Transcript Soil C Dynamics Following Addition of 13C-labeled Grain Sorghum (Sorghum bicolor) Residue Paul White and Dr.

Soil C Dynamics Following
Addition of 13C-labeled
Grain Sorghum (Sorghum
bicolor) Residue
Paul White and Dr. Charles W. Rice
Department of Agronomy
Kansas State University
Manhattan, KS
Carbon Sequestration
• Atmospheric CO2 levels have increased from 260 to
370 ppmv (IPPC, 2004).
• Increasing soil C storage may assist in offsetting
increases in CO2 due to fossil fuel emissions until
cleaner fuel technology is available on a large scale.
• Understanding dynamics of C flow in differently
managed ecosystems will be important to forecast Csequestration effectiveness and extent.
• Possible manipulation of ecosystem to increase soil
C storage potential
Sunlight
CO2
Temperature
Moisture
Inputs
Nutrients
Outputs
Substrate
Quality
Soil Belowground
Biology
INPUTS
Plant
residue
Readily
decomposable
CO2
Moderately
decomposable
CO2
Microbial
Biomass C
Resistant
CO2
CO2
Plant and microbial
byproducts
CO2 = OUTPUTS
CO2
Slow soil C
Stable soil C
Changes in microbial community
dynamics?
Temporal C
changes in soil
aggregates?
Adapted from Paul and Clark, 1996
Objectives
During one growing season:
• Measure the mineralization of 13C-labeled plant
residue
• Measure the changes in soil TC and TN
• Measure the changes in soil TC and 13C in macroand microaggregates
• Determine microbial community changes in
response to added residue
Materials and Methods
Ashland Experimental Farm,
Manhattan, KS
Field Microcosm Experiment
• Continuous Sorghum under NoTillage (NT) and Conventional
Tillage (CT)
• 4 Blocks
• 2 Residue Levels: Control (no
residue) and 0.5% by weight
• 7 Sample Times: 0, 3, 16, 25, 40,
68, and 159 d
• Data analyzed using SAS v9 Proc
Mixed and means separated at
the 5% significance level (SAS
Institute, Cary N.C).
Materials and Methods
Sorghum bicolor CV: Mycogen 1506
0.5X Hoagland’s
Pulse labeled 5X
with 100% 13CO2
Aboveground Residue Characteristics
Total C
13C
(PDB)
----%----
-----‰-----
42
570
Pre-boot stage
(about 65 d)
Above ground material
removed, freeze dried,
shredded, and the 4 to 6 mm
fraction retained for field
experiment
Materials and Methods
NT 2.1 g 13C labeled residue
placed on soil surface
20 cm deep by
5 cm diameter
PVC cores
15 cm
CT 2.1 g
Mixed evenly with
upper 15 cm soil with
soil
Anion and Cation
Exchange Resin bag
Materials and Methods
Sample Times:
0 3 16 25 40 68 159d
0 cm
5 cm
15 cm
Anion and Cation
Exchange Resin bag
Soil separated into 0-5 and 5-15
cm sections and sieved (4 mm)
and either air-dried, put in 4 °C
cooler, or freeze dried depending
on analysis.
Materials and Methods
C measurements
on a scaled
approach
Total % C and N
Overall system stability
13C
New input decomposition
and retention
Whole Soil
Aggregates (>1000 m,
250-1000 m, 53-250 m,
and 20-53 m)
Temporal C
changes in
aggregates?
Phospholipid Fatty Acids
Changes in microbial
community structure?
13C
Neutral Lipid Fatty Acids
Materials and Methods
Total % soil C, N by dry combustion & TCD
detection
13C
whole soil measured by conversion to CO2
using dry combustion and isotopic 13C
measured using Europa 20-20 IRMS.
13C
Data reported relative to the Pee Dee
Belemnite (1.12372% 13C, or 0‰)
Soil Chemical and Physical
Parameters and 2004
Climate Data
Soil: Muir silt loam
Tillage Depth pH P
Ca
K Mg Na SO4-S NH4-N NO3-N TC TN
1:1 -----------------------mg/kg------------------------
----%----
CT
0-5
5.4 128 1844 317 281 3.6 7.5
3.6
8.2 1.2 0.11
CT
5-15
5.7 52 2209 193 308 6.0 7.6
2.8
3.4 1.2 0.11
NT
0-5
5.0 158 1768 262 251 3.7 8.3
2.9
5.4 1.9 0.17
NT
5-15
5.8 41 2201 173 291 5.8 6.5
2.5
2.4 1.4 0.13
Bulk Density: NT=1.40 g/cm3 CT=1.36 g/cm3 (G. Doyle, Ph.D.
Dissertation)
Data reported on a Mg/ha to 15 cm depth basis
2004 Precipitation
200
180
Precip (mm)
160
140
120
100
80
60
40
20
0
Sample Times:
Jan Feb Mar Apr May Jun
Jul
Aug Sep Oct
Nov Dec
2004 Temperature
30
Mean Temp (C)
25
20
15
10
5
0
-5
Jan Feb Mar Apr May Jun
Jul
-10
Month
2004 Air Temperature
1980-2003 Air Temp
Aug Sep Oct
Nov Dec
Results
Total Soil C – Tillage X Depth Interaction
Time=2 Soil C
Time=1 Soil C
Time=0 Soil C
60
50
40
MgC/ha 30
20
10
0
a
a
b
a
0-5
5-15
0-5
5-15
CT
CT
NT
NT
60
50
40
MgC/ha 30
20
10
0
b
a
a
a
0-5
5-15
0-5
5-15
CT
CT
NT
NT
60
50
40
MgC/ha 30
20
10
0
0-5
5-15
0-5
5-15
CT
CT
NT
NT
Treatment
Treatment
Time=4 Soil C
Time=3 Soil C
Treatment
60
50
40
MgC/ha 30
20
10
0
60
50
40
MgC/ha 30
20
10
0
0-5
5-15
0-5
5-15
CT
CT
NT
NT
0-5
5-15
0-5
5-15
CT
CT
NT
NT
Treatment
Treatment
Time=5 Soil C
Time=6 Soil C
60
50
40
MgC/ha 30
20
10
0
0-5
5-15
0-5
5-15
CT
CT
NT
NT
Treatment
60
50
40
MgC/ha 30
20
10
0
0-5
5-15
0-5
5-15
CT
CT
NT
NT
Treatment
Total Soil N – Tillage X Depth Interaction
Time=1 Soil N
Time=2 Soil N
T=0 Soil N
5
4
MgN/ha
MgN/ha
3
5
5
4
4
3
MgN/ha
2
1
2
0
0
0-5
CT
5-15
CT
0-5
NT
2
1
0
1
3
5-15
0-5
5-15
0-5
5-15
0-5
5-15
0-5
5-15
CT
CT
NT
NT
CT
CT
NT
NT
Treatment
NT
Treatment
Time=4 Soil N
Time=3 Soil N
Treatment
MgN/ha
5
5
4
4
3
MgN/ha
3
2
2
1
1
0
0
0-5
5-15
0-5
5-15
0-5
5-15
0-5
5-15
CT
CT
NT
NT
CT
CT
NT
NT
Treatment
Treatment
Time=6 Soil N
Time=5 Soil N
MgN/ha
5
5
4
4
3
MgN/ha
3
2
2
1
1
0
0
0-5
5-15
0-5
5-15
0-5
5-15
0-5
5-15
CT
CT
NT
NT
CT
CT
NT
NT
Treatment
Treatment
CT 0-5 13C remaining
during experiment
Kinetics modeled as
first order having a
rapid and slow phase
according to:
6
Ct=Co-ekt
5.5
ln100+13C
CT0-5block1
CT0-5block2
CT0-5block3
CT0-5block4
5
4.5
0
10
20
30
40
Time (d)
50
60
70
80
CT 5-15 13C remaining
during experiment
6
5.5
100+ln13C
CT5-15block1
CT5-15block2
CT5-15block3
CT5-15block4
5
4.5
0
10
20
30
40
time (d)
50
60
70
80
NT 0-5 13C remaining
during experiment
6
5.5
NT0-5block1
NT0-5block2
NT0-5block3
NT0-5block4
5
4.5
0
10
20
30
40
50
60
70
80
Residue Decomposition Kinetics
Rapid
Slow
---------k/day------------0.0316
-0.0024
By T=5, no significant difference
between tillage or depth in remaining
total amount of 13C in soil:
0-15 cm average 13C
--------‰ (PDB)--------
CT
+28.66
NT
+34.63
Conclusions
• Addition of 0.5% by weight grain sorghum
residue did not have significant impacts on soil C
and N dynamics during the growing season
Indicating relative macro system stability
• Decomposition kinetics and residual 13C levels
were not different between tillage regimes
Label detectable throughout growing season
•
13C
Aggregate analysis and microbial lipids
analysis may indicate management effects at a
finer resolution
Acknowledgments
• Geronimo Watson, Karina Fabrizzi, Jamey
Duesterhaus, and undergraduate lab techs
• Dr. Chuck Rice
• Dr. Mary-Beth Kirkham
• Dr. Clenton Owensby
• Dr. Dallas Pederson
This material is based upon work supported by the Cooperative State
Research, Education, and Extension Service, U.S. Department of
Agriculture, Under Agreement No. 2001-38700-11092.