Soil Physical Properties

Question 1

What is soil physics?

Answer 1

It is the understanding of how solids, water, and air in the soil interact with each other.

Question 2

Why do we care about the physics of the soil?

Answer 2

To ensure the continuity of the ecosystem services the soil lends to us. (Provision, regulatory, cultural support, etc.)

Question 3

What is soil matrix?

Answer 3

They are the solid particles in the soil that give it structure. This includes the parent material and the organic matter.

Question 4

Why is the soil matrix important?

Answer 4

It determines the geometric characteristics of the pores in which water and air are transmitted and retained.

Question 5

What are 6 examples of soil characteristics derived from color?

Answer 5

1. Identify soil classification
2. Distinguish soil horizons
3. Waterlogging conditions
4. Drainage class
5. Warm reddish color: Tropical and subtropical zones
6. Black and grey: Temperate zones

Question 6

What is the biggest particle that is considered soil?

Answer 6

2mm

Question 7

What are 3 factors that influence soil color?

Answer 7

1. Organic Matter
2. Water content
3. Presence and oxidation states of iron and manganese

Question 8

What are the 5 principal hues in soil?

Answer 8

Red, Yellow, Green, Blue, and Purple.

Question 9

What are the three soil color characteristics using the Munsell Soil Color chart?

Answer 9

1. Hue (Basic color)
2. Chrome (brightness)
3. Value (Shade)

Question 10

What does 0 and 10 value mean?

Answer 10

0 = Black
10 = White

Question 11

What is the most used property to characterize the solid phase of the soil?

Answer 11

Soil Texture

Question 12

How can you measure soil texture qualitatively vs. Quantitatively?

Answer 12

Qualitatively: Through the feel of soil
Quantitatively: Measuring the ratio of different sized particles.

Question 13

What is the range in particle size of sand?

Answer 13

2mm - 0.05mm

Question 14

What is the range in particle size of silt?

Answer 14

0.05mm - 0.002mm

Question 15

What is the range in particle size of clay?

Answer 15

0.002mm - 0.0002mm

Question 16

What are the two methods of determining soil texture in the lab?

Answer 16

1. Dispersion of the soil sample in an aqueous solution to separate the primary particles.
2. Separation of the particles into size groups.

Question 17

What are the three limitations to Stokes Law?

Answer 17

1. Not all particles are spherical
2. The soil particle mass is average and some particles can be heavier or lighter.
3. Increasing temp decreases density and viscosity of water.

Question 18

Briefly explain the Pipetting method.

Answer 18

For this method, you pipet different samples from a beaker of soil and water solution. Pipet solutions at different time intervals and different heights to reveal particle size.

Question 19

Briefly explain hydrometer method.

Answer 19

A hydrometer is used to measure relative density. The test tube with more water separated is less dense.

Question 20

What is the deflocculation process?

Answer 20

It is the process of separating soil particles.

Question 21

Why do clay soils need to dry for a much longer period of time?

Answer 21

Because they retain water very well.

Question 22

What are the 6 stoke’s law assumptions?

Answer 22

1. The particles are small enough to be unaffected by the random movement of water molecules.
2. The particles are rigid, spherical and smooth
3. The particles have the same density
4. The suspension is sufficiently dilute and dispersed that particles do not interfere with one another and each settles independently.
5. Fluid flows around the particles in laminar not turbulent.
6. Fluid density and viscosity are constant during the settling period.

Question 23

Briefly describe single grained soil structure.

Answer 23

Soil particles are not attached at all. Ex: Dessert sand

Question 24

Briefly describe massive soil structure.

Answer 24

Soil particles are tightly packed.
Ex: Dry Clay.

Question 25

Briefly describe aggregate soil structure.

Answer 25

Soils that are ideal for farming. Particles are associated with small clots known as aggregates or peds.