5.1 Introduction to Soil Systems

Question 1

Soil

Answer 1

composed of mineral and organic matter, air, and water, that forms the uppermost layer of the Earth’s surface and is capable of supporting plant life

Question 2

Soil texture

Answer 2

The relative proportions of sand, silt, and clay particles in soil.

Question 3

Clay

Answer 3

The smallest soil particles.

High porosity (holds water), but low permeability (slow to drain)

Question 4

Silt

Answer 4

Medium-sized soil particles (between clay and sand) that feel smooth and powdery.
Often river deposited.

Question 5

Sand

Answer 5

The largest soil particles, which feel gritty and allow for good drainage.

Question 6

Porosity

Answer 6

The measure of the void spaces in soil, affecting its ability to hold water and air.

Question 7

Permeability

Answer 7

Relates to drainage.
The ability of soil to transmit water and air through its pores.

Question 8

Horizons

Answer 8

The distinct layers of soil that form a soil profile.

Question 9

Soil profile

Answer 9

A vertical section (cross-section) of soil that shows all its horizons.

Question 10

“O” horizon

Answer 10

The topmost soil layer, rich in organic matter and decomposed material.

Humus lies above it, not within it.

Question 11

“A” horizon

Answer 11

The topsoil layer, rich in organic material and minerals, where most plant roots grow.

Question 12

“B” horizon

Answer 12

The subsoil layer, where minerals leached from above accumulate.

Question 13

“C” horizon

Answer 13

The layer of partially disintegrated and weathered parent material beneath the B horizon.

Question 14

Bedrock

Answer 14

The solid rock layer beneath the soil layers.
Sometimes called the “R” layer

Question 15

Parent material

Answer 15

The underlying geological material from which soil forms.

Question 16

Soil texture triangle

Answer 16

A diagram that classifies soil types based on the proportions of sand, silt, and clay.

Question 17

Loam

Answer 17

A balanced soil type with roughly equal parts of sand, silt, and clay, preferred by farmers for its fertility and workability.

Question 18

Soil texture preferred by farmers

Answer 18

Loam is preferred for its ideal balance of drainage, nutrient retention, and ease of cultivation.

Question 19

Physical soil surface crust

Answer 19

Protects soil from erosion and moisture loss but can inhibit seedling emergence.

Question 20

Biological soil surface crust

Answer 20

A community of living organisms on the soil surface (lichens, algae, mosses) that stabilizes soil and reduces erosion.

Question 21

Rainsplash erosion

Answer 21

The detachment and movement of soil particles caused by the impact of raindrops.

Question 22

Hoof action

Answer 22

the impact and movement of an animal’s hooves on the ground, which can influence soil compaction, aeration, and erosion

Question 23

Soil compaction

Answer 23

The compression of soil particles (often by grazing stock or vehicle tires) that reduces pore space, hindering root growth and water infiltration.

Question 24

Jar method

Answer 24

A technique to analyze soil texture by mixing soil with water in a jar, allowing particles to settle into layers of sand, silt, and clay.

Question 25

Why is soil important?

Answer 25

Soil is essential for plant growth, water filtration, carbon storage, and as a habitat for organisms.

Question 26

Soil ecosystem services

Answer 26

• nutrient cycling
• water filtration and storage
• carbon sequestration
• erosion management
• plant growth support

Question 27

Minerals in soil

Answer 27

Soil contains essential minerals like nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur needed for plant and animal life.

Question 28

Aggregate

Answer 28

A cluster of soil particles that bind together, creating pores for air and water movement.

Question 29

Bolus

Answer 29

A cohesive mass of soil formed by kneading and squeezing, used to assess soil texture by feel.

Question 30

Slaking

Answer 30

The breakdown of soil aggregates when exposed to water, indicating soil structure stability.

Question 31

Eluviation

Answer 31

involves the leaching of materials such as clay, iron, or organic matter from one horizon to another, usually from the upper horizons to the lower ones, leaving the upper horizons depleted of these substances.

Question 32

Topsoil vs subsoil

Answer 32

Topsoil: The uppermost soil layer, rich in organic matter and nutrients, essential for plant growth.

Subsoil: The layer beneath the topsoil, containing minerals leached from above but less organic matter.

Question 33

Alluviation

Answer 33

the process of deposition of sediment by flowing water, typically in the form of alluvium, which consists of materials such as silt, sand, clay, and gravel, often creating fertile land areas like riverbanks, floodplains, and deltas.

Question 34

Eluviation vs illuviation

Answer 34

eluviation involves the removal of materials from upper horizons, while illuviation involves the deposition of materials in lower horizons, both driven by the movement of water through the soil profile.

Question 35

Lithosphere vs pedosphere

Answer 35

the lithosphere is the rigid outer layer of the Earth’s crust and mantle involved in geological processes, the pedosphere is the layer of soil and living organisms that interact with the atmosphere and hydrosphere to support life on Earth

Question 36

Determining the moisture content of soil

Answer 36

measuring the weight difference of a soil sample before and after drying it in an oven to evaporate the water content.