Organic Carbon and Formation of Soil Aggregates on Areas of Natural Vegetation Converted to Pasture in Southern Amazonas.

The objective was, therefore, to evaluate the impact on organic carbon and the formation of soil aggregates in areas of natural vegetation converted into pastures in southern Amazonas. The research was carried out in seven areas in the municipality of Humaitá, Amazonas, Brazil, five of which were pastureland, one native forest, and one natural field. Soil samples were collected at depths of 0–10 and 10–20 cm in the seven study areas and analyzed for aggregate stability, soil density, soil organic carbon, and the calculated soil organic carbon stock. Univariate, bivariate, and multivariate analyses were then carried out. Conversion from forest to pasture had a negative impact on percentage of aggregates >2 mm, soil density, concentration and stock of soil organic carbon. Organic carbon correlates positively with percentage of aggregates >2 mm, geometric mean diameter and weighted mean diameter, and negatively with soil density. Aggregate stability influences carbon sequestration in the pasture and forest areas studied, but has no influence in the natural grassland environment. [ABSTRACT FROM AUTHOR]