Fontana, Ademir creator Pereira, Marcos Gervasio creator Balieiro, Fabiano de Carvalho creator Chagas, Cesar da Silva creator Donagemma, Guilherme Kangussu creator Oliveira, Lucienne Silva de creator text periodical abstract or summary bl. continuing eng ABSTRACT Soils with high organic carbon content, such as those with “humic A horizon”, occur in different regions of Brazil. This study aimed to determine the quantitative and qualitative characteristics of organic matter regarding the humic A horizon under different land uses in Bom Jardim, in Rio de Janeiro State, Brazil. Samples from forest, pasture, Eucalyptus plantation, coffee cultivation, olericulture, and also passion fruit soils were sampled and analyzed. In October 2011, undisturbed samples from humic A horizons, were collected for soil density analysis. In addition, disturbed samples were collected for the determination of organic carbon (Corg) content, total carbon, humic substance fractions contents and natural abundance of 13Carbon (δ13C). Low Corg contents were observed in areas under olericulture, pasture and passion fruit cultivation. The fulvic acid fraction was higher than other fractions, regardless of land use. The small variability in δ13C indicated maintenance of original Corg and suggest high resistance of Soil Organic Matter in humic A horizons. Keywords: organic carbon, humic substances, isotopic composition. Publicação on-line; 36 ref.; 2 tables; 3 illus.; Summary (En) SOLO CARBONO COMPOSIÇÃO QUÍMICA ISÓTOPO MATÉRIA ORGÂNICA Rio de Janeiro-RJ Instituto de Florestas - UFRRJ 1994 2025-0455 1415-0980 / ISSN 2179-8087 0nline BR2026001224 v. 27(1) p. 1-9; (2020) https://www.scielo.br/j/floram/a/vSDStL9B9cWqvmH6yvFpGRM/?format=pdf&lang=en https://www.scielo.br/j/floram/a/vSDStL9B9cWqvmH6yvFpGRM/?format=pdf&lang=en BR-BrBNA 260512 20260512150044.0 eng