Soil Aeration Flashcards
Purposes of soil aeration
- Supply oxegen to plant roots (respiration)
- Allow release of toxic gases
1. methane
2. ethylene
3. CO2
pore aeration
Anytime O2 levels become insufficient in the root zone to support plant growth
Plant growth impact zone
Around 0.1 L O2/L
Factors that affect soil aeration
- Macroporosity
- soil water content
-O2 Consumption
Water saturated soil are ____________ to plants
Usually not favorable to plants
What plants are good for water saturated soils
Mangrove trees, rice, and cattails
Adaptions for plants that can live in water saturated soil
growing roots above the water, Aerenchyma
Composition of soil air- Oxygen
0-20%
Composition of soil air- Nitrogen
78% N2 (same as atmosphere)
Composition of soil air - Carbon dioxide
0.3-10% CO2 Above 10% can be toxic to plants
Other gases that are contained in soil
Methane (CH4), Hydrogen sulfide (H2S), Ethylene (C2H4) ( products of anaerobic microbes)
Main source of gas movement in soil
Diffusion
Movement from areas of _____ partial pressure to areas of _____ partial pressure
high low
Comparison of soil to atomosphere O2
O2 is higher in atmosphere than in soil
Comparison of soil in atomosphere CO2
CO2 is higher in soil than atmosphere
Why is O2 deficiency a problem in wet soils?
Water filled pores block the diffusion of oxygen to replace what is used by respiration
How do soil oxygen sensors work
Works using a membrane and partial pressure difference
Air filled porosity
Percentage of total pore space occupied by air
When does microbial activity and plant growth decrease
if air fill pores is below 20%
air filled porosity equation %
((total porosity- volumetric soil water content) / total porosity) * 100
In well aerated soil, ______ compounds are dominant
oxidized
FeOOH- Fe(III)
NO3 - N (V)
In poorly aerated soil, ______ compounds are dominant
Reduced
FeO - Fe (II)
NH4+ - N (III)
Redox reaction
When a reduced state of a an element Is changed to oxidized state
Substances that accept electrons are called
oxidizing agents ( O2 )
Substances that supply electrons are called
Reducing agents (Fe+2)
As oxygen content of soil decreases, redox potential _______
decreases
When O2 is not present
Must use another substance as terminal electron acceptor for their metabolism
Why is redox potential important
- Provides specific info on chemical species present in soil
- nutrient availability
- Mobility of nutrients/ Pollutants
-Toxicity of certain elements - corrosively of soil
Factors affecting soil aeration
- Drainage of excess water through macropores
- respiration rates
- warm vs cold season
- saturated vs moist vs dry
- Organic amendments vs none
- Depth
- tillage
