Soil C Dynamics Following Addition of 13C-labeled

Grain Sorghum (Sorghum bicolor) Residue

Paul White and Dr. Charles W. RiceDepartment of Agronomy

Kansas State University

Manhattan, KS

Carbon SequestrationCarbon 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

Soil Belowground Soil Belowground BiologyBiology

COCO22

SunlightSunlight

TemperatureTemperature

MoistureMoisture

NutrientsNutrients

Substrate Substrate QualityQuality

InputsInputs

OutputsOutputs

Adapted from Paul and Clark, 1996

Readilydecomposable

Moderatelydecomposable

ResistantPlant residue

CO2

CO2 CO2

Slow soil CStable soil C

CO2

CO2

Microbial Biomass C

Plant and microbialbyproducts

CO2

INPUTSINPUTS

= OUTPUTS= OUTPUTS

Temporal C Temporal C changes in soil changes in soil aggregates?aggregates?

Changes in microbial community Changes in microbial community dynamics?dynamics?

ObjectivesObjectives

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

Materials and MethodsMaterials and Methods

Ashland Experimental Farm, Manhattan, KS

• Continuous Sorghum under No-Continuous Sorghum under No-Tillage (NT) and Conventional Tillage (NT) and Conventional Tillage (CT)Tillage (CT)

• 4 Blocks4 Blocks

• 2 Residue Levels: Control (no 2 Residue Levels: Control (no residue) and 0.5% by weightresidue) and 0.5% by weight

• 7 Sample Times: 0, 3, 16, 25, 40, 7 Sample Times: 0, 3, 16, 25, 40, 68, and 159 d68, and 159 d

• Data analyzed using SAS v9 Proc Data analyzed using SAS v9 Proc Mixed and means separated at the Mixed and means separated at the 5% significance level (SAS Institute, 5% significance level (SAS Institute, Cary N.C).Cary N.C).

Field Microcosm ExperimentField Microcosm Experiment

Materials and MethodsMaterials and Methods

0.5X Hoagland’s 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

Sorghum bicolorSorghum bicolor CV: Mycogen 1506 CV: Mycogen 1506

Anion and Cation Exchange Resin bag

NT 2.1 g 13C labeled residue placed on soil surface

CT 2.1 g

Mixed evenly with upper 15 cm soil with soil

15 cm15 cm

20 cm deep by 20 cm deep by 5 cm diameter 5 cm diameter PVC coresPVC cores

Materials and MethodsMaterials and Methods

Materials and MethodsMaterials and Methods

0 cm

5 cm

15 cm

Anion and Cation Exchange Resin bag

Soil separated into 0-5 and 5-15 Soil separated into 0-5 and 5-15 cm sections and sieved (4 mm) cm sections and sieved (4 mm) and either air-dried, put in 4 and either air-dried, put in 4 °°C C cooler, or freeze dried depending cooler, or freeze dried depending on analysis.on analysis.

Sample Times:

0 3 16 25 40 68 159d0 3 16 25 40 68 159d

Total % C and N

13C Whole Soil

13C Aggregates (>1000 m, 250-1000 m, 53-250 m, and 20-53 m)

Phospholipid Fatty Acids

Neutral Lipid Fatty Acids

Temporal C Temporal C changes in changes in aggregates?aggregates?

Changes in microbial Changes in microbial community structure?community structure?

Overall system stabilityOverall system stability

New input decomposition New input decomposition and retentionand retention

C measurements C measurements on a scaled on a scaled approachapproach

Materials and MethodsMaterials and Methods

Total % soil C, N by dry combustion & TCD Total % soil C, N by dry combustion & TCD detectiondetection

1313C whole soil measured by conversion to COC whole soil measured by conversion to CO22

using dry combustion and isotopic using dry combustion and isotopic 1313C C measured using Europa 20-20 IRMS.measured using Europa 20-20 IRMS.

1313C Data reported relative to the Pee Dee C Data reported relative to the Pee Dee Belemnite (1.12372% Belemnite (1.12372% 1313C, or 0C, or 0‰‰))

Materials and MethodsMaterials and Methods

Soil Chemical and Physical Soil Chemical and Physical Parameters and 2004 Parameters and 2004

Climate DataClimate Data

Soil: Muir silt loamSoil: Muir silt loam

TillageTillage Depth Depth pHpH P P CaCa K K MgMg Na Na SOSO44-S-S NH NH44-N -N NONO33-N-N TC TC TNTN

1:11:1 -----------------------mg/kg------------------------ ---- -----------------------mg/kg------------------------ ----%----%----

CTCT 0-50-5 5.45.4 128 128 18441844 317 317 281281 3.6 3.6 7.57.5 3.6 3.6 8.28.2 1.2 1.2 0.110.11

CTCT 5-155-15 5.75.7 52 52 22092209 193 193 308308 6.0 6.0 7.67.6 2.8 2.8 3.43.4 1.2 1.2 0.110.11

NTNT 0-50-5 5.05.0 158 158 17681768 262 262 251251 3.7 3.7 8.38.3 2.9 2.9 5.45.4 1.9 1.9 0.170.17

NTNT 5-155-15 5.85.8 41 41 22012201 173 173 291291 5.8 5.8 6.56.5 2.5 2.5 2.42.4 1.4 1.4 0.130.13

Bulk Density: NT=1.40 g/cmBulk Density: NT=1.40 g/cm33 CT=1.36 g/cm CT=1.36 g/cm3 3 (G. Doyle, Ph.D. (G. Doyle, Ph.D. Dissertation)Dissertation)

Data reported on a Mg/ha to 15 cm depth basisData reported on a Mg/ha to 15 cm depth basis

2004 Precipitation2004 Precipitation

0

20

40

60

80

100

120

140

160

180

200

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Pre

cip

(mm

)

Sample Times:

2004 Temperature2004 Temperature

-10

-5

0

5

10

15

20

25

30

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Mea

n T

emp

(C

)

2004 Air Temperature2004 Air Temperature

1980-2003 Air Temp1980-2003 Air Temp

ResultsResults

Total Soil C Total Soil C –– Tillage X Depth InteractionTillage X Depth Interaction

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=0 Soil C

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=1 Soil C

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=2 Soil C

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=3 Soil C

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=4 Soil C

Treatment

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Time=5 Soil C

010

20304050

60

MgC/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=6 Soil C

aa aa aabb

aa aa aabb

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=1 Soil N

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

T=0 Soil N

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=2 Soil N

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=3 Soil N

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=4 Soil N

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=5 Soil N

0

1

2

3

4

5

MgN/ha

0-5 5-15 0-5 5-15

CT CT NT NT

Treatment

Time=6 Soil N

Total Soil N Total Soil N –– Tillage X Depth InteractionTillage X Depth Interaction

CT 0-5 CT 0-5 1313C remaining C remaining during experimentduring experiment

4.5

5

5.5

6

0 10 20 30 40 50 60 70 80

Time (d)

ln10

0+

13

C CT0-5block1

CT0-5block2

CT0-5block3

CT0-5block4

Kinetics modeled as Kinetics modeled as first order having a first order having a rapid and slow phase rapid and slow phase according to: according to:

CCtt=C=Coo-e-ektkt

CT 5-15 CT 5-15 1313C remaining C remaining during experimentduring experiment

4.5

5

5.5

6

0 10 20 30 40 50 60 70 80

time (d)

100+

ln13

C CT5-15block1

CT5-15block2

CT5-15block3

CT5-15block4

NT 0-5 NT 0-5 1313C remaining C remaining during experimentduring experiment

4.5

5

5.5

6

0 10 20 30 40 50 60 70 80

NT0-5block1

NT0-5block2

NT0-5block3

NT0-5block4

Residue Decomposition KineticsResidue Decomposition Kinetics

RapidRapid SlowSlow

---------k/day---------------------k/day------------

-0.0316-0.0316 -0.0024-0.0024

By T=5, no significant difference By T=5, no significant difference between tillage or depth in remaining between tillage or depth in remaining total amount of total amount of 1313C in soil:C in soil:

0-15 cm average 0-15 cm average 1313CC

----------------‰ (PDB)--------‰ (PDB)--------

CTCT +28.66+28.66

NTNT +34.63+34.63

ConclusionsConclusions

• 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

AcknowledgmentsAcknowledgments• Geronimo Watson, Karina Fabrizzi, Jamey Geronimo Watson, Karina Fabrizzi, Jamey

Duesterhaus, and undergraduate lab techsDuesterhaus, and undergraduate lab techs• Dr. Chuck RiceDr. Chuck Rice• Dr. Mary-Beth KirkhamDr. Mary-Beth Kirkham• Dr. Clenton OwensbyDr. Clenton Owensby• Dr. Dallas PedersonDr. Dallas PedersonThis material is based upon work supported by the Cooperative State This material is based upon work supported by the Cooperative State Research, Education, and Extension Service, U.S. Department of Research, Education, and Extension Service, U.S. Department of Agriculture, Under Agreement No. 2001-38700-11092.Agriculture, Under Agreement No. 2001-38700-11092.