Atributos edáficos e qualidade do solo em áreas de agricultura, pastagem e fragmentos florestais na região do médio vale do Paraíba do Sul, Rio de Janeiro

Abstract

Changes in ground cover directly influence the soil physical and chemical attributes, and so the soil quality, fundamental to the development of sustainable agriculture.The objective of this study was to evaluate the influence of vegetation coverage and land usage on the edaphic attributes of areas of Inceptisols. The study was conducted in the Mid Paraíba do Sul Valley in Pinheiral municipality. There were chosen six areas: Secondary Forest of Advanced Stage (FSEA), Secondary Forest of Mid Stage (FSEM), Secondary Forest of Initial Stage (FSEI), Pasture with Mixed Management (PMM), Perennial Agriculture (AP), and Annual Agriculture (AA). The soil samples were taken at four depths (0-5, 5-10, 10-20 and 20-40cm) and two periods, in December 2009 (summer) and in August 2010 (winter). They were evaluated the physical properties: bulk density (BD), particle density (Dp), macro and microporosity, granulometry, total pore volume, aggregate stability through mean weight diameter (MWD) and mean geometric diameter (MGD), soil resistance to penetration; and usage of the georadar, computed tomography(CT) and X-ray techniques. The chemical analysis consisted of: pH, Mg, Ca, Al, K, Na, Al and H + Al and P, total organic carbon (TOC) and chemical fractionation of soil organic matter (SOM), quantifying the carbon in the humin fraction (C-HUM), humic acids (C-FAH) and fulvic acids (FAF-C). Regarding the physical properties, the sand-clay-loamy texture class was found in all areas and depths. The values of Ds varied according to vegetation coverage, where the AA and AP areas showed the highest values, and the other areas were very similar and smaller in the 0-5 cm depth at both periods. The values of DMP and DMG varied according to the DS in all areas, for the same depth. The usage of the georadar, associated to the soil resistance to penetration data, allowed to observe an increase in soil penetration resistance with depth, in the secondary forest of initial, intermediate and advanced stage, respectively, from 2.0 to 2.5 MPa, from 2.0 to 3.0 MPa, and from 2.5 to 6.0 MPa, due to the increase of roots with the successional stage. In the areas of PMM, AP and AA the increase in the soil penetration resistance was due to the presence of fragments of parent materials along the soil profile. The AA area, at a depth of 20-40 cm, also showed a reduction in soil penetration resistance due to presence of ant galleries. Computed tomography was an efficient tool, and it can be compared with the analysis of bulk density and porosity. The georadar data showed differences in the resistance to penetration of each area, depending on the soil coverage and use. The use of georadar associated with measurements of soil penetration resistance highlighted changes in soil properties in the different areas, and it is fast, non destructive and continuous in the transect, showing potential for pedological studies.