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Reading Assignment
Chapter 7: Soil Aeration and Temperature
Too much water for too long
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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
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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%
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GASEOUS EXCHANGE
Mass flow (quicker, at shallow depth)
Diffusion (concentration gradient, more important)
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Soil properties affecting aeration
- Structure
- Texture
- Compaction
- Drainage
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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
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• If soil contains < 15% O2, plant roots begin to suffer
• < 10% O2, toxic substances may be produced
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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
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Oxidized form Reduced form
O2 H2O
NO3- N2
Fe3+ Fe2+
SO42- S2-
Mn4+ Mn2+
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How to improve Aeration?
• Improve drainage• breakup impervious layers• improve aggregation (crumb structure)• prevent crusting
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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)
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(2+) (3+)
2 FeO + 2 H2O < = > 2 FeOOH + 2H+ + 2e-
Fe(II) Fe(III)
Oxidation from divalent to trivalent (loses an electron)
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