Abstract: The objective of this study was to evaluate the organic carbon (OC) distribution and inorganic phosphorus (P) fractions on different soil aggregates classes under forestry fragment of Atlantic Forest, pasture and agroforestry managed for a long period. Soil samples were collected at depths of 0.00-0.10, 0.10-0.20 and 0.20-0.60 m, and the aggregate stability analysis was performed at each depth. The OC and the inorganic P fractions (Pbic readily available, NaHCO3 0.5 mol L-1; PNa1 moderately available, NaOH 0.1 mol L-1; and PNa2 restricted availability, NaOH 0.5 mol L-1) were determined in the respective classes of soil aggregates 4-2, 2-1, 1-0.5, 0.5-0.25 mm. Soil under forestry fragment showed higher OC contents and regardless the land use, highest values of inorganic P were found in the aggregates > 1 mm. Forestry showed highest levels of Pbic, while agroforestry showed the highest levels of PNa1, and pasture had highest values of PNa2.

ABSTRACT Organic acids present in organic matter and, or, exudates by microorganisms and plants can increase the liberation of potassium present in minerals. The objective of this study was to characterize the residue from ornamental rocks and evaluate the release of K from these residues after the application of organic acids. The experiment was conducted under laboratory conditions and followed a 2 × 3 × 5 factorial design with three replicates. The studied factors were: two organic acids (citric acid and malic acid), three ornamental rock residues (R1, R2 and R3) and five organic acid rates (0, 5, 10, 20 and 40 mmol L-1). After agitation, K concentrations were determined in the equilibrium solution. Successive extractions were performed (1, 5, 10, 15, 30 and 60 days after the start of the experiment). The organic acids used (citric and malic) promoted the release of up to 4.86 and 4.34 % of the total K contained in the residue, respectively, reinforcing the role of organic acids in the weathering of minerals and in providing K to the soil. The K quantities were, on average, 6.1 % higher when extracted with citric acid compared to malic acid.