ORGANIC MATTER IN AREAS UNDER SECONDARY FORESTS AND PASTURE

Abstract

The objective of this work was to evaluate the soil carbon density and stock (EstC), the chemical and granulometric fractions of the organic matter and the isotopic signal of the soil δ¹³C in forest fragments and a mixed pasture area (MMP). The study was carried out in the municipality of Pinheiral, State of Rio de Janeiro. The evaluated areas were: fragment of secondary forest in initial stage (SFIS) with 20 years of regeneration; Fragment of secondary forest in intermediate stage (SFINS), with 25 years of regeneration; Advanced secondary forest fragment (SFAS) with 60 years of regeneration and mixed pasture (MMP). The attributes related to soil carbon showed significant responses to the effects of land degradation / recovery processes, especially for the following indicators: total organic carbon, organic matter stock and particulate organic matter. No significant alterations for humic substances, and prevalence of the humin fraction was found. The most significant changes in d¹³C values occurred up to the depth of 60 cm. In the grassland area, at 0-10 cm, 67% of the carbon stock comes from C₄ plants, reducing in the subsequent layers. In SFINS and SFAS areas, at 0-10 cm, the contribution of C₃ plants was significant, with minor changes in depth.