Importance of soil

Question 1

Soil functions

Answer 1

• medium for growth
• recycling system for nutrients and organic waste
• habitat for soil organisms
• system for water supple and purification
• engineering medium

Question 2

Basic requirements for crop growth

Answer 2

• anchorage
• water
• air, particularly oxygen
• nutrients
• insulation
• phytotoxin control

Question 3

Soil management

Answer 3

• cultivation
• drainage
• irrigation
• nutrient input
• organic matter

Question 4

Long term soil quality

Answer 4

• acidification
• salinity
• erosion
• compaction
• waterlogging
• desertification
• chemical pollution

Question 5

Water and air pollution

Answer 5

• nitrate, ammonia
• phosphorus
• pesticides
• heavy metals
• radionuclides
• erosion
• surface runoff

Question 6

What are soils made from?

Answer 6

PORE SPACE
- 20-30% air
- 20-30% water
SOIL SOLIDS
- 45% mineral
- 5% organic

Question 7

Physical weathering

Answer 7

• thermal, due to differential rates of mineral and rock expansion
• mechanical, due to freeze-thaw and plant root effects, and to differential rates of mineral expansion when exposed to water

Question 8

Chemical weathering

Answer 8

• hydrolysis (attack inter-mineral bonds and alter mineral compostion)
• carbonation (accelerated hydrolysis)
• hydration (absorption of water)
• dissolution (minerals dissolve in water)
• oxidation and reduction (minerals weaken through a change in their oxidation state)

Question 9

Physical weathering

Answer 9

• thermal, due to differential rates of mineral and rock expansion
• mechanical, due to freeze-thaw and plant root effects, and to differential rates of mineral expansion when exposed to water

Question 10

Main organic inputs

Answer 10

• cellulose
• lignin
• fats and waxes
• sugars and starches
• protein
• hemicellulose

Question 11

Plant and animal remains

Answer 11

Soils vary in the content and age of their organic matter

- days, weeks and months ~(residues) to centuries (humus) old

Question 12

Transformation of organic inputs

Answer 12

• organic residues are slowly altered by micro-organisms to new material called hums, which is both chemically and physically different from the chemicals that make up plant and animal remains
• organic residues persist in soil fro a few years whilst humus is very stable an can be >1000 years old
• humus is intimately mixed with the mineral fraction and imparts a dark brown colour to soil

Question 13

Soil horizons definition

Answer 13

the movement and accumulation of mineral and organic materials down through soil as it develops produces a number of distinct layers

• some materials are lost from the soil, determined largely by rate of water movement
• some parts of the profile become enriched, other become depleted of certain minerals

Question 14

soil horizons

Answer 14

O- plant and animal residues & decomposing organic matter
A - mixture of mineral and humified organic matter
E - eluvial zone, soil is depleted from soluble and insoluble material by leaching
B - illuviation, zone of accumulation
C - parent material