Soil Science Exam 2- Aeration and Temperature

T/F: Soil air is different from atmospheric air

TRUE: Because O2 is required in respiration and for organic material decomposition, soil air is different from atmospheric air. Some O2 is used and considerable CO2 is produced.

Why do water filmds inhibit O2 diffusion

O2 diffusion through soil is inhibited by water-filled pores because the diffusion coefficient for O2 is about 10,000 times less through water than through air

What are the progressive stages of soil anoxia?

Oxygen reduction -> Nitrogen reduction -> Iron Reduction -> Mn Reduction -> Sulfate reduction -> Methanogenesis

How does soil become anaerobic? i.e. What must occur?

1) Oxygen diffusion must be restricted (compaction, moisture- saturation)

2) Oxygen must be consumed (respiration)

Ecological consequences of soil aeration status

- Impacts plant growth

- plants differ in tolerance to wet soils

- Modifies decomposition of organic residues

- poor aeration slows decomposition

- Can cause buildup of toxic organic compounds

- Alters oxidation states of elements

- Plant nutrients

- Toxic elements

- Soil colors

- Production of greenhouse gases

T/F: Wetlands commonly have anaerobic soil conditions

True! The soils are water saturated for prolonged periods and certain plants and microbes can grow and remove the soil oxygen.

- Wetlands have reduced in land area by more than 50% since European settlement began

What are the values of welands?

- Species habitats

- Water filtration

- flooding reduction

- Shoreline protection

- Commercial/recreation activities

- Natural Products

What are the 3 indicators of wetland systems?

1) Wetland hydrology or water regime

- requires year round monitoring wells

2) Hydrophytic Plants

- not always present

- some have specialized structures (aerenchyma, Adventitious roots, Knees)

3) Hydric soils

- Probably most useful

- Have aquic moisture regimes (aquept)

5 features of hydric soils

- Gray colors (gleying)

- Black organic matter accumulation

- Fe/Mn Nodules

- Gleying with mottles

- red oxidized root zones of hydrophilic plants

T/F: Air temperature affects plants more than soil temperature

FALSE: Soil temperature affects plants more than air temperature. A combination of both air and soil stress has the worst effects on plant growth.

the Q-10 principle

The rate of many chemical and physical biological processes (including weathering) about double for each 10 degree C increase in temperature (within limits)

T/F: Dry soil is more easily heated than is wet soil on a weight basis

True! Soil has a much lower specific heat than water does. BUT, wet, compacted soils conduct heat more readily/uniformly than non-compacted or dry soils, despite heating more slowly.

- soil temps become more consistent with increasing depth

What is the benefit of plastic mulches over organic mulches

Plastic mulches serve to warm soils in early spring, unlike organic mulches. CLEAR plastic has a GREATER heating capacity than black plastic.

T/F: During hot weather, heat generation under plastic mulches can reduce plant growth

TRUE

Frost Heaving

The upward swelling of soil caused by the formation of ice lenses as freezing conditions penetrate the ground. Water is drawn to the freezing front by capillary action and freezes, creating ice that pushes the soil and anything in it (like plants or foundations) upward.