4.3 - Soil Composition and Properties

Question 1

Geological (rock) section of soil is made up of what 3 particles (in order from biggest to smallest)

Answer 1

1. Sand
2. Silt
3. Clay

Question 2

What is soil texture?

Answer 2

• Percent of sand, silt, and clay in soil
  - Always adds up to 100%

Question 3

What is caused because sand is bigger?

Answer 3

• It has more pores (empty spaces between particles)
  - This allows air and water to enter sandy soil easily
  - Clay has smaller pores, so it is harder for air and water to enter clay-heavy soils.

Question 4

What is porosity?

Answer 4

• The amount of pore space a soil has
  - more sand in soil = more porous/higher porosity (easier for water and air to enter)
  - more clay in soil = les porous/less porosity (harder for water and air to enter)

Question 5

Explain the soil texture chart

Answer 5

• soil texture is determined by clay, silt, and sand %
• tips for using soil texture chart
  - always start on bottom with sand %
  - move out to point where sand and silt meet
  - then go straight over to clay
  - make sure it adds up to 100%

Question 6

What is permeability?

Answer 6

How easily water drains through soil

Question 7

What happens with higher porosity?

Answer 7

Higher permeability

Question 8

What type of relationship is porosity and permeability?

Answer 8

A positive relationship

Question 9

What is H2O holding capacity?

Answer 9

• How well water is retained, or held by a soil
  - more porous/permeable = lower H2O holding capacity
  - Inverse relationship between porosity/permeability and H2O holding capacity

Question 10

What is porous, permeability, and H2O holding capacity’s effect on soil permeability

Answer 10

• Soil is too sandy (too permeable) drains water too quickly for roots and dries out
• Clay-heavy soil doesn’t let H2O drain to roots or waterlogs (suffocating them)
• Ideal soil for most plant growth in loam, which balances porosity or drainage, with H2O holding cap

Question 11

What is soil fertility?

Answer 11

The ability to support plant growth

Question 12

What are the nutrients for soil

Answer 12

1. N
2. P
3. K+
4. Mg2+
5. Ca+
6. Na+

Question 13

Factors that increase nutrients in soil

Answer 13

1. Organic matter (releases nutrients)
2. Humus (holds and releases nutrients) - also helps hold water so very important part of soil
3. Decomposer activity (recycles nut.)
4. Clay (neg. charge binds pos. nutrients)
5. Bases (Calcium carbonate - limestone)

Question 14

Factors that decrease soil nutrients in soil

Answer 14

1. Acids leach pos. charge nutrients
2. Excessive rain/irr. leeches nutrients
3. Excessive farming depletes nut.
4. Topsoil erosion

Question 15

Why is water needed for soil fertility?

Answer 15

it needs to hold water, but not too much

Question 16

What are factors that increase H2O holding cap of soil

Answer 16

• aerated soil (biological activity)
• Compost/humus/organic matter
• Clay content
• Root structure, especially natives

Question 17

What factors decrease the H2O holding cap in soil

Answer 17

• compacted soil (machines, cows, etc)
• topsoil erosion
• sand
• root loss

Question 18

Characteristics and tests of soil quantity (this is a lot)

Answer 18

1. Texture
   - Test: let soil settle in jar of water. Measure 3 layers that form (sand, silt, clay)
   - What it tells you: percent of sand, silt, and clay - how porous or permeable soil it is
2. Permeability
   - Test: Time for H2O to drain through column of soil
   - What it tells you: How easily water drains through soil. Too high, soil dries out. Too low, roots don’t get water or drown. Medium is optimal.
3. pH
   - Test: pH strip - H+ ion concentration
   - What it tells you: How acidic (low pH) or basic/alkaline (high pH) soil is. More acidic soil = less nutrient availability
4. Color
   - Test: Compare w/soil book color chart
   - What it tells you: The darker, the more humus, nutrients, and moisture
5. Nutrient Level
   - Test: Measure ammonium, nitrate, or phosphate lvl
   - What does it tell you: Higher nutrient levels = more plant growth. Low level could indicate acidic soil, deple