Soil Tillage Effects on the Contributions of Soil and Plant C Pools to CO2 Emissions.

Soil management practices such as tillage may impact CO₂ emissions in agricultural soils due to their effect on soil organic matter (SOM) components and dynamics. The objective of this study was to identify the carbon substrates contributing to CO₂ emissions, by measuring the δ¹³C of soil organic carbon pools and crop residue carbon inputs on conventional and no-tilled plots cropped in a rotation of C₃ (soybean - Glycine max L.; winter wheat - Triticum aestivum L.) and C₄ species (corn - Zea mays L.). Measurements were made of the organic carbon content and δ¹³C of total soil organic matter, plant residues and soil microbial biomass. A laboratory incubation was carried out to measure the δ¹³C of CO₂ derived from microbial respiration. Density separation followed by acid hydrolysis was employed to separate the SOM pools into light, heavy and recalcitrant fractions.  Integration and validation of experimental results will be carried out using the DAYCENT soil-plant ecosystem model.  The expected output of this research includes a better understanding of CO₂ fluxes due to agricultural activities and soil biophysical processes; with the potential for identifying management strategies for minimizing emissions.