Publicação on-line; 36 ref.; 2 tables; 3 illus.; Summary (En)

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.