Lesson 1: Introduction to Soils

Question 1

soil

Answer 1

“the unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.”

Question 2

unconsolidated materials

Answer 2

loose materials composed of multiple units (e.g., sand, gravel, etc.) unlike hard, massive materials like rock

Question 3

soil composition (well-managed)

Answer 3

usually around 50% percent of the soil’s volume is composed of solid particles (i.e. decomposed rocks or sediments), with 1-5% being organic matter

the other 50% is empty space, i.e. “pores” (25% water, 25% air)

Question 4

organic matter

Answer 4

the live organisms in the soil, and plant, animal, and microbial residues in various stages of decomposition

Question 5

five soil-forming factors

Answer 5

factors that cause variation in soils in different locations

1. Parent material (i.e. starting material for a soil)
2. Climate (precipitation, temperature, wind)
3. Topography
4. Biological organisms
5. Time

Question 6

horizons

Answer 6

In naturally formed soils, distinct layers develop. They may blend together gradually or have abrupt borders between layers, and are identified by letter codes.

Question 7

A horizon

Answer 7

“topsoil”

The A horizon is usually the surface horizon. This is an area of high biological activity with the greatest organic matter content. It is also a zone of leaching. Most plant roots are found in the A horizon.

Question 8

B horizon

Answer 8

“subsoil”

This layer usually contains less organic matter than the surface layer but accumulates the dissolved materials leached from the A horizon (clays, iron oxides, aluminum, and dissolved organic compounds). For this reason, the B horizon typically contains more clay than the surface layer.

Question 9

C horizon

Answer 9

The C horizon contains unconsolidated material that has been minimally affected by the soil forming factors, and may or may not be the same as the parent material from which the soil formed.

Question 10

landscape soils

Answer 10

“urban” soils

soils that are found in a typical neighborhood community around homes, parks, schools, offices, parking lots, and buildings

In compacted landscape soils, the horizons are scrambled and not defined, organic content is low, and air and water movement is reduced.

Question 11

texture

Answer 11

the size of the particles that make up the soil (e.g., sand, silt, clay)

Question 12

sand

Answer 12

the largest particle size and feels gritty

Question 13

silt

Answer 13

moderate in size with a smooth or floury texture

Question 14

clay

Answer 14

the smallest sized particle and feels sticky

Question 15

loam

Answer 15

a soil with a combination of sand, silt, and clay sized particles