Reading Assignment

Chapter 7: Soil Aeration and Temperature

Too much water for too long

Aeration relates to:

Ventilation of soil with air (moving in and out of soil)

The rate of gas exchange with atmosphere

Proportion of pore spaces filled with air

Composition of soil air

Potential for oxidation and reduction (“redox”) within soil

Moisture status of soil

Temperature of soil

Survival of plants or vegetation

Composition of Air & Soil Atmosphere

Air Well-aerated soil

Poorly- aerated soil

Oxygen (%) 21 15-21 0-10

Carbon Dioxide

0.0375%

(375 ppm)

0.1-0.5%

(1000–5000)

1-10%

Nitrogen (%)

Relative Humidity

78

Low

78

Near 100%

78

Near 100%

GASEOUS EXCHANGE

Mass flow (quicker, at shallow depth)

Diffusion (concentration gradient, more important)

Soil properties affecting aeration

- Structure

- Texture

- Compaction

- Drainage

 Effect of poor aeration on plants and soil properties

- As gas exchange is slowed, CO2 produced by organisms cannot escape fast enough and O2 required by organisms cannot enter fast enough

- Other gases (H2S, methane, ethylene, etc.) produced by organisms can accumulate and maybe harmful to organisms and change soil chemical properties

• If soil contains < 15% O2, plant roots begin to suffer

• < 10% O2, toxic substances may be produced

NutrientsBright Color.................................... Dull Color

Fe+3 (oxidized) -------------------- Fe+2 (reduced)

Mn+4 (oxidized) --------------------- Mn+2 (reduced)

NO3- (oxidized) ---------------------- N2 (reduced)

Well Oxidized: sufficient Oxygen Insufficient oxygen

Oxidized form Reduced form

O2 H2O

NO3- N2

Fe3+ Fe2+

SO42- S2-

Mn4+ Mn2+

 How to improve Aeration?

• Improve drainage• breakup impervious layers• improve aggregation (crumb structure)• prevent crusting

REDOX POTENTIAL

• Soil REDOX potential is a measure of a soil's ability to lose or gain electrons

• Oxidation is the major mechanism of energy generation by organisms – Oxygen is required for respiration by plants and animals

• The consumption of oxygen by biota is what reduces the REDOX potential in soil

Oxidation reduction (REDOX)

(2+) (3+)

2 FeO + 2 H2O < = > 2 FeOOH + 2H+ + 2e-

Fe(II) Fe(III)

Oxidation from divalent to trivalent (loses an electron)