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![Page 1: Introduction to the science of agricultural emissions and sinks This presentation provides participants with a basic understanding of the soil, plant and.](https://reader030.fdocuments.us/reader030/viewer/2022033023/56649cb75503460f9497dc8c/html5/thumbnails/1.jpg)
Introduction to the science of agricultural emissions and sinks
This presentation provides participants with a basic understanding of the soil, plant and animal carbon and nitrogen cycles and explains the science behind agriculture emissions and how these affect the atmosphere and the role of sinks in the global carbon budget
Source:University of Melbourne, UoM June 2013
![Page 2: Introduction to the science of agricultural emissions and sinks This presentation provides participants with a basic understanding of the soil, plant and.](https://reader030.fdocuments.us/reader030/viewer/2022033023/56649cb75503460f9497dc8c/html5/thumbnails/2.jpg)
The Carbon cycle
http://www.davidsuzuki.org/files/CCcarboncycle.GIF
C-stocks in Pg (Gt), C-fluxes in Pg yr-1; Pg = 1015g = 1 Gt (gigatonne)
• More carbon emissions than carbon uptake fossil fuel emissions
• Increase carbon sinks – increase terrestrial plant or soil sinks
• Large carbon pools, relatively small fluxes between pools
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Global forest distribution
www.fao.org/forestry
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Sources of global CO2 emissions
12% of total anthropogenic
emissionsLe Quéré et al. 2009, Nature-Geoscience; Data: CDIAC, FAO, Woods Hole Research Center 2009
Slide courtesy of J. Canadell, Global Carbon Project
Fossil fuel
Land use change
10
8
6
4
2
1960 20101970 1990 20001980
CO2 e
miss
ions
(PgC
y-1)
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Carbon stocks and sequestration
Carbon stock/pools
Carbon sequestration
How much C at one point in time
Change of C stock over time
Aboveground biomassLeaves, stem, branches
Below ground biomassCoarse roots, fine roots, microbes
Soil carbonStable and labile fractions
Litter & coarse woody debris
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NPP
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Net primary productivity
Tropical forest are the most productive
Forests produce most of the terrestrial carbon
Saugier (2001) IN: Terrestrial Global Productivity
NP
P (
t C
ha-1
yr-1
)
-2
0
2
4
6
8
10
12
14
NPP blowground
NPP aboveground
0.5 2.6 8.1 21.9 14.9 7.0 3.5 4.1 NPP Pg C yr -1
Crops produce mainly aboveground NPP consequences for soil C
belowgroundaboveground
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The Carbon cycle
• Human activity greatly influences the global C cycle
• The sink capacity of natural CO2 sinks is decreasing, leading to increased atmospheric CO2
• Forest ecosystems are the greatest carbon sink in the
terrestrial biosphere
• Globally, soils store more C than biomass
• The capacity of an ecosystem to store C is determined by the balance of C uptake (photosynthesis) and C loss (respiration)
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Grazing system carbon cycle
• The carbon cycle in animal production systems and the various pools of carbon
• Fluxes between carbon pools • Methane, carbohydrate, carbon dioxide
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Grazing system carbon cycle
• Terms used:– Hydrogen (H2), Carbon (C), Oxygen (O2),
Nitrogen (N)– Methane (CH4), carbohydrate (CHO),
carbon dioxide (CO2), water (H2O), bicarbonate (HCO3)
– Nitrate (NO3-), Nitrite (NO2
-), Ammonia (NH3), Ammonium (NH4
+), nitrous oxide (N2O)
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Grazing system carbon cycle
• Atmosphere• Animal• Plant• Soil
Photosynthesis
CO2 in atmosphere
Consumption
Respiration
Mineralisation Crop and animal Residues
Carbon in soilOrganic matter
Decomposition inmicrobes
Humus and aggregate
formulation
Eckard 2011
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Grazing system carbon cycle
• Carbon into plants– Photosynthesis
• CO2 + H2O + chlorophyll + solar energy -> CHO + O2
• Structural carbohydrate– Cellulose, hemi-cellulose, lignin
• Non-structural carbohydrate– Sugars
• Fats/ Lipids• Protein/amino acids
• Carbon from plants– Respiration
• Burning sugars - energy for growth• O2 + CHO -> H2O + CO2 + energy
– Decay of plant residues• Mineralisation to CO2
Photosynthesis
CO2 in atmosphere
Consumption
Respiration
Mineralisation Crop and animal Residues
Carbon in soilOrganic matter
Decomposition inmicrobes
Humus and aggregate
formulation
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Grazing system carbon cycle
Photosynthesis Respiration
Produces sugars from energy Burns sugars for energy
Energy is stored Energy is released
Occurs only in cells with chloroplasts Occurs in most cells
Oxygen is produced Oxygen is used
Water is used Water is produced
Carbon dioxide is used Carbon dioxide produced
Requires light Occurs in dark and light
Comparison of Photosynthesis & Respiration
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Grazing system carbon cycle
• Carbon into the animal• Structural carbohydrate
– Cellulose, hemi-cellulose, lignin
• Non-structural carbohydrate– Sugars
• Fats/ Lipids• Protein/amino acids
• Carbon from the animal• As above in products (meat, milk, fibre)• CH4 and CO2 – microbial digestion and
respiration
Photosynthesis
CO2 in atmosphere
Consumption
Respiration
Mineralisation Crop and animal Residues
Carbon in soilOrganic matter
Decomposition inmicrobes
Humus and aggregate
formulation
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Grazing system carbon cycle
The Rumen Simple stomach
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Grazing system carbon cycle
• Fluxes between carbon pools– Into soil
• Plant and animal residues• Microbes
– From soil• Microbial decomposition• Organic Carbon to CO2 and CH4
Baldock 2009
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Grazing system carbon cycle
Humus (~stable)<0.053 mm
RespirationPhotosynthesis
CHO
Plant ResiduesLitter > 2mm
POC (~labile)> 0.053 mm
Carbon dioxide (CO2)
DecompositionMicrobial Biomass
MineralisationMethane (CH4)Nitrous Oxide
(N2O)
Baldock et al. 2009; Eckard, 2009
Nutrients
In established pastures Photosynthesis ≈ Respiration + Mineralisation Photosynthesis ≠ Respiration + Mineralisation + Methane
Decay
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The nitrogen cycle in agricultural systems
• The nitrogen cycle in agricultural systems• Fluxes between nitrogen pools• Forms of nitrogen and their fate
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The nitrogen cycle
Whitehead 1995
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The nitrogen cycle
• Atmosphere– N2 (nitrogen)
• 78% of the atmosphere– O2 = 21%, CO2 = 0.04%
• Fixed by legumes into plants and soil
– N2O (nitrous oxide)• 0.32 ppm (0.00003%)
Eckard 2011
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The nitrogen cycle
• Main forms of soil & plant N– NH3 – Ammonia
• Organic matter• Fertilisers
– Urea, DAP, UAN etc.
• Major source of plant N
Eckard 2011
oxygen
amide ionamide ion
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The nitrogen cycle
• Main forms of soil & plant N– NH4
+ – Ammonium• Soil solution• Loosely bound on cation exchange
– Positive charge attached to clay» Exchangeable » Clay-fixed (non-exchangeable)» Does not readily leach
• Major source of plant N (nitrogen)– Preferential uptake in colder, wetter soils
• Rapidly converts to NO3- (nitrate ion)
– In warm, well-drained soils
Eckard 2011
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The nitrogen cycle
• Main forms of soil & plant N– NO3 (nitrate ion)
• Major source of plant nutrition– Drier soils
• Accumulates in some plants– e.g. Brassicas, annual ryegrass, kikuyu, cereal grains– Breaks down to NO2 in rumen – toxicity
• Soluble in water – leaches
– NO2 (nitrite ion)• Transient in plants and soils• Main form of toxicity in ruminants
Eckard 2011
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The nitrogen cycle
• Main forms of soil & plant N– Soil organic matter N
• Decomposed residues– Amides, proteins etc
• Microorganisms (microbial biomass)• C: N ratio
– Usually 10:1 to 40:1
• Major source of plant N– Through mineralisation
Eckard 2011
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The nitrogen cycle
• Mineralisation– Microbial breakdown of soil organic matter to ammonium– The main mechanism for supplying N to plants
• Nitrification– Microbial conversion of ammonium to nitrate
• Ammonia sources– Urine, decaying organic matter, fertiliser
• Warm, moist (not waterlogged) soils• Denitrification
– Microbial conversion of nitrate to N2 and N2O gasses• Warm, waterlogged soils• N2O is a powerful greenhouse gas
• Immobilisation– Microbial assimilation of soil nitrogen into OM
OM
NH4+
NO3-
N2 N2O
Eckard 2011
organic matter
ammonium ion
nitrous oxidenitrogen
nitrate ion
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The nitrogen cycle
• Nitrogen balances in Agricultural systems – Biological efficiency
• Less than 50%
N Inputs Dairy Grains
N fertiliser 150 90N2 fixation 80 0Atmosphere 8 8Feed 45 0Total Input 283 98N output in productMilk 80Meat 8Grain 40Total Outputs 88 40N Surplus 195 58Efficiency (%) 31 41
Eckard et al 2007
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© Copyright 2013 The University of Melbourne, The Carbon Market Institute and the Department of Agriculture, Fisheries and Forestry, Carbon Farming Futures, Extension and Outreach Program