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
Oxygen (%)
Carbon
Dioxide
Nitrogen (%)
Relative
Humidity
Air
Well-aerated
soil
Poorlyaerated soil
21
15-21
0-10
0.0375%
(375 ppm)
0.1-0.5%
(1000–5000)
1-10%
78
78
78
Low
Near 100%
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
Nutrients
Bright 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
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
Oxidation from divalent to trivalent
(loses an electron)
(2+)

(3+)
2 FeO + 2 H2O < = > 2 FeOOH + 2H+ + 2eFe(II)
Fe(III)