Soil Air

Question 1

What is the gaseous composition between air and soil air?

Answer 1

Atmosphere: 21% O, 0.035% CO2, 78% N,

Soil air: <21% O2, > 0.035% CO2, 78% N2

Question 2

Define soil aeration

Answer 2

Process by which air in soil is replaced by air from atmosphere

Question 3

Difference between well aerated and poorly aerated soil

Answer 3

Well aerated: exchange is rapid enough –> soil air is similar in completion to the atmosphere above soil –> no O2 deficiency or CO2 toxicity

Poorly aerated: soil contains more CO2 and less O2 than atmosphere above soil
- there is a lot of water so air diffuses very slowly in water

Question 4

Definition of oxygen diffusion rates

Answer 4

Rate af which O2 can be replenished when it is used by respiring roots or organisms or when forced out by water

Question 5

Definition of redox potential

Answer 5

Potential for the transfer of electrons from one substance to another

• a measure of the tendency of a substance to accept or donate electrons

Question 6

What happens when redox potential is high ?

Answer 6

• substance accepts electrons easily –> oxidizing agent

Question 7

What happens when redox potential is low ?

Answer 7

Substance supplies electrons waist –> reducing agent

Question 8

What are the factors affecting soil aeration ?

Answer 8

Soil water content, drainage

• volume of macropores ( soil texture, structure, bulk density, organic matter content)
• microbial decomposition of organic matter (short term : decreases the oxygen, long term: improves the structure)
• soil depth: more aeration lower down

Question 9

What are the ecological effects of soil aeration?

Answer 9

O2 deficiency, CO2 toxicity

Fertility –> oxidized forms of elements are more desirable for plants in acid soils of humid regions

Colour: oxidized Fe and Mn = dark reddish brown and black colour
- reduced Fe and Mn = blue grey