Carbon isotope signature of soil respiration from agricultural fields: late fall and spring measurements in Ontario, Canada

Measurements of the isotopic signature of CO₂ fluxes from conventional and no-till areas were carried out during fall 2005 to spring 2006, and will be on-going over fall 2007 to spring 2008, in Ontario, Canada. Concentrations of ¹²C- and ¹³C-CO₂ isotopes were measured using a tunable diode laser trace gas analyzer. The d¹³C of soil respiration was then used to compare the proportion of C originating from crop residue (corn, a C4 plant) vs. soil organic matter (formed predominantly from C3 plants), in no-till and conventional plots. Results from 2005/2006 indicate more rapid decomposition of the ‘newly-added' residue in the conventional tillage treatment, with a stronger C4 signature (-16.7 ± 2.5‰) compared to the no-till field (-20.2±2.7‰). These results will be compared to recent measurements at the same site.