Chemical and physical fractions of soil organic carbon in a forest soil currently under different uses

Organic matter may be considered an important soil quality indicator, as it is related with many soil chemical, physical, and biological characteristics. The study of total organic carbon (TOC) of the soil and its fractions is important. This study was conducted in a micro basin, with the purpose of. analyzing characteristics and quantify the stocks of total organic carbon (TOC) and its fractions as evidence of soil quality after different forms of use: (1) Atlantic Forest, (2) Cocoa (Theobroma cacao), and (3) Pasture (Brachiaria decumbens). Samples were collected for each use type (at 0-10 and 10-20 cm). The chemical and physical soil properties were characterized and the chemical and physical fractions of organic carbon determined. It was observed that the organic carbon levels did not differ in the two depths analyzed, even under different use types. The percentage of humified carbon in the fulvic acid and humin fractions was higher in the 0-10 cm layer under pasture and the percentage of non-humified carbon was lower under cocoa and pasture. There was a higher C:N ratio in the 10-20 cm layer of the soil underpasture. Cocoa acao increased the level of organic carbon in the light fraction in the 10-20 cm layer. The substitution of the native forest by cocoa and pasture resulted led to no significant changes in the COT concentration and organic matter fractions in the studied area.