Unit 5.1: Introduction to Soil Systems

Question 1

What is soil?

Answer 1

Material composed of five ingredients: minerals, organic
matter, living organisms, gas, and water.

Question 1

Importance of soil

Answer 1

• food consumed depends upon soil
• plants grow in soil (hold water and mineral nutrients)
• habitat for many organisms
• act as enormous filter for any water that passes through it, altering chemistry of that water (modify the chemical composition by absorbing excess nutrients, such as nitrogen and phosphorus, from agricultural runoff or wastewater)
• store and transfer heat,
  eg. moderate temperature fluctuations between day and night. This thermal inertia is important for creating a more stable environment for plants, animals, and humans
  eg2. proper management of soil can enhance its ability to act as a carbon sink

Question 2

The soil system

Answer 2

dynamic ecosystem that has inputs, outputs, storages and flows

storages: organic matter, organisms, nutrients, minerals, air and water

inputs: organic and inorganic matter from precipitation and energy

outputs: uptake by plants and soil erosion

transfers: biological mixing, translocation and leaching

transformations: decomposition, weathering (breaking down rocks naturally) and nutrient cycling

Question 3

Soil profile

Answer 3

vertical cross-section of the soil, made of layers running parallel to the surface.These layers are known as soil horizons.

Question 4

Leaching

Answer 4

Natural process by which water-soluble substances such as
calcium are washed out from soil.
- may reduce the fertility of a soil.
- may occur due to rain or irrigation
- fertilizers and chemicals also get washed away with water and reach water bodies causing water pollution

Question 5

The soil texture triangle

Answer 5

Mineral portion of soil can be divided up into three particles based on size: sand, silt and clay.

Most consist of mixture of soil particles depends on relative proportion of sand, silt and clay particles

Question 6

Sandy soils

Answer 6

grainy and fall apart easily

Particle diameter:
0.05 - 2 mm

Question 7

Silty soils

Answer 7

slippery and holds together better than sandy soils

Particle diameter:
0.002 mm - 0.05 mm

Question 8

Clay soils

Answer 8

sticky and can be rolled up
into a ball easily

Particle diameter:
< 0.002 mm

Question 9

Minerals

Answer 9

These are derived from the weathering of rocks and include sand, silt, and clay. The proportions of these particles determine the soil’s texture.