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Copyright of Brazilian Journal of Agricultural Sciences / Revista Brasileira de Ciências Agrárias is the property of Universidade Federal Rural de Pernambuco and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Agrociencia is the property of Colegio de Postgraduados and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The objective of this study was to evaluate the total organic carbon and the physical and chemical fractions of organic matter in an Alfisol under different use systems. The land use systems evaluated was homogeneous forestry of Eucalyptus grandis. agrosilvopastoral system and native grassland, in layers from 0.000-0.025 and 0.025-0.075m depth. The coarse fraction (CFG) and the carbon associated minerals (CAM) were obtained by physical fractionation. The free light fraction (FLL), light occluded (FLO) and heavy (FP) were obtained by densimetric physical fractionation. The non-humicfractions (NH), fulvic acid (AF), humic acid (HA) and liumin (HU) were obtained by chemical fractionation. The Eucalyptus grandis system promoted higher total organic carbon, CFG, FLL and FLO and AF. In the surface layer, the protective recalcitrance mechanisms by organic matter molecular and chemical stabilization are overlapping stability which result from aggregates occlusion. As is difficult to form aggregates due to sandy soil matrix, carbon youth which enter the system is decomposed by microorganisms going to a more advanced stage of decomposition, forming in this case associations with silt and clay particles. This occurs in soils where the clay percentage is low. Through the fractionation it was observed that most of the soil organic matter is stored in the form of HU. [ABSTRACT FROM AUTHOR]