1. Chapter 7: Soil Aeration and Temperature
Reading Assignment
Chapter 7: Soil Aeration and Temperature
Too much water for too long

2. 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

3. Composition of Air & Soil Atmosphere
Well-aerated soil
Poorly- aerated soil
Oxygen (%) 21
15-21
0-10
Carbon Dioxide
0.0375%
(375 ppm) %
(1000–5000)
1-10%
Nitrogen (%)
Relative Humidity 78
Low
Near 100%

5. GASEOUS EXCHANGE Mass flow (quicker, at shallow depth)
Diffusion (concentration gradient, more important)

6. Soil properties affecting aeration
- Structure
- Texture
- Compaction
- Drainage

7. 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

8. If soil contains < 15% O2, plant roots begin to suffer
< 10% O2, toxic substances may be produced

9. Nutrients Bright Color.................................... Dull Color
Fe+3 (oxidized)  Fe+2 (reduced)
Mn+4 (oxidized)  Mn+2 (reduced)
NO3- (oxidized)  N2 (reduced)
Insufficient oxygen
Well Oxidized: sufficient Oxygen

10. Oxidized form
Reduced form O2
H2O
NO3- N2
Fe3+
Fe2+
SO42-
S2-
Mn4+
Mn2+

11. How to improve Aeration?
Improve drainage
breakup impervious layers
improve aggregation (crumb structure)
prevent crusting

12. REDOX POTENTIAL Oxidation reduction (REDOX)
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

13. 2 FeO + 2 H2O < = > 2 FeOOH + 2H+ + 2e- Fe(II) Fe(III)
Oxidation from divalent to trivalent (loses an electron)
(2+) (3+)
2 FeO + 2 H2O < = > 2 FeOOH + 2H+ + 2e-
Fe(II) Fe(III)