Soil%20C%20Dynamics%20Following%20Addition%20of%2013C-labeled%20Grain%20Sorghum%20(Sorghum%20bicolor)%20Residue

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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

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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
  C-sequestration effectiveness and extent.
• Possible manipulation of ecosystem to increase
  soil C storage potential

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Sunlight Temperature Moisture Nutrients
CO2
Inputs
Outputs
Substrate Quality
Soil Belowground Biology
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INPUTS
Plant residue
CO2
CO2
CO2
Microbial Biomass C
Plant and microbial byproducts
CO2
CO2
OUTPUTS
CO2
Slow soil C
Stable soil C
Temporal C changes in soil aggregates?
Changes in microbial community dynamics?
Adapted from Paul and Clark, 1996
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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 macro-
  and microaggregates
• Determine microbial community changes in response
  to added residue

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Materials and Methods
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Ashland Experimental Farm, Manhattan, KS
Field Microcosm Experiment

• Continuous Sorghum under No-Tillage (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).

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Materials and Methods
Sorghum bicolor CV Mycogen 1506
0.5X Hoaglands
Pulse labeled 5X with 100 13CO2
Pre-boot stage (about 65 d)
Above ground material removed, freeze dried,
shredded, and the 4 to 6 mm fraction retained for
field experiment
Aboveground Residue Characteristics Total C
13C (PDB) -------- ----------
42 570
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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
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Materials and Methods
Sample Times
0 3 16 25 40 68 159d
0 cm
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.
5 cm
15 cm
Anion and Cation Exchange Resin bag
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Materials and Methods
C measurements on a scaled approach
Total C and N 13C Whole Soil 13C Aggregates
(gt1000 ?m, 250-1000 ?m, 53-250 ?m, and 20-53
?m) Phospholipid Fatty Acids Neutral Lipid Fatty
Acids
Overall system stability
New input decomposition and retention
Temporal C changes in aggregates?
Changes in microbial community structure?
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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)
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Soil Chemical and Physical Parameters and 2004
Climate Data
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Soil Muir silt loam
Tillage Depth pH P Ca K Mg Na
SO4-S NH4-N NO3-N TC TN
11 -----------------------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 NT1.40 g/cm3 CT1.36 g/cm3 (G.
Doyle, Ph.D. Dissertation) Data reported on a
Mg/ha to 15 cm depth basis
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2004 Precipitation
Sample Times
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2004 Temperature
2004 Air Temperature 1980-2003 Air Temp
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Results
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Total Soil C Tillage X Depth Interaction
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Total Soil N Tillage X Depth Interaction
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CT 0-5 13C remaining during experiment
Kinetics modeled as first order having a rapid
and slow phase according to CtCo-ekt
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5.5
CT0-5block1
ln10013C
CT0-5block2
CT0-5block3
CT0-5block4
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4.5
0
10
20
30
40
50
60
70
80
Time (d)
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CT 5-15 13C remaining during experiment
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NT 0-5 13C remaining during experiment
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Residue Decomposition Kinetics
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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

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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.
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