Introduction to soil systems

Question 1

Name 6 functions of soil

Answer 1

• All food we consume depends on soil
• Soil is a habitat for many organisms
• Holding water + mineral nutrients that plants depend upon
• Act as filter for water passing though, altering its chemistry
• Store + transfer heat so affecting atmospheric temperature
• Part of lithosphere where life processes + soil forming processes take place

Question 2

Soils are made up of 4 main components:

Answer 2

• Mineral particles from underlying rock
• Organic remains from flora+fauna
• Water within spaces between soil grains
• Air also within soil grains

Question 3

What is the function of rock particles and soil?

Answer 3

• provides skeleton of soil

- derived from underlying rock

Question 4

How is humus formed?

Answer 4

Plant + animal matter in the process of decomposition

Question 5

What is the function of humus?

Answer 5

• gives soil a dark colour
• as it breaks down, it returns mineral nutrients back to soil
• absorbs + holds on to large amount of water

Question 6

What is the function of water in soil?

Answer 6

• dissolved mineral salts move through soil + so become available to plants
• rapid downward movement of water causes leaching of minerals
• rapid upward movement cause salinisation
• large volumes of water in soil lead to anoxic conditions + acidification

Question 7

What are the two gases present in soil?

Answer 7

Mainly oxygen + nitrogen

Question 8

What is the function of air in soil?

Answer 8

Well-aerated soils provide oxygen for the respiration of soil organisms + plant roots

Question 9

What is the function of soil organisms?

Answer 9

• large particles of dead organic matter are broken down by worms
• smaller particles are decomposed by soil microorganisms thus recycling mineral nutrients
• larger burrowing animals (eg moles) help mix + aerate soil

Question 10

What is translocation?

Answer 10

Materials are sorted and layers are formed by water carrying particles either up or down, known as translocation

Question 11

What is the O Horizon (Top Layer)

Answer 11

• uppermost layer of newly added organic material
• comes from organisms that die + end up on top of the soil
• fungi, bacteria will start to decompose dead material

Question 12

What is the A Horizon (Layer 2)

Answer 12

• this is where humus builds up
• humus forms from partially decomposed organic matter
• often decomposition is incomplete + a layer of dark brown organic material is formed (the humus layer)
• in normal conditions, organic matter decomposes quickly through decomposer food web + minerals released for plants
• waterlogging reduces no. soil organisms resulting in build-up of organic matter + formation of peat soils

Question 13

What is the B Horizon (Layer 3)

Answer 13

soluble minerals + organic matter tends to be deposited from layer above

Question 14

What is the C Horizon (Layer 4)

Answer 14

mainly weathered rock from which the soil forms

Question 15

What is the R Horizon (Layer 5)

Answer 15

Parent material (e.g. bedrock)

Question 16

How big is a clay particle?

Answer 16

< 0.002mm

Question 17

How big is a silt particle ?

Answer 17

0.002 - 0.05 mm

Question 18

How big is a sand particle?

Answer 18

0.05 - 2mm

Question 19

What is a loam soil?

Answer 19

Ideally 40% sand, 40% silt, 20% clay

Question 20

Why are loam soils ideal for agriculture?

Answer 20

• sand particles ensure good drainage + good air supply to the roots
• clay retains water + supplies nutrients
• silt particles help to hold the sand + clay particles together + can be worked easily

Question 21

What is the porosity of soil?

Answer 21

The amount of space between particles

Question 22

What is soil permeability?

Answer 22

The ease at which gases and liquids can pass through the soil

Question 23

Advantages and disadvantages of sand and clay soils

Answer 23

• CLAY | low permeability means it can lock dissolved minerals between pores making it hard for plant roots to access. Result = soil rich in minerals but low fertility
• Also encourage high acidity leading to leaching of important nutrients e.g. potassium and magnesium
• SAND | sand particles ensure good drainage and a good air supply to the roots

Question 24

How has the acidification of soils had a major impact on forestry in Northern Europe?

Answer 24

• Acid rain caused by industrial pollution has made the soil more acid
• This has meant more available aluminium + iron ions in the soil causing damage to evergreen forestry through needle death

Question 25

Is fertile soil a renewable resource?

Answer 25

Fertile soil is a non-renewable resource // once it is lost, it cannot be replaced quickly

Question 26

Fertile soil has enough nutrients for healthy plant growth. What are these and how do human activities inadvertently remove them?

Answer 26

• main nutrients = nitrates, phosphates, potassium
• these nutrients leached out of soil // removed when a crop is harvested
• they have to be replaced via chemical fertiliser, growing legumes, crop rotation or through application of manure, compost…