Soil C Dynamics Following Addition of 13 C-labeled Grain Sorghum (Sorghum bicolor) Residue Paul White and Dr. Charles W. Rice Department of Agronomy Kansas State University Manhattan, KS

Carbon Sequestration Atmospheric CO 2 levels have increased from 260 to 370 ppmv (IPPC, 2004). Increasing soil C storage may assist in offsetting increases in CO 2 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 Biology CO 2 SunlightTemperatureMoistureNutrients Substrate Quality Inputs Outputs

Adapted from Paul and Clark, 1996 Readily decomposable Moderately decomposable Resistant Plant residue CO 2 Slow soil C Stable soil C CO 2 Microbial Biomass C Plant and microbial byproducts CO 2 INPUTS = OUTPUTS Temporal C changes in soil aggregates? Changes in microbial community dynamics?

Objectives During one growing season: Measure the mineralization of 13 C-labeled plant residue Measure the changes in soil TC and TN Measure the changes in soil TC and 13 C in macro- and microaggregates Determine microbial community changes in response to added residue

Materials and Methods

Ashland Experimental Farm, Manhattan, KS Continuous Sorghum under No- Tillage (NT) and Conventional Tillage (CT)Continuous Sorghum under No- Tillage (NT) and Conventional Tillage (CT) 4 Blocks4 Blocks 2 Residue Levels: Control (no residue) and 0.5% by weight2 Residue Levels: Control (no residue) and 0.5% by weight 7 Sample Times: 0, 3, 16, 25, 40, 68, and 159 d7 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).Data analyzed using SAS v9 Proc Mixed and means separated at the 5% significance level (SAS Institute, Cary N.C). Field Microcosm Experiment

Materials and Methods 0.5X Hoagland’s Pulse labeled 5X with 100% 13 CO 2 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 13 C (PDB) ----% ‰ Sorghum bicolor CV: Mycogen 1506

Anion and Cation Exchange Resin bag NT 2.1 g 13 C labeled residue placed on soil surface CT 2.1 g Mixed evenly with upper 15 cm soil with soil 15 cm 20 cm deep by 5 cm diameter PVC cores Materials and Methods

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. Sample Times: d

Total % C and N 13 C Whole Soil 13 C Aggregates (>1000  m,  m,  m, and  m) Phospholipid Fatty Acids Neutral Lipid Fatty Acids Temporal C changes in aggregates? Changes in microbial community structure? Overall system stability New input decomposition and retention C measurements on a scaled approach Materials and Methods

Total % soil C, N by dry combustion & TCD detection 13 C whole soil measured by conversion to CO 2 using dry combustion and isotopic 13 C measured using Europa IRMS. 13 C Data reported relative to the Pee Dee Belemnite ( % 13 C, or 0‰) Materials and Methods

Soil Chemical and Physical Parameters and 2004 Climate Data

Soil: Muir silt loam TillageDepth pH P Ca K Mg Na SO 4 -S NH 4 -N NO 3 -N TC TN 1: mg/kg %---- 1: mg/kg %---- CT CT NT NT Bulk Density: NT=1.40 g/cm 3 CT=1.36 g/cm 3 (G. Doyle, Ph.D. Dissertation) Data reported on a Mg/ha to 15 cm depth basis

2004 Precipitation Sample Times:

2004 Temperature 2004 Air Temperature Air Temp

Results

Total Soil C – Tillage X Depth Interaction MgC/ha CT NT Treatment Time=0 Soil C MgC/ha CT NT Treatment Time=1 Soil C MgC/ha CT NT Treatment Time=2 Soil C MgC/ha CT NT Treatment Time=3 Soil C MgC/ha CT NT Treatment Time=4 Soil C Treatment MgC/ha CT NT Time=5 Soil C MgC/ha CT NT Treatment Time=6 Soil C a a a b a a a b

MgN/ha CT NT Treatment Time=1 Soil N MgN/ha CT NT Treatment T=0 Soil N MgN/ha CT NT Treatment Time=2 Soil N MgN/ha CT NT Treatment Time=3 Soil N MgN/ha CT NT Treatment Time=4 Soil N MgN/ha CT NT Treatment Time=5 Soil N MgN/ha CT NT Treatment Time=6 Soil N Total Soil N – Tillage X Depth Interaction

CT C remaining during experiment Time (d) ln100+13C CT0-5block1 CT0-5block2 CT0-5block3 CT0-5block4 Kinetics modeled as first order having a rapid and slow phase according to: C t =C o -e kt

CT C remaining during experiment

NT C remaining during experiment

Residue Decomposition Kinetics RapidSlow k/day By T=5, no significant difference between tillage or depth in remaining total amount of 13 C in soil: 0-15 cm average 13 C ‰ (PDB) CT 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 13 C levels were not different between tillage regimes Label detectable throughout growing season 13 C Aggregate analysis and microbial lipids analysis may indicate management effects at a finer resolution

Acknowledgments Geronimo Watson, Karina Fabrizzi, Jamey Duesterhaus, and undergraduate lab techsGeronimo Watson, Karina Fabrizzi, Jamey Duesterhaus, 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 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