Chapter 5 - Physical Characterisitcs Of Soil

Question 1

What does soil consist of

Answer 1

Mineral matter 45%
Air 25%
Water 25%
Organic matter 5%

Question 2

What is ion exchange

Answer 2

Takes place in soils where ions are attracted to soil particles and are held on the surface of these particles
Also know as adsorption

Question 3

What is organic matter and humus

Answer 3

Organic matter - the remains of plants and animals

Humus - the dark coloured decomposed plant and animal matter found in the soil. It is rich in nutrients and contributes to soil structure

Question 4

What is soil texture

Answer 4

Is a measure of the proportion of sand silt and clay in a soil sample
Important as it cannot be changed

Question 5

What is Loam soil

Answer 5

A soil that has equal amounts of sand silt and clay

Question 6

What are the five physical properties of soil

Answer 6

Texture 
Structure 
Porosity and density 
Colour 
Temperature

Question 7

What is flocculation and how does it occur

Answer 7

The clustering together of soil particles to form floccules
The floccule is a chain of collided particles held together forces of attraction between water and colloids
The floccule then trap larger particles such as sand and silt forming aggregates

Question 8

What is cement action and separation

Answer 8

Cementation - the binding together of soil particles

Separation - occurs when soil aggregates are separated within the soil

Question 9

What is soil porosity

Answer 9

Refers to the total volume of soil occupied by soil pores
Good soil should have 50% of its volume occupied by soil pores
Pores are filled with air and water

Question 10

How does soil compaction occur

Answer 10

Occurs when soil particles are pressed together aggregates are destroyed which reduces pore space

Question 11

What is absorbed water (hydroscopic water)

Answer 11

A positively charged water that forms a thin film around a negative soil particle
It cannot be removed from soil and is unavailable to plants

Question 12

What is capillary water and gravitational water

Answer 12

Capillary water - held in by the pores when the soil aggregates and in the pores between the soil aggregates

Gravitational water- moved through the soil by gravity

Question 13

What is field capacity and permanent wilting point

Answer 13

Field capacity - amount of water in a soil after the gravitational water has been drained away

Permanent wilting point - the point at which no more capillary water can be removed from the soil by plants

Question 14

What is Available water capacity

Answer 14

Field capacity - permanent wilting point

Question 15

What does soil colour indicate

Answer 15

The amount of humus and parent material content
High humus = good soil structure
Dark soils absorbs more sunlight so heat up quickly
Grey - lacking humus low fertility leeching
Red - presence of iron may have been leeched to form an iron pan

Question 16

What is soil temperature

Answer 16

The rate of chemical reaction doubles with every 10*C rise in temperature so the warmer the soil the faster the growth rate

Question 17

What is soil erosion

Answer 17

Removed topsoil from the surface of the land
This can happen by wind water and tillage erosion
Can be reduced by employing min-till operations installing drainage and by the use of catch crops

Question 18

What is carbon sequestration

Answer 18

The removal of carbon dioxide from the atmosphere by plant photosynthesis and storing as plant biomass and organic soil matter

Question 19

What are the five types of mineral particles found in soil

Answer 19

Gravel
Coarse sand
Fine sand
Silt and clay

Question 20

Minerals matter

Answer 20

Gravel and sand lead to good drainage and aeration

Silt and clay are good for water retention and clay and has high fertility levels

Question 21

Factors that affected structural development

Answer 21

Freezing and thawing 
Soil organic matter 
Animal activity 
Wetting and drying 
Plant root activity 
Cultivation and tillage