Soil 8 - Coil C and OM Flashcards
What is soil health?
the continued capacity of a soil to function
- intersection of biological, physical, chemical qualities
What are some soil ecosystem services?
Nutrient cycling, water/air, support/plant medium, habitat/biodiversity:
- carbon storage
- GHG uptake
- food/fuel/fibre
- pollination, wildlife habitat
- water purification
What environmental crises does agriculture concern?
- biodiversity crisis
- soil carbon crisis
- climate crisis
where does the long-term carbon cycle happen?
- tectonics (volcanoes, seafloor spread, weathering)
Where does the short-term carbon cycle take place?
terrestrial! soil, plants, animals, atmosphere
What is SOM?
soil organic matter
- plant/animal/organic matter in various stages of decomposition
What breaks down in decomposition?
bonds in molecules
- proteins, sugars/starches, structural polysaccharides
What is the equation for decomposition?
Lt = L0 * e^-kt
(L = leaching)
What are the 4 phases of decomposition?
- Leaching of soluble cells
- fragmentation/chemical alteration/leaching of decay products
- chemical alteration
- mixing/adherance to mineral surfaces (MAON)
What environmental factors influence decomposition?
- temperature, moisture, access to substrate
- substrate quality/quantity
- biological drivers
What are other terms for ‘rapid’ and ‘slow’ decomposing molecules?
rapid = labile
slow = recalcitrant
What happens as OM decreases in particle size in decomposition?
decomposition slows down!
- more opportunities to protect against future decomposition
Why is humus maybe not a thing?
no experimental evidence supports the formation of large, persistent ‘humic substances’ in soil
What is the main shift in our modern understanding of SOC?
Traditionally thought that SOC comes from leaf litter, but soil microbes are a bigger carbon pool and flow than we thought
What is the rhizosphere?
all the soil directly on the roots, which provide nutrients for soil microbes
- contrast with low C bulk soil, in a natural state of starvation
What are root exudates?
low-weight compounds released into the root environment
- differ depending on plant species, crop development, abiotic factors
What is the importance of biota in the C cycle?
- Carbon pump microbes
- macrofauna bring nutrients downward, leave more extracellular substances (ex worm slime)
- also chewing + shredding - macrofauna mix the soil!
What are 3 ways soil C is destabilized?
- more CO2 in air
- C desorption (becomes dissolved C)
- increased microbial C metabolism
What are 4 ways climate change impacts the C cycle?
- more CO2 affects photosynthesis
- change in freeze-thaw cycles
- drought timing/intensity
- temperature
How permanent is soil C?
depends on the upper limit of mineral capacity to hold C (C can cycle between mineral, dissolved, organic sites), and plant/microbe biomass
What are the 2 main global changes affecting soils?
- agriculture
- climate change
What are the 2 new ‘knowns’ in C cycling?
- low molecular weight, labile molecules (usually from microbes) persist longer than chemically recalcitrant C structures when protected by organo-mineral complexation (ie when C attaches to soil minerals)
- Each soil type has a finite limit to how much C it can store on mineral surfaces
What is the MEMS model of soil C cycling?
Microbial Efficiency Matrix Stabilization
- set of pools and flows in atmosphere, soil, deep soil
What part of regenerative agriculture techniques is accurate?
changing grazing and rotations does affect SOC
What are 2 goals for increasing SOC in regenerative agriculture?
- improve soil health and biodiversity
- non-inorganic amendments and living roots
Are SOC increases predictable and linear?
no to both!
What are the 2 main influences in C storage capacity?
- OM inputs
- soil texture
Where are the greatest opportunities to increase SOC?
low-yielding regions
What are 4 soil management regenerative practices?
- keep soil in place/covered
- minimize disturbances and extremes
- maximize living roots
- return residues to soil
What do good soil management practices do for the microbiome?
increase abundance (capacity) and diversity (resilience) of community
What is a big future debate in SOC management?
hoard it or use it? (build an ecosystem or a farm?)
How is Miscanthus grass relevant to N cycles?
lots of Nosz genes, so takes up a lot of N
What model does decomposition follow?
Continuum model!
