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

Question 16

soil structure

Answer 16

structure refers to how the various particles of sand, silt, and clay fit together, creating pore spaces of various sizes

Question 17

aggregates

Answer 17

chemical and biological processes that glue sand, silt, and clay particles together

soil microorganisms including mycorrhizae, earthworms, and plant roots help created aggregates

Question 18

granular structure

Answer 18

common in the upper layer of undisturbed native soils, rapid drainage

Question 19

block structure

Answer 19

common in the lower layers undisturbed native soils, rapid to moderate drainage

Question 20

platy structure

Answer 20

common in soils high in clay, slow to no drainage

Question 21

peds

Answer 21

describes the soil’s individual aggregates or clods

Question 22

pore space

Answer 22

controls soil drainage characteristics

Question 23

large pores

Answer 23

water moves rapidly down through the soil profile, common in sandy soils

pose environmental hazards due to rapid leaching

Question 24

small pores

Answer 24

water is slow to move or may not move at all, common in compacted soil and soils with greater than 20% clay content

easily waterlog

Question 25

soil pH

Answer 25

a measurement of the acidity or alkalinity of a soil

7.0 is neutral, below 7.0 is acidic, and above 7.0 is basic or alkaline. a pH range of 6.8 to 7.2 is near neutral

Question 26

soil amendment

Answer 26

any material mixed into a soil

Question 27

humus

Answer 27

the stable end products of decay, it can take decades to decompose and is very dark in color

humus improves soil suitability for beneficial organisms and plants

Question 28

improve water- and nutrient- holding capacity in sandy, gravelly, and decomposed granite soils

Answer 28

select well-decomposed materials like finished compost, aged manure, and peat

Question 29

improve aeration and infiltration (improve structure in clayey soils)

Answer 29

select fibrous materials like composted wood chips, peat, and straw

Question 30

mulch

Answer 30

any material placed on the soil surface

Question 31

plant nutrition

Answer 31

the need for basic chemical elements for plant growth (17 elements needed for normal growth)

Question 32

fertilization

Answer 32

the application of plant nutrients to supplement the nutrients naturally occurring in the soil

Question 33

primary nutrients derived from water and air

Answer 33

carbon, hydrogen, oxygen

Question 34

primary nutrients derived from soil

Answer 34

nitrogen, phosphorus, potassium