som long term trials
TRANSCRIPT
Soil organic matter and long-term agricultural experiments
Johan Six
University of California - Davis
Questions
• Quantity versus quality?
• Is stable SOM predominantly microbial in origin?
• SOM dynamics at steady state?
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0.4
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0.8
1.0
1.2
1.4
Maize Calliandra Tithonia
So
il o
rga
nic
C (
g C
kg
-1 s
oil)
Silt + Clay
Microaggregates
Macroaggregates
Residue-Derived Soil C - 0.25 yr
B
AA
Gentile et al 2008 SBB
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Maize Calliandra Tithonia
So
il o
rga
nic
C (
g C
kg
-1 s
oil)
Silt + Clay
Microaggregates
Macroaggregates
Residue-Derived Soil C - 1.5 yr
AAA
Gentile et al 2008 SBB
0
5
10
15
20
25
30
35
40
45
Control Maize Calliandra Tithonia
Soil
org
an
ic C
(g C
kg
-1 s
oil)
Silt + Clay
Microaggregates
Macroaggregates
Soil Organic Matter Stabilization
B
A A A
Gentile et al 2011 Ecol Appl
0
10
20
30
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50
60
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100
C In
pu
t (M
g C
ha-1
)
RWC IWC RWF IWF RWL IWL CWT LCT CCT OCT
Russell Farm Cropping Systems
Kong et al. 2005 SSSAJ
C input
Carbon Saturation Model
m
t
C
Ik
IC
mC
C-Input (I)
So
il C
-co
nte
nt
(Ct)
k
SOC at equilibrium time
Inputs = Outputs
mC
k
= maximum SOC content
= rate of C saturationCSAT Model
Six et al 2002 Plant Soil
Carbon Saturation Model
m
t
C
Ik
IC
mC
C-Input (I)
So
il C
-co
nte
nt
(Ct)
k
SOC at equilibrium time
Inputs = Outputs
mC
k
= maximum SOC content
= rate of C saturation
C-Input (I)
Linear Model
k
ICt
CSAT Model
Six et al 2002 Plant Soil
Saturation vs steady state
Soil C equilibrium
Carbon
content
Equilibrium level
input > respiration
{input = respiration
Time
increased
inputs result in
new equilibrium
Carbon
content
Equilibrium level
input > respiration
{input = respiration
Time
increased
inputs result in
new equilibrium
C content versus time, C inputs are constantSoil C equilibrium
Carbon
content
Equilibrium level
input > respiration
{input = respiration
Time
increased
inputs result in
new equilibrium
Carbon
content
Equilibrium level
input > respiration
{input = respiration
Time
increased
inputs result in
new equilibrium
C content versus time, C inputs are constantSoil C equilibrium
Carbon
content
Equilibrium level
input > respiration
{input = respiration
Time
increased
inputs result in
new equilibrium
Carbon
content
Equilibrium level
input > respiration
{input = respiration
Time
increased
inputs result in
new equilibrium
C content versus time, C inputs are constant
West & Six 2007
Carbon Saturation Lethbridge, Alberta
Gulde et al. 2008 SSSAJ
Dark Brown Chernozemic (Typic Haplustoll) Clay Loam Annual manure additions since 1973
mC
Distinct Saturation behavior of SOC poolsSite
soil USDA sand silt clay MAT MAP
texture classification (% composition) (° C) (mm)
Lethbridge, Alberta LT clay loam Typic Haplustoll 31 39 30 5.9 389
Lexington, KY KY silt loam Typic Paleudalf 5 68 27 12.7 547
Malhi, Alberta MH silty clay loam Typic Cryoboroll 0-19 45-64 36 1.7 452
Breton, Alberta AB loam Typic Cryoboralf 31 39 30 3.9 240
Scott, Saskatchewan. SC clay loam Typic Boroll 28 44 28 2.4 483
1
Carbon SaturationCutin + Suberin (SFA) Response
VSC = lignin SFA = cutin + suberin
Carrington et al 2012 SBB
Answers
• Is stable SOM predominantly microbial in origin?
it looks like
• SOM dynamics at steady state?
we need to consider C saturation
• Quantity versus quality?
Quantity!
Answers like this can only be answered through long-term experiments linked to biogeochemical models
… the saturation level of a soil, in combination with the initial soil C or steady state level,
determines the rate and duration of potential C sequestration. (West and Six, 2007)
Innate property of a soil Independent of climate, redox, and land management. Impacts how land use change can increase soil organic carbon stocks.
Soil Carbon Saturation
(Hassink, 1996)
Carbon SaturationConclusions
• Preferential Stabilization or Preservation:– Lignin, cutin, and suberin are not preserved by inherent
recalcitrance.
– Lignin, cutin, and suberin stabilization does not change
with C saturation, despite decreasing C stabilization
potential.
Carrington et al 2012 SBB
Carbon SaturationConclusions
• Preferential Stabilization or Preservation:– Lignin, cutin, and suberin are not preserved by inherent
recalcitrance.
– Lignin, cutin, and suberin stabilization does not change
with C saturation, despite decreasing C stabilization
potential.
• Microbial v. Plant-Derived C – There is no preferential stabilization of microbial C in the
chemically protected fraction with C saturation.
– Microbial C may preferentially accumulate in the non-
protected and aggregate fractions with C saturation.
Carrington et al 2012 SBB
Carbon SaturationConclusions
• Preferential Stabilization or Preservation:– Lignin, cutin, and suberin are not preserved by inherent
recalcitrance.
– Lignin, cutin, and suberin stabilization does not change
with C saturation, despite decreasing C stabilization
potential.
• Microbial v. Plant-Derived C – There is no preferential stabilization of microbial C in the
chemically protected fraction with C saturation.
– Microbial C may preferentially accumulate in the non-
protected and aggregate fractions with C saturation.
• Quantity, not Quality– Only quantity affects the chemical saturation response.
Carrington et al 2012 SBB