In an intercropping lettuce-carrot system submitted to crescent dosages of organic compost (0; 12; 24; 48 Mg ha-1) were monitored carbon from soil microbial biomass (MBC), labile carbon in fumigated soil (LCF), in non-fumigated soil (LCNF), in autoclaved soil (LCA) and total organic carbon (TOC) at 0-10 cm of depth. Pasture and forest areas surrounding the experiment were used as reference. Five samples from soil were evaluated at 8 days before the beginning of the experiment, 0; 6; 60 and 114 days after manuring (dam). LCF was the attribute that presented the most consistent correlation with TOC that is usually utilized to detect changes in soil organic matter. Increasing dosages of organic compost caused the increase of MBC, LCF, LCNF, LCA and TOC. From 60 days after planting and forward, MBC and LCF presented decrease of their levels according to the quality of organic compost. Pasture and forest soils behave as contrasts, holding lower and higher content of carbon of soil, respectively
