Soil Aeration

Question 1

Purposes of soil aeration

Answer 1

• Supply oxegen to plant roots (respiration)
• Allow release of toxic gases
  1. methane
  2. ethylene
  3. CO2

Question 2

pore aeration

Answer 2

Anytime O2 levels become insufficient in the root zone to support plant growth

Question 3

Plant growth impact zone

Answer 3

Around 0.1 L O2/L

Question 4

Factors that affect soil aeration

Answer 4

• Macroporosity
• soil water content
  -O2 Consumption

Question 5

Water saturated soil are ____________ to plants

Answer 5

Usually not favorable to plants

Question 6

What plants are good for water saturated soils

Answer 6

Mangrove trees, rice, and cattails

Question 7

Adaptions for plants that can live in water saturated soil

Answer 7

growing roots above the water, Aerenchyma

Question 8

Composition of soil air- Oxygen

Answer 8

0-20%

Question 9

Composition of soil air- Nitrogen

Answer 9

78% N2 (same as atmosphere)

Question 10

Composition of soil air - Carbon dioxide

Answer 10

0.3-10% CO2 Above 10% can be toxic to plants

Question 11

Other gases that are contained in soil

Answer 11

Methane (CH4), Hydrogen sulfide (H2S), Ethylene (C2H4) ( products of anaerobic microbes)

Question 12

Main source of gas movement in soil

Answer 12

Diffusion

Question 13

Movement from areas of _____ partial pressure to areas of _____ partial pressure

Answer 13

high low

Question 14

Comparison of soil to atomosphere O2

Answer 14

O2 is higher in atmosphere than in soil

Question 15

Comparison of soil in atomosphere CO2

Answer 15

CO2 is higher in soil than atmosphere

Question 16

Why is O2 deficiency a problem in wet soils?

Answer 16

Water filled pores block the diffusion of oxygen to replace what is used by respiration

Question 17

How do soil oxygen sensors work

Answer 17

Works using a membrane and partial pressure difference

Question 18

Air filled porosity

Answer 18

Percentage of total pore space occupied by air

Question 19

When does microbial activity and plant growth decrease

Answer 19

if air fill pores is below 20%

Question 20

air filled porosity equation %

Answer 20

((total porosity- volumetric soil water content) / total porosity) * 100

Question 21

In well aerated soil, ______ compounds are dominant

Answer 21

oxidized
FeOOH- Fe(III)
NO3 - N (V)

Question 22

In poorly aerated soil, ______ compounds are dominant

Answer 22

Reduced
FeO - Fe (II)
NH4+ - N (III)

Question 23

Redox reaction

Answer 23

When a reduced state of a an element Is changed to oxidized state

Question 24

Substances that accept electrons are called

Answer 24

oxidizing agents ( O2 )

Question 25

Substances that supply electrons are called

Answer 25

Reducing agents (Fe+2)

Question 26

As oxygen content of soil decreases, redox potential _______

Answer 26

decreases

Question 27

When O2 is not present

Answer 27

Must use another substance as terminal electron acceptor for their metabolism

Question 28

Why is redox potential important

Answer 28

• Provides specific info on chemical species present in soil
  
  • nutrient availability
  • Mobility of nutrients/ Pollutants
    -Toxicity of certain elements
  • corrosively of soil

Question 29

Factors affecting soil aeration

Answer 29

• Drainage of excess water through macropores
• respiration rates
  
  • warm vs cold season
  • saturated vs moist vs dry
  • Organic amendments vs none
• Depth
• tillage