Recovery of total organic carbon and humic fractions of the soil organic matter in different land uses

The objective of this study was to quantify the total organic carbon (COT) and the C content of humic fractions (humic-CHUM, humic acid-CFAH and fulvic acid-CFAF) of organic matter at depths of 0-0.05, 0.05-0.10 and 0.10-0.20 m in different stages of an area under slash-and-burn agriculture (slash-and-burn 2 years old, 10 and 15 years old fallow), in the agroforestry system (AFS), in the eucalyptus plantation and in the native forest. TOC levels were lower in the slash-and-burn 2 years old than in the native forest, and higher in relation to the slash-and-burn with 10 years of fallow (0.0-0.05 and 0.10-0.20 m). The biomass burning in the slash-and-burn 2 years old increased the CHUM in relation to the 10 years old fallow (0.0-0.10 m) and the AFS (0.05-0.10 m). Burning also increased the CFAF and decreased CFAH in the slash-and-burn 2 years old in relation to fallow (10 and 15 years), SAF and eucalyptus. A fallow period as long as 15 years is long enough to restore the TOC, CHUM and CFAH of the soil to a condition similar to the soil under native forest, AFS and eucalyptus.