Soil Temperature

Question 1

Why is soil temperature so important

Answer 1

• optimum for root growth and germination
• freeze / thaw action alters soil structure
• chemical and biological rates are low in could soils; availability of nutrients; decomposition

Question 2

Definition of temperature

Answer 2

Measure of kinetic energy of individual

Question 3

Definition of heat

Answer 3

Represents transfer of energy from one body to another, due to the difference in temperature

Question 4

How does heat transfer

Answer 4

Conduction ( through molecular collisions)

Convection ( byass movement of molecules)

Radiation ( by electromagnetic waves )

Question 5

Couriers law of hear conduction

Answer 5

G = thermal conductivity * temperature gradient

Question 6

Definition of thermal conductivity

Answer 6

Heat flow in response to a temperature gradient

Question 7

What is the thermal conductivity

Answer 7

As water content increases –> air content decreases –> transfer resistance lowered –> lambda increases

Leaf mulch has low lambda

Question 8

Heat conduction of soil and air

Answer 8

Water is good conductor

Air is a poor conductor

• dry soil is a good insulator
• heat conduction is slow –> changes in subsoil temperature lag behind surface temperature
• temperature changes less in subsoil

Question 9

Definition of specific heat of soils

Answer 9

Amount of energy required to raise the temperature of a substance by 1 degree dlon a unit mass basis

Question 10

Specific heat of soil and air

Answer 10

Water has high heat capacity
Air has low heat capacity

Question 11

Heat capacity of water and air

Answer 11

Water has high heat capacity

Air has low heat capacity

Question 12

Definition of heat of vaporization

Answer 12

Evaporation of water from the soil surface required a large amount of energy

Energy comes from soil radiation and surrounding soil -> has the potential cool the soil

Low temperature of wet soil in the day in the spring / summer –> due to evaporation and specific heat ( in spring -> wet would are 3 to 6 degrees cooler than dry soils )

Question 13

How does soil temperature vary with depth?

Answer 13

• surface layer temperature varies according to air temperature –> usually warmer than air
• subsoil temperature lags behind changes in the surface temperature -+> warmer in winter and cooler in summer than surface –> not affected directly by solar radiation

Question 14

List 2 to 3 different ways you can control soil temperature

Answer 14

Organic mulch buffers extremes in temperatures
- in hot weather –> keep surface soil cooler
- in cold weather –> moderate rapid temperature decrease

Organic mulch and plant residues
- conservation tillage –> leave residue at surface –> cooler soils in July / Aug
- low temperature in May / June –> may decrease germination
- decrease evaporation of water

Question 15

Describe how plastic mulch work

Answer 15

Increase soil temperature –> good in spring; root growth may decrease in summer

• use for water management and weed control
• gardens, high value crops –> can extend the growing season and hasten growth

Question 16

Describe moisture control for soil temperature control

Answer 16

Wet would in spring are 3 to 6 degrees cooler than dry soils
- control methods:
-install drainage system
- ridge the soil