and what are the main reasons for this difference.

Soil air - less oxygen, more CO2

Atmospheric air - N2 79%, O2 21%, >CO2. water vapor 10-90%

What is the role of gas diffusion in explaining differences between soil and atmospheric air composition.

there is less oxygen because it is bing turned into CO2

Total porosity

Volume of pore space per total volume (Vp=Va+Vw)

Volumetric air content

Volume of air space pe total volume (Va/Vt)

Volumetric water content

Volume of water per total volume (Vw/Vt)

What is bulk density

dry weight of soil per unit of total volume (pb=Ms/Vt)

Particle density

Is the mass of solids per unit volume of the solids (ps=Ms/Vs)

What is the relationship between bulk density and porosity

It’s in an inverse relationship, as BD increases, P decreases

What is the difference between volumetric and gravimetric water content

volumetric - volume of water per total soil volume

gravimetric - mass of water per mass of dry soil

What are the unique properties of water?

polar, hydrogen bonding, cohesion, adhesion

Why is water attracted to charged surfaces/ions

Because it is polar!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

saturation

soil: all the pores are filled with water

field capacity

moistrure content after 24 to 48 hours of drainage by gravity

Permanent wilting point

moisture content after plants wilt and do not recover upon rewetting

available water

relationship between field capacity and permanent wilting point

What are cation exchange capacity (CEC)

displacement of one absorbed cation for another from the soil solution, net negitive charge that attracts cations

anion exchange capacity (AEC)

AEC is usually much lower than CEC in temperate non volcanic ash soils,net positive charge that attracts anions

Base saturation

the sum of exchangeable base cations divided by the sum of all exchangeable cations

How do ion valence and ion size affect adsorption to charged surfaces

higher charge = higher atraction

smaller size = closer to the surface

What is cation exchange and mass action

Cations trade places, and mass action pushes the reaction toward whichever ions are more abundant.

specific adsorption

amount of absorbed anions exceeds the amount of positive surface charge

ligand exchange

represent a specifc anion absorption mechanism

metal sorption

absorption of polyvalent metals on surfacrs of Mn & Fe oxides; metal is immobilized

surface chelation

may be more mobil if organic molecure is soluble

What is the role of Al in soil acidification?

Acdic soils have high levles of exchangeable Al+3 from the dissolution of alumina-silicates

What is the best pH range for most plants

5.5-8.5

How does pH affect plant growth

Low pH is more toxic

high pH more deficiency