Composition Of Soils

Question 1

What 3 components are soils made up of?

Answer 1

50% Solid
25% Liquid
25% Gas

Question 2

What do soil solids comprise of?

Answer 2

a. Inorganic materials

b. Organic materials

Question 3

What are inorganic materials in soil?

Answer 3

They contain no carbon
Residual minerals in rock
minerals formed as rock is broken down

Question 4

What are organic materials in soil?

Answer 4

They contain carbon
Humus residue resistant to microbal decomposition
Fresh and decomposing plant material and animal remains
Living macro (worms) micro (bacteria, fungi)

Question 5

What is meant by the liquid phase of soils what does it consist of?

Answer 5

Water which is held in the pores or holes in soil (like a sponge); and
contains dissolved materials including nutrients.

Question 6

What does the gas phase of soil contain?

Answer 6

Nitrogen gas (N2);
Oxygen (O2); and
Carbon dioxide (CO2) are present in generally similar concentrations to the atmosphere except that CO2 levels are normally higher in soil.

Question 7

What are the two terms of soil density?

Answer 7

a. Particle or absolute density

b. Bulk density

Question 8

What is meant by particle or absolute density of soil?

Answer 8

This is the density of the individual soil particles, that is, the ratio of the mass of the solids to the volume of solids.

Question 9

What is meant by bulk density of soil?

Answer 9

This is the ratio of the mass of solids to the total volume of soil, that is, solid plus pores.The higher the bulk density, the greater the weight of soil in a given volume, that is, the greater the compaction.

Question 10

What is meant by porosity off soil?

Answer 10

Total porosity is the proportion of the soil volume occupied by pores including those containing water and air.
The relationship between total porosity and bulk density is shown in the tablebelow (Total porosity decreases as bulk density increases).

Question 11

How can total porosity be calculated?

Answer 11

Total Porosity (%) = [1 - (bulk density / particle density)]x 100

Question 12

What is meant by pore size distribution?

Answer 12

Pore size between the soil particles can vary from large pores to small pores. These can be present in a soil at varying proportions as indicated in the figure below. Pore size distribution of a soil is more informative than the total porosity discussed above.