Lecture 8 CM

Question 1

Soil is created by the interaction of

Answer 1

physical and chemical
weathering of rock; sedimentation; climate and living organisms

Question 2

Overall soil fertility is influenced by

Answer 2

physical, chemical and biological components

Question 3

Soil nutrient cycling and availability are controlled by

Answer 3

bacteria, which are influenced by soil pH, aeration, temperature and nutrient balance

Question 4

After climate, soil fertility is

Answer 4

the most important factor in controlling ecosystem NPP, and in determining the sustainability of local agricultural systems

Question 5

After temperature and rainfall, ___ has greatest impact on Biome structure

Answer 5

Soil

Question 6

Important aspects of soils that determine biome and habitat productivity:

Answer 6

Physical component

• Inorganic component

Organic component

Question 7

Physical component

Answer 7

Physical component
(f. of structural and chemical properties, water, temperature)

Question 8

• Inorganic component

Answer 8

• Inorganic component
(f. bedrock, weathering and siltation)

Question 9

• Organic component

Answer 9

• Organic component
(f. OM, soil microbes, protists, fungi, animals, plants)

Question 10

The productivity of a given over-ground habitat is dependent on the

Answer 10

functioning and efficiency of the organic component of the soil, particularly the microbes

Question 11

The soil is a very complex,

Answer 11

The soil is a very complex, 3-dimensional ecosystem with highly diverse microbial and invertebrate communities

Question 12

biological activity and nutrient cycling is concentrated in

Answer 12

the uppermost layer

Question 13

Soil Profile: horizons, biota & nutrient cycling

Answer 13

Humus - Decaying Organic Matter [OM] Topsoil - Humus OM/ mineral/ clay mix Leached layer - sand and silt
Subsoil - clay + leached minerals Regolith - bedrock, rocks + some clay

Question 14

A Typical Soil Profile

Answer 14

OM
Humus/ Topsoil
Leached layer, low mineral content
Subsoil rich in oxidised-metals that have been leached from above

Question 15

In general, soil profile is consistent across different habitat types, with

Answer 15

nutrients and microbes bound up with organic matter in the upper layers, and nutrient-poor leached layers underneath

Question 16

Soils develop over time in conjunction with

Answer 16

bedrock weathering and biological activity

Question 17

In each habitat, soil develops over time as

Answer 17

bedrock weathers and biological activity increases

Question 18

Most often, soil forms around

Answer 18

fragments of the bedrock directly below, other times, glacial or river sediment dominates

Question 19

The amount of soil biological activity is influenced by

Answer 19

abiotic factors and the soil biota

Question 20

A mix of organic and inorganic components determine

Answer 20

the fertility of soils

Question 21

• Inorganic component:

Answer 21

alumina-silicates (containing Mg, K, Na, Fe, Ca etc. in compounds); silica; calcium carbonate

Question 22

• Organic component:

Answer 22

: raw decomposing material; colloidal humus

Question 23

Soils comprise a continuum of organic types, ranging from

Answer 23

from the most fertile
(called ‘Mull’) to the least fertile (called ‘Mor’)

Question 24

Mull organic matter:

Answer 24

• characteristic of fertile soils
• good aeration and temperature
• cycling of organic material is rapid
• microbes and soil animals abundant

Question 25

Mor organic matter:

Answer 25

• forms in less favourable condition (base-poor rocks or in waterlogged soils) - OM accumulates and acidifies (leaching)
• few decomposers, no nitrifying bacteria

Question 26

Soil drainage characteristics vary according sediment composition

Answer 26

Poor drainage can alter soil chemistry by increasing waterlogging, decreasing aeration and pH.

Question 27

Soils with good drainage have the

Answer 27

capacity to be well-aerated, with neutral to alkaline pH [depending on bedrock geology and type of sediment]

Question 28

The most fertile soils are generally those with

Answer 28

good drainage, over base-rich bedrock

Question 29

In Ireland these factors commonly

Answer 29

overlap in the East and Southeast

Question 30

Soil pH has a major impact on soil fertility and ecosystem biodiversity

Answer 30

Nutrient availability decreases with increasing soil acidity (lower pH)
• This directly impacts the ability of plants to source essential nutrients for growth and reproduction
• The impact of soil acidity can be seen in the Arctic Tundra of Alaska, for example, where fewer Plant Species survive in low pH soils compared to neutral soils (after Gough et al, 2000)

Question 31

The Soil Biota comprises several different groups of organisms:

Answer 31

Bacteria, fungi and earthworms have greatest impact on soil health
See slide

Question 32

Soil Bacteria

Answer 32

Pseudomonas (free-living and rhizophilous Bacteria)

Actinomycetes (Filamentous Bacteria)

Nitrifying bacteria (oxidise ammonia to nitrite and nitrate)

Question 33

Soil Fungi

Answer 33

Fungi - root mycorrhizae (symbionts)

Fungi -opportunistic saprotrophs

Question 34

Soil Protozoa

Answer 34

Motile protists (bacteria eaters), eg. Amoebae, Flagellates, Ciliata

Question 35

Soil Invertebrates – soft bodied

Answer 35

Nematodes (herbivores, detrivores and predators)

Earthworms (detrivores e.g. Lumbricus terrestris)

Question 36

Soil Invertebrates – exoskeleton

Answer 36

Beetle (Coleoptera) and Fly (Diptera) Larvae, can be detrivores, omnivores or carnivores

Collembola or Springtails (Detrivores) Along with earthworms & nematodes are the most numerous invertebrates

Woodlice (Crustacea) Detrivores

Question 37

The breakdown of soil organic matter involves many organisms

Answer 37

See slide

Question 38

Decomposition and nutrient cycling in soils are impacted by both temperature and water content

Answer 38

Relative soil microbial respiration rate, a measure of the overall biological activity of the soil, is significantly impacted by water content and temperature.