01963naa a2200277 a 450000100080000000500110000800800410001902400520006010000160011224501410012826000090026952010990027865000210137765000240139865000120142265000140143465300220144865300280147065300260149870000190152470000230154370000210156670000210158770000220160877300550163021217752020-07-29       2020    bl uuuu     u00u1 u    #d7 ahttp://dx.doi.org/10.1590/2179-8087.0091192DOI1 aFONTANA, A.  aResistance of soil organic matter in "humic A horizons" of the mountainous region in the state of Rio de Janeiro.h[electronic resource]  c2020  aSoils 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 (C-org) content, total carbon, humic substance fractions contents and natural abundance of (13)Carbon (delta C-13). Low C-org 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 delta C-13 indicated maintenance of original C-org and suggest high resistance of Soil Organic Matter in humic A horizons.  aHumic substances  aSoil organic carbon  aCarbono  aHorizonte  aCarbono orgânico  aComposição isotópica  aSubstâncias húmicas1 aPEREIRA, M. G.1 aBALIEIRO, F. de C.1 aCHAGAS, C. da S.1 aDONAGEMMA, G. K.1 aOLIVEIRA, L. S de  tFloresta e Ambientegv. 27, n. 1, e20190091, 2020.