Light fraction of soil organic C (LFOC) represents a major portion of labile soil organic C (SOC) and is a key attribute of soil quality. Soil respiration (C min) is an important index depicting the potential activity of the labile SOC. Six field experiments, varying in duration (8 to 25 years), in location (brown [aridic Kastanozem], dark brown [typic Kastanozem] and black chernozemic soil zones of Saskatchewan, Canada; all soils were classified as Chernozems) and soil texture, were conducted to evaluate the impact of tillage and crop rotations on crop production and soil quality. We sampled the 0-7.5 cm depth of soil in these experiments to determine the treatment effects on LFOC, the proportion of LFOC in the SOC (LFOC:SOC) and C min. The crops in the rotation were spring wheat, flax, winter wheat, peas and rape. Increasing the frequency of summer fallow in cropping systems decreased the LFOC in all soil zones; it also decreased the proportion of LFOC in SOC and C min. Tillage had little impact on LFOC in the brown and dark brown chernozemic soil zones, although it significantly decreased LFOC in the black chernozemic soil zone. Thus, crop rotation had a greater impact on LFOC than tillage. Tillage did not influence C min in any soil zone. Because adoption of no-till management increased SOC in all soil zones, we concluded that LFOC was not a sensitive indicator of the impact of tillage on this soil quality attribute for these chernozemic soils in Saskatchewan. We also found that LFOC:SOC is directly proportional to sand content. This relationship may assist us in partitioning SOC pools with differing turnover times when modelling SOC dynamics.
