Chapter 5 - Physical Characterisitcs Of Soil Flashcards
What does soil consist of
Mineral matter 45%
Air 25%
Water 25%
Organic matter 5%
What is ion exchange
Takes place in soils where ions are attracted to soil particles and are held on the surface of these particles
Also know as adsorption
What is organic matter and humus
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
What is soil texture
Is a measure of the proportion of sand silt and clay in a soil sample
Important as it cannot be changed
What is Loam soil
A soil that has equal amounts of sand silt and clay
What are the five physical properties of soil
Texture Structure Porosity and density Colour Temperature
What is flocculation and how does it occur
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
What is cement action and separation
Cementation - the binding together of soil particles
Separation - occurs when soil aggregates are separated within the soil
What is soil porosity
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
How does soil compaction occur
Occurs when soil particles are pressed together aggregates are destroyed which reduces pore space
What is absorbed water (hydroscopic water)
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
What is capillary water and gravitational water
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
What is field capacity and permanent wilting point
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
What is Available water capacity
Field capacity - permanent wilting point
What does soil colour indicate
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
What is soil temperature
The rate of chemical reaction doubles with every 10*C rise in temperature so the warmer the soil the faster the growth rate
What is soil erosion
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
What is carbon sequestration
The removal of carbon dioxide from the atmosphere by plant photosynthesis and storing as plant biomass and organic soil matter
What are the five types of mineral particles found in soil
Gravel
Coarse sand
Fine sand
Silt and clay
Minerals matter
Gravel and sand lead to good drainage and aeration
Silt and clay are good for water retention and clay and has high fertility levels
Factors that affected structural development
Freezing and thawing Soil organic matter Animal activity Wetting and drying Plant root activity Cultivation and tillage
