Notes
Slide Show
Outline
1
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
2
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
3
 
4
 
5
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
6
Materials and Methods
7
Ashland Experimental Farm, Manhattan, KS
  • 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).
8
Materials and Methods
9
 
10
Materials and Methods
11
Materials and Methods
12
Materials and Methods
13
Soil Chemical and Physical Parameters and 2004 Climate Data
14
Soil: Muir silt loam
15
2004 Precipitation
16
2004 Temperature
17
Results
18
Total Soil C – Tillage X Depth Interaction
19
Total Soil N – Tillage X Depth Interaction
20
CT 0-5 13C remaining during experiment
21
CT 5-15 13C remaining during experiment
22
NT 0-5 13C remaining during experiment
23
Residue Decomposition Kinetics
24
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
25
Acknowledgments
  • Geronimo Watson, Karina Fabrizzi, Jamey Duesterhaus, and undergraduate lab techs
  • Dr. Chuck Rice
  • Dr. Mary-Beth Kirkham
  • Dr. Clenton Owensby
  • Dr. Dallas Pederson
26
 
27