Soils Lecture 3- Marc

Question 1

in soil types, which stores the most Carbon?

Answer 1

permafrost
Soils contain estimated 1500-2400 PgC (P = peta = 1015)
Permafrost contains an additional ~1700 PgC
All vegetation 450-650 PgC
Oil reserves 173-264 PgC
Atmosphere contains ~730 PgC

Question 2

What services are provided by our soil?

Answer 2

Soils are nature’s recycling system, returning biomass and nutrients to forms that can be used by the next “generation” of life.
diversity, biomass, microorganisms. indirectly supports all life

Question 3

name some of the organisms which live in soil

Answer 3

nematodes
microbes
fungal hyphae
fungi
mites
springtails

Question 4

what is humus?

Answer 4

Humus is carbon that has resisted degradation

Question 5

characteristics of humus?

Answer 5

VERY slowly decomposed
Plant and microbial origin
Provides soil with its dark colour, especially in the A horizon

Question 6

what is the A horizon, when considering humus and soil

Answer 6

A horizon is the most biologically active layer, with higher organic matter and nutrients

Question 7

What is the exchange mechanism responsible for nutrient retention

Answer 7

Cation exchange

Question 8

what are Colloids?

Answer 8

Colloids are the smallest particles: of clay (mineral) or humus (organic) chemically active
Mainly negatively charged

Question 9

what would make a good soil?

Answer 9

one with High CEC = high nutrient
retention and good soil
fertility
Caiton Exchange Capacity

Question 10

which element is a Cation which can affect soil pH?

Answer 10

H+

Question 11

list things that will affect soil fertility

Answer 11

Nutrient abundance and balance (macro and micronutrients)
Bioavailable phosphorus often limiting
Type of clay; proportion of various sized particles (sand, silt)
pH (acidity, alkalinity)
Toxic elements
Salinity
Microbes

Question 12

how is soil fertility defined?

Answer 12

the ability to sustain plants

Question 13

define the following:
GEP:

ER:

NEP:

Answer 13

Gross ecosystem productivity (photosynthesis)
R: Ecosystem respiration
NEP: Net ecosystem productivity

Question 14

define GEP

Answer 14

Gross ecosystem productivity (photosynthesis)

Question 15

Define ER

Answer 15

ER: Ecosystem respiration

Question 16

define NEP

Answer 16

NEP: Net ecosystem productivity

Question 17

how are some of the ways forest soils fix carbon?

Answer 17

uptake and storage through photosynthesis and primary production minus decomposition/respiration
CO2 efflux through autotrophic respiration (leaf, shoot, and roots)
CO2 efflux through heterotrophic respiration (primarily from litter and SOM decomposition)

Question 18

how do forest soils lock in Methane and N2O

Answer 18

CH4 uptake by methane-oxidizing soil bacteria

N2O efflux through microbial nitrification and denitrification processes

Question 19

how do forest soils lock in Methane and N2O

Answer 19

CH4 uptake by methane-oxidizing soil bacteria

N2O efflux through microbial nitrification and denitrification processes

Question 20

how much carbon do peatlands hold globally

Answer 20

1/3

Question 21

how much carbon do peatlands hold globally

Answer 21

1/3

Question 22

what can a High water-table cause?

Answer 22

(when precipitation is ample) leads to anoxia, slow decomposition, but greater CH4 emissions

Question 23

why does Sphagnum peat decomposes slowly in bogs?

Answer 23

It is flooded, which makes it anoxic/anaerobic
It is acidic
It is nutrient poor

Question 24

what is peat subsidence?

Answer 24

irreversible lowering of the surface (subsidence) as a consequence of peat shrinkage and biological oxidation, with the latter resulting in a loss of carbon stock

Question 25

what is peat subsidence?

Answer 25

irreversible lowering of the surface (subsidence) as a consequence of peat shrinkage and biological oxidation, with the latter resulting in a loss of carbon stock

Question 26

how does pasture grazers affect soil degredation and erosion?

Answer 26

compaction due to hoof traffic often associated with over-grazing

Question 27

how does tillage and heavy equipment affect soil degredation and erosion?

Answer 27

Tillage and very heavy equipment (sugarcane production): soil structure is further degraded

Question 28

how does tillage and heavy equipment affect soil degredation and erosion?

Answer 28

Tillage and very heavy equipment (sugarcane production): soil structure is further degraded

Question 29

when native grasses are removed, what can happen to the soil? i.e. America 1930s

Answer 29

Ploughing and also livestock disturb the soil structure
Soils became highly susceptible to wind erosion

Question 30

how much does 1mm of soil from 1 hectare weigh?

Answer 30

4.5tons

Question 31

What are the 4 characteristics of chemical degradation

Answer 31

Depletion of organic matter and nutrients (from vegetation loss)
Contamination with chemical pollutants
Salinization – in dry areas (particularly with irrigation)
Desertification – only occurs in arid, semi-arid and dry sub-humid areas

Question 32

what causes salinzation?

Answer 32

Poor water management
Too much water evaporates from surface
Salts left behind
Toxic to plants

Question 33

what a consequence of soil acidification?

Answer 33

acid rain

Question 34

how does acid rain cause damage?

Answer 34

1. displaces nutrients from cation exchange sites –> leached away –> no longer available for plant growth
2. toxic aluminium is soluble in water at low pH (non-mobile and safe at neutral and high/ basic pH) injures plants and soil microorganisms

Question 35

other than acidifaction from acid rain, how else may this be caused?

Answer 35

excessive ammonium fertilisation via nitrification by soil microbes:
(NH4+ –>–> NO3- + H+)

Question 36

what does acid rain cause?

Answer 36

causes flooding of cation exchange sites on soil colloids with protons (H+)

Question 37

what is the Yield Plateaus

Answer 37

where production is maximised, but cannot grow. this is a threat to growing population.

Question 38

T/F Soil degradation is an additional threat to food security

Answer 38

True