Exam Study Flashcards
Why is the soil important for ecological functions?
- Provides biomass production
- Provides a reactor
- Acts as a biological habitat and genetic reserve
Why is the soil important for human functions?
- Acts as a physical medium, serving as a base for structures
- Source of raw material supply
- Part of our cultural heritage (archaeology)
What do plants require from the soil?
- Support
- Oxygen
- Water
- Nutrients
What is aeration?
Aeration is the process by which oxygen enters the soil and CO2 and other gases escape.
What is soil fertility?
The physical fertility + the chemical fertility + the biological fertility. Also known as the fitness for use.
What is a soil?
The collection of natural bodies on the earth’s surface, containing living matter and capable of supporting plants.
What is soil texture?
Soil texture is the particle size distribution of the solid inorganic or mineral part of the soil i.e the proportion of sand, silt and clay within the soil.
How is a soil given a textural name?
According to the relative amounts of sand, silt and clay, and the physical location of the soil.
What are the two methods for soil texture analysis?
Mechanical analysis (in a lab) and estimation by feel.
What soil properties does texture affect?
- Water movement
- Aeration
- Water retention
- Nutrient availability
- Ease of tillage
- Susceptibility to compaction
- Erosion
How does a soils texture affect aeration?
Fine textured soils are often poorly drained and have poor aeration, where as coarse textured soils have better natural drainage and aeration.
How does a soils texture affect water movement?
Water tends to move much more quickly through coarse textured soils than it does through fine textured soils.
How does a soils texture affect nutrient availability?
Sandy soils often have relatively small reserves of key plant nutrients.
How does a soils texture affect ease of tillage?
Clay soils are often difficult to cultivate.
How does a soils texture affect susceptibility to compaction?
Intermediate and fine textured soils are prone to soil compaction.
How does a soils texture affect erosion?
Soil particles that do not cohere well are at risk to erosion by both wind and water.
What are attributes that are associated with texture?
Surface area, charge and shape.
What is soil structure?
The arrangement and organisation of soil particles into aggregates (or peds) and the stability of such arrangement to stress.
How is soil structure assessed in the field?
- Degree of development
- Shape
- Size of peds
What is good soil structure?
- Smaller aggregates
- Stable aggregates
How is structure formed in soils?
- Wetting and drying cycles
- Freezing and thawing cycles
- Roots
- Soil Organisms
- Roots
- Organic Matter
- Iron and aluminium oxides
- Clay particles
- Soil Tillage
What soil properties does structure affect?
- The rate of water entry and movement
- Water storage and retention
- Aeration
- Root penetration
- Erosion
- Productive potential of the soil
Name some management practices that help with soil structure.
- Cultivating and harvesting at the correct water content.
- Don’t over cultivate
- Use minimum tillage/direct drilling
- Grow perennial pastures in crop rotation
- Add compost to the soil
- Add lime if required to increase pH
- Avoid heavy traffic and stock when soils are wet
What is porosity?
Porosity is the fraction of soil volume that consists of holes or voids.
What are the three important characteristics of the pore space?
- The total volume of pores
- The size distribution of pores
- The continuity of pores
What is a micropore?
A smaller pore, smaller than 30um in diameter.
What is a micropore?
A larger pore, bigger than 300um in diameter.
What do the larger pores provide?
Aeration and drainage.
What do the smaller pores provide?
Holds water.
What is bulk density?
The density of an oven dried soil sample.
What is gravimetric water content?
The mass of water relative to the mass of oven-dry soil.
What is volumetric water content?
Volume of water relative to the total soil.
What is the soil moisture content important for?
- Determining irrigation requirements, assisting irrigation management
- Measuring the effectiveness of drainage systems
- Identifying the best timing and method of cultivation
