SOIL CARBON-DIOXIDE FLUXES FROM CONVENTIONAL AND NO-TILLAGE SMALL-GRAIN CROPPING SYSTEMS

Conversion to conservation tillage systems increases soil C content by reducing soil erosion and the rate of organic matter oxidation, We hy pothesized that these effects could impact soil emission of CO2, This study (i) determined if CO2 emissions were reduced in the first years after conversion to no-tillage (NT) relative to conventional tillage ( CT), (ii) evaluated whether differences in soil CO2 emissions between tillage treatments were related to soil temperature differences, and ( iii) determined if soil CO2 emission measurements provided an early es timate of soil management practice impact on soil organic C, In 1992 a nd 1993, CT and NT plots were planted to small-grain cereals in Ottawa , Ontario, on a Dalhousie silt loam (mixed, mesic, Typic Endoaquoll). Fluxes were measured using closed chambers connected to a portable CO2 analyzer, During growing season 1992, the CO2 emissions varied from 0 .05 to 0.18 mg CO2 m(-2) s(-1) with an average of 0.12 mg CO2 m(-2) s( -1) for CT and of 0.10 mg CO2 m(-2) s(-1) for NT. In 1993, the CO2 emi ssions varied from 0.06 to 0.35 mg CO2 m(-2) s(-1) with an average of 0.15 mg CO2 m(-2) s(-1) in both tillage treatments, Differences in soi l CO2 fluxes between treatments were related to differences in soil te mperature (r(2) = 0.62), giving an estimate of 75 g C m(-2) yr(-1) dif ference in organic C transfers to the atmosphere between CT and NT. Th ese results were validated using an independent estimation derived fro m long-term field experiments, Thus, soil CO2 flux measurements using dynamic closed chambers can provide early estimates of soil management impacts on soil organic C.