Con el propósito de determinar la influencia del cambio de uso de la tierra en el secuestro de carbono orgánico total (CO total) y la fracción de carbono orgánico pasivo (CO pasivo) en suelos, se realizó una investigación bajo pasturas mejoradas (Brachiaria brízantha) más árboles (PmA), pasturas degradadas (con especies nativas y naturalizadas) (Pd) y bosque secundario (Bs) a diferentes profundidades, en fincas ganaderas del sector San Miguel de Barranca, Puntarenas-Costa Rica. La precipitación media en el área de estudio fue de 2043 mm, temperatura promedio 27.2 °C y suelos Typic Rhodustalfs. Se utilizó un diseño irrestricto al azar en parcelas divididas con cinco repeticiones, donde la parcela grande fue el sistema y la parcela pequeña la profundidad. Las variables evaluadas fueron: densidad aparente (DA), pedregosidad, fertilidad, textura, CO total y CO pasivo en suelo, biomasa de raíces finas (BMRF), biomasa de pastos e inventario de especies arbóreas y arbustivas.A study was conducted to determine the influence of land use changes on total organic carbón sequestration and fractioning of passive organic carbón. The study was undertaken in three land use types on cattle farms situated in San Miguel de Barranca (Puntarenas, Costa Rica): improved pasture (Brachiaría brizantha) associated with trees, degraded pasture (with native and naturalized species) and secondary forest. Average precipitation in the area was 2043 mm and average temperature recorded was 27.2 °C during the period on the study. Soils in the study area were characterized as Typic Rhodustalfs. Sampling was conducted in plots under a random sampling regime with five repetitions, where the large plot was the system and the small plot the depth. The following soil variables were evaluated: buík density, soil fertility, texture, total soil organic carbón and passive organic carbón. Other variables that were studied included fine root biomass, pasture biomass, and an inventory of tree and shrub species.