Soils

Question 1

Alluvial

Answer 1

Transported from original source via rivers and deposited further downstream

Consist of silt, sand, clay, gravel and large amounts of organic matter - very fertile soils.

Question 2

Loess

Answer 2

Deposited large distances from their origin by the action of wind.

Tends to be light and fine and prone to erosion.

Primarily made up of fine sand and silt - generally quite fertile.

Question 3

Sedentary

Answer 3

Have not been transported, formed from the parent rock directly beneath them.

Question 4

Factors affection soil formation

Parent material

Answer 4

Parent material - rate of soil accumulation is dependent upon physical properties, pH and structure of underlying rocks.

Question 5

Factors affection soil formation

Climate

Answer 5

Warm temperatures lead to more rapid decomposition, along with moisture provided from precipitation.

Question 6

Factors affection soil formation

Biota (organisms)

Answer 6

Presence of flora leads to an accumulation of leaf litter - becomes humus layer after being broken down by activities of detritivores.

Question 7

Factors affection soil formation

Topography

Answer 7

Weathering on exposed slopes removes any build up of soil but soil is accumulated where slope levels to flood plane.

Question 8

Factors affection soil formation

Time

Answer 8

Time is crucial to the formation of soil, it can take 50yrs to form 1mm of new soil.

Question 9

Soil profile and horizons.

Answer 9

When a vertical section is cut through a soil the result is a SOIL PROFILE.

The profile is divided into a series of HORIZONS, these run roughly parallel to the surface of the soil.

Soil horizons are relatively uniform and physically/chemically/ and/or bio locally distinct form the layer above and below.

Question 10

O horizon

LGH layers

Answer 10

O- Organic material at the surface - living organic matter and leaf litter.

L - slightly comminuted litter
F - Fermented horizon
H - humidified layer

Question 11

A horizon

Answer 11

Commonly referred to as top soil.
Mixed organo-mineral composition.
Often darker than lower layer as it contain partially decomposed organic matter.
Majority of root growth occurs here.

Question 12

E horizon

Answer 12

Horizon where maximum leaching occurs (eluviation)
Minerals are washed down causing a layer of resistant minerals.
Most common in forested areas.

Question 13

B horizon

Answer 13

Commonly referred to as subsoil.
High levels of minerals washed down from higher horizons.
Anoxic and greyer in colour.

Question 14

C horizon & R horizon

Answer 14

Soil from parent material, weathered but otherwise not altered by pedogenesis.

R horizon is bedrock which has not been weathered.

Question 15

Iron pan podzol

Answer 15

Infertile soils.
Formed beneath dense coniferous forests and Ericacaceous shrubs.
acid pH 3.0-6.5
Parent material often sand and gravel.
Limited organisms eg earthworms because of acidity. - this results in a layer of partially decomposed leaves in surface called mor.
Nutrients leach from A horizon.
Leaching from A horizon results in an iron pan just below, it is rusty brown in colour, has strong cohesion. Can be impenetrable barrier.
Layer below iron pan can be reasonably fertile.
Nutrient cycling is very slow under these conditions.
Very difficult to cultivate.

Question 16

Brown Earth

Answer 16

Slightly acidic. ( pH4.5 to 8.0).
High fertility.
Formed under densely forested areas of native deciduous trees with herbaceous undergrowth - leaf litter, deposited on surface has been incorporated into the soil by fauna.
Occurs in areas of reasonable rainfall.
A horizon is rich in organic matter and organisms.
A & B horizons are dark brown in colour.

Under these conditions nutrient cycling is rapid - very productive land

Question 17

Redzina

Answer 17

Shallow calcerous soil.
Derived from limestone and chalk parent rock.
pH generally greater than 8.0.
Soils remain shallow, sites often on incline.
Free draining, doesn’t retain water for long.
No B horizon, large weathered chunks of parent rock are present.
Plant growth limited to calcicoles.

Question 18

Gleys

Answer 18

Greyed brown earths display some degree of water logging at depth.
Groundwater gley occur at depth due to high water table
Groundwater gley are formed where impermeable subsoil is present., often in association with large bodies of water.

Clay particles leaching from B horizon can cause a clay pan.
Cultivation at the wrong time or always to the same depth can cause a plough pan. Water cannot infiltrate down and a surface-water gley develops.
Surface water gleys present typical blue grey colouration immediately above pan in surface layers if soil.
Rain or irrigation water drain very slowly.

Question 19

Problems with planting in gley soil.

Answer 19

Poor root activity - poor aeration/structure/AFP
Death of roots - anabolic aeration, alcohols produced.
Low levels of nutrients resulting in foliage problems.
Early wilting - indicative of root problems.

Question 20

Improving gley soils

Answer 20

Drainage.

Breaking up of soil pans

Question 21

Crumb

Answer 21

Very fine structure, characteristic of surface soils.
Units near spherical or ovoid but irregular faces.
Found on cultivated land, weathered sites or woodland.
Light soil, very conductive air and water content.
Fine filth is particularly important for germination of seedlings.

Question 22

Prismatic

Answer 22

Sometimes referred to as columnar.
Vertical prismatic structures.
Mainly found in B horizons which contain large amounts of clay.
Most common in soils of arid and semi-arid regions.
Good drainage and root penetration.

Question 23

Blocky

Answer 23

Associated with heavier clays dnd soils which have low organic matter content.
Mostly found in B horizons, sometimes in surface horizon.
Development of blocky structures is due to expansion and contraction of the clay component in soil by freezing and thawing, wetting and drying.

In B horizons they promote good drainage, aeration and root penetration.

Question 24

Platey

Answer 24

Associated with areas of compaction eg plough pans or heavy leaching, commonly in the E horizon.
Units are flat, plate like.
Associated with poor drainage.
Horizontal orientation of the structure tends to hinder the penetration of roots.

Question 25

Massive (amorphous)

Answer 25

Large units which require moderate pressure to break them up.
Common in disturbed clay soils.
No real arrangement of the unit.

Question 26

Cation

Answer 26

A cation is a positively charge atom or molecule.
Give + symbol.

Eg
Single element - Hydrogen (H+)
Compound element - Ammonium (NH4+)

Question 27

Anion

Answer 27

Negatively charged atom or molecule.
Given symbol of -
Eg
Single element - Chlorine (Cl-)
Compound element - Nitrate (NO3-)

Question 28

Cation exchange

Answer 28

Way in which nutrients can be held and stored in soil and made available for uptake by plants (absorption).

Negative surfaces can attract and hold positively charged cations.

Cations can be stored on negatively charged surfaces and they can be exchanged for other cations in the soil solution.

Cation Exchange Capacity measures the ability of the soil to store and release cations for plant uptake.

Question 29

Adsorption and absorption

Answer 29

Adsorption - refers to surface activity.

Absorption - being taken up inside.

Question 30

How soil texture affects CEC

Answer 30

CEC of soils increase as percentage of clay increases

Question 31

How pH affects CEC

Answer 31

When soil pH increases more H+ ions dissociate from the clay minerals, leaving a more negative charge.

Question 32

How soil humus content affects CEC

Answer 32

The higher the humus content, the higher the cation exchange will be.

Question 33

How type of clay present in soil affects CEC

Answer 33

CEC of a clay soil depends on which clay minerals are present as they all have different CEC.

Eg..
CEC of soil dominated by Vermiculite is much higher than Kaonite

Question 34

Buffering capacity of soil.

Answer 34

Buffering capacity - soils ability to withstand changes to pH.

Eg. To raise the pH if a soil more lime would be required in a soil with a high buffering capacity.

Clay and organic matter in soils raises CEC and buffering capacity of soil.

Question 35

Colloids

Answer 35

Colloids are very small soil particles, usually negatively charged.
They have large surface area onto which positively charged nutrient ions (cations) are adsorbed.

Question 36

Humus

Answer 36

Comprises fine fine material of organic origin after readily degrade able material has been broken down

Question 37

Positive effects of organic matter and humus on soils

Answer 37

Improvements in:
Soil structure
Particle aggregation
Water holding properties.
Soil matrix diversity.
Absorption and chemical holding of certain pollutants.
Adsorption and retention of soil nutrient ions.
Cycling of plant nutrient ions.
Buffering capacity.

Question 38

Humification

Answer 38

i) breakdown of carbohydrates and sugars by detritivors tha feed in dead plant and animal matter.
ii) Cellulose, lignin decompose more slowly.
iii) Organic acids, proteins and starches decompose quickly.
iv) Fats, was and some resins are relatively stable.
v) Lignin is an important humus builder, transmuted by activities of white rot fungus associated with animal and microbial activity.

Residues of these processes are HUMUS.