Pasture-agroforestry systems have become an important strategy for the use of sandy soils in the Pampa Biome. The purpose of this study was to evaluate the aggregation, total organic C (TOC) and total nitrogen (TN), carbon of the physical fractions and humification degree of organic matter (OM). Evaluations were conducted in an Alfisol under homogenous eucalyptus forest (HF), between the rows of a pasture-agroforestry system (PA) and in native pasture (NP) in the layers 0.000-0.025, 0.025-0.075, 0.075-0.125, and 0.125-0.225 m. Disturbed samples were collected to evaluate water-stable aggregates (WSA %), TOC and TN. The physical (granulometrical and densimetrical) fractionation of OM was carried out, and the free light fraction (FLF) and occluded light fraction (OLF) of OM in the surface layer subjected to Fourier Transform Infrared (FTIR) and Electron Paramagnetic Resonance (EPR) analyses. The WSA and mean weight diameter in the layer 0.025-0.075 m indicated a greater degradation of the PA soil. Higher levels of TOC, TN, coarse fraction carbon (CFC), carbon associated with minerals (CAM), FLF and OLF in the surface layer were observed in HF. Between land uses, the FTIR spectra were similar. However, the FLF had more intense bands in the region of 1072 cm-1, suggesting higher amounts of polysaccharides than in the OLF. The spin densities obtained by EPR at OLF were higher than of FLF, indicating a higher humus fraction.
eucalyptus; physical fractionation; sandy soils
