【Objective】 In this study, soil microbial activity and biomass carbon under 13-year conservation tillage(no-till)were assessed in a black soil agro-ecosystem in northeast China in order to determine the effect of tillage treatment on soil organic carbon and soil microbial biomass, which would provide a theoretical basis for valuing the ‘sink' or ‘source' function of soil carbon pool. 【Method】 The present study was conducted as part of a long term tillage experiment on the continuous maize(Zea mays L.),tilla...