Microbial biomass carbon and organic carbon were measured in a long-term field experiment (20 years) in Planaltina, DF, Brazil, under corn-soybean crop rotation. Six management systems were selected: disk plow before planting (ADPP); disk plow after harvesting (ADPC), no-till after disk plowing in the first year (PDAD); moldboard plow before planting (AVPP); moldboard plow after harvesting (AVPC), no-till after moldboard plowing in the first year (PDAV) and an undisturbed area of Savanna type vegetation, Cerrado (CE) as a reference. Soil samples were collected five times a year: 1- April, at soybean harvesting; 2- May, after soybean harvesting; 3- August, in the dry season with no crop on the field; 4- November, in the beginning rainfall season, at corn planting; 5- February, at corn tasseling. The samples were taken from five depths: 0-5, 5-10, 10-20, 20-30 and 30-40 cm of a clayey Red Latosol (Oxisol). Considering the whole study period, soil microbial carbon (Cmic) and soil organic carbon (Csoil) concentration were lower as soil profile depth increased for all management systems as well as in the Cerrado. Cmic and Csoil decreases under no-till system from superficial layers to the deeper ones were more pronounced than in the conventional systems. In the Cerrado, the microbial biomass represented a higher percentage of the total soil organic carbon in comparison to the management systems; there was no difference between conventional and no-till systems.
organic carbon; disk plow; moldboard plow; no-till; Latosol; Savanna
