Distribution of Organic Carbon in the Humic Fractions of Diagnostic Horizons from Brazilian Soils
2008
Fontana, A. | Pereira, M.G. | Anjos, L.H.C dos | Benites, V. de M.
This study was developed on 52 soil profiles, 61 surface diagnostic horizons, and 26 subsurface diagnostic horizons classified according to the Soil Taxonomy and Brazilian Soil Classification System (SiBCS) as Mollisols (Chernossolos), Spodosols (Espodossolos), Entisols (Gleissolos), Oxisols (Latossolos), and Histosols (Organossolos). The objective was to quantify the carbon (C) in organic matter fractions and to correlate it with soil chemical attributes. Soil organic matter was fractionated into fulvic acids (C-FAF), humic acids (C-HAF), and humin (C-HUM), and the ratios C-HAF/C-FAF and AE (alkaline extract)/C-HUM were calculated. Humin was the predominant fraction in Mollisols and Oxisols, which showed values of AE/C-HUM and C-HAF/C-FAF lower than 1.0. The humin fraction was also predominant in surface horizons of Spodosols and Entisols, whereas a higher content of C-FAF and C-FAH was observed in the subsurface horizons, with values higher than 1.5 for the AE/C-HUM ratio. C-HAF was predominant in the Histosols, and C-HAF/C-FAF ratio values were higher than 2.0. The highest correlation values with soil attributes were observed for C-HAF, C-HUM, and total organic C with pH, sum of bases, and cation exchange capacity. The differences in humic substances distribution was a useful parameter to characterize soil orders in the Brazilian soil classification system and to understand pedogenic processes.
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