Soils Lecture 3- Marc Flashcards
in soil types, which stores the most Carbon?
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
What services are provided by our soil?
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
name some of the organisms which live in soil
nematodes
microbes
fungal hyphae
fungi
mites
springtails
what is humus?
Humus is carbon that has resisted degradation
characteristics of humus?
VERY slowly decomposed
Plant and microbial origin
Provides soil with its dark colour, especially in the A horizon
what is the A horizon, when considering humus and soil
A horizon is the most biologically active layer, with higher organic matter and nutrients
What is the exchange mechanism responsible for nutrient retention
Cation exchange
what are Colloids?
Colloids are the smallest particles: of clay (mineral) or humus (organic) chemically active
Mainly negatively charged
what would make a good soil?
one with High CEC = high nutrient
retention and good soil
fertility
Caiton Exchange Capacity
which element is a Cation which can affect soil pH?
H+
list things that will affect soil fertility
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
how is soil fertility defined?
the ability to sustain plants
define the following:
GEP:
ER:
NEP:
Gross ecosystem productivity (photosynthesis)
R: Ecosystem respiration
NEP: Net ecosystem productivity
define GEP
Gross ecosystem productivity (photosynthesis)
Define ER
ER: Ecosystem respiration
define NEP
NEP: Net ecosystem productivity
how are some of the ways forest soils fix carbon?
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)
how do forest soils lock in Methane and N2O
CH4 uptake by methane-oxidizing soil bacteria
N2O efflux through microbial nitrification and denitrification processes
how do forest soils lock in Methane and N2O
CH4 uptake by methane-oxidizing soil bacteria
N2O efflux through microbial nitrification and denitrification processes
how much carbon do peatlands hold globally
1/3
how much carbon do peatlands hold globally
1/3
what can a High water-table cause?
(when precipitation is ample) leads to anoxia, slow decomposition, but greater CH4 emissions
why does Sphagnum peat decomposes slowly in bogs?
It is flooded, which makes it anoxic/anaerobic
It is acidic
It is nutrient poor
what is peat subsidence?
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
what is peat subsidence?
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
how does pasture grazers affect soil degredation and erosion?
compaction due to hoof traffic often associated with over-grazing
how does tillage and heavy equipment affect soil degredation and erosion?
Tillage and very heavy equipment (sugarcane production): soil structure is further degraded
how does tillage and heavy equipment affect soil degredation and erosion?
Tillage and very heavy equipment (sugarcane production): soil structure is further degraded
when native grasses are removed, what can happen to the soil? i.e. America 1930s
Ploughing and also livestock disturb the soil structure
Soils became highly susceptible to wind erosion
how much does 1mm of soil from 1 hectare weigh?
4.5tons
What are the 4 characteristics of chemical degradation
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
what causes salinzation?
Poor water management
Too much water evaporates from surface
Salts left behind
Toxic to plants
what a consequence of soil acidification?
acid rain
how does acid rain cause damage?
- displaces nutrients from cation exchange sites –> leached away –> no longer available for plant growth
- toxic aluminium is soluble in water at low pH (non-mobile and safe at neutral and high/ basic pH) injures plants and soil microorganisms
other than acidifaction from acid rain, how else may this be caused?
excessive ammonium fertilisation via nitrification by soil microbes:
(NH4+ –>–> NO3- + H+)
what does acid rain cause?
causes flooding of cation exchange sites on soil colloids with protons (H+)
what is the Yield Plateaus
where production is maximised, but cannot grow. this is a threat to growing population.
T/F Soil degradation is an additional threat to food security
True
