ORGANIC MATTER AND AGGREGATION OF A PLANOSOL UNDER DIFFERENT FOREST COVERINGS

Abstract

The litter quality can alter soil aggregation, modifying the transformation dynamics and allocation of soil carbon (C) in different compartments. This study evaluated the aggregate stability and its relation with litter chemical characteristics, organic carbon and free light fraction (FLL) from the organic matter under three different types of vegetation covering: secondary forest (FS) and plantings of Mimosa Caesalpiniaefolia (PM) and Carapa guianenses (PA) with subsequently natural regeneration. Litter samples were characterized using polyfenols, lignin, suberine, tannin and holocelulose content and C/N relationship. Soil samples were collected in two depths (0-10 and 10-20 cm) and soil aggregation were estimate using mean weight diameter (DMP), mean geometric diameter (DMG) and index of aggregate stability (IEA) analysis . Soil samples in the same depths were also characterized using C and FLL content. The highest suberine and polyfenols content of the litter found in the areas FS and PM reduced the speed of residues decomposition in the soil causing larger FLL content in both coverings. Those compositions contributed to the stabilization of C in the mineral phase, because the highest C content was found in those areas. This fact is confirmed by the values of DMP, DMG and IEA among the areas. They are higher in the coverings, PM and FS. It can be concluded that the polyfenols and suberine content were decisive in the subdivision of C and in the aggregation of the soil in the areas of FS and PM.