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Lecture 24

AGR 2050 Lecture Notes - Lecture 24: Soil Health, Soil Respiration, Carbon Cycle

11 pages79 views2018

Department
Agriculture
Course Code
AGR 2050
Professor
Clarence J Swanton
Lecture
24

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Wednesday, March 21, 2018
Carbon Cycling & SOM
Carbon Cycle
Describes the movement of carbon as it is recycled & reused throughout the
biosphere
Involves the incorporation of carbon dioxide into living tissue by
photosynthesis & its return to the atmosphere through respiration, the decay
of dead organisms, & the burning of fossil fuels
The story of life
o Plant residue composition
Commented [A1]: Photosynthesis & the lifecycle
depend on this
Commented [A2]: When the carbon in the
atmosphere increases, what does this do to the
earth?
Commented [A3]: Influence the carbon cycle:
OM
Soil health
pH
Temperature
Weather
Commented [A4]: Climate change: how will it
change? How will it affect our change to this?
Commented [A5]: Humans are a part of the cycle
Commented [A9]: Photosynthesis: transfer of solar
energy into useful plant energy
Uses carbon dioxide (from the atmosphere) - to
ATP to cellulose
We eat the plants (absorption of energy)
Expire & respire to put carbon dioxide back
into the atmosphere
Commented [A8]: Top: farm carbon cycle
(harvesting crops, etc.)
Commented [A7]: Residue on surface: how long it
takes to breakdown
Proteins: do not decompose easily more
complex
Carbohydrates
Different forms of carbon
Commented [A6]: If the cycle is slow or delayed
(something wrong below the ground) there are
ways that we can help this process
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Climate Change & Carbon
Carbon cycle is an important part of the processes influencing atmospheric
carbon
Current atmospheric level = 370 ppm
CO2 levels in year 2100 estimated to be 500-1000ppm
Year 2100 expect;
o Temperature change between 1.5 & 5.5 degrees
o Soil warming will decrease carbon storage
o Sea level change 0.1-0.9 m
Largest Carbon Pool
Its not so much about averages
o As the extremes
Commented [A10]: No one truly knows where it is
going to be, at least a doubling
Commented [A11]: Talking about at the equator à
(2°C at the equator to 6°C at the pole)
Commented [A12]: Will make New York city sink
Commented [A13]: Biosphere connects: Atmosphere
(air), Hydropshere (water),
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§ We have to adapt our production systems to maintain high
yields under those conditions
Research is needed to understand the interaction of climate change &
carbon cycle
o At this time, the understanding of this interaction is incomplete
Soil Respiration & Global Carbon Cycle
Soil respiration
o Is the primary path by which CO2 fixed by plants returns to the
atmosphere
o Increases with temperature
Rising concentrations of CO2 in the atmosphere will increase the flux of CO2
from soils
Soil carbon pool unlikely to moderate the rise in atmospheric CO2
Flux of CO2 from soils tied to plant growth with supplies OM to decomposers
o Lower organic matter in the tropics (rainforests decomposes faster)
than here
Greatest rate of soil respiration is found in the tropics where plant growth is
luxuriant & conditions ideal for decomposers
Greatest loss in soil carbon in tropics as temperature increases
OM increase not from large biomass inputs but rather from other factors
(temperature) that limits decomposers
o That is why we have higher organic matter (more C within the soil)
Tillage increases rate of OM decomposition because of soil aeration, moisture
content & higher rates of soil respiration
o Holland marsh is 70% organic matter, but every time they till, they loss a
little bit of their soil
Tillage disrupts soil aggregates, exposing absorbed OM to decomposition
Loss of OM lower in no-till
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