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Carbon stock variability and aggregate stability in soils of Amazon, Brazil

Converting natural ecosystems into agro-ecosystems often reduces soil organic carbon content by decreasing carbon input, as well as by increasing erosion losses and organic matter decomposition rate. This study aimed at evaluating carbon stocks, soil aggregate stability, and spatial variability of some other attributes in soils of Southern Amazonas state. The study was carried out on areas with archaeological dark earth (ADE), under rainforest, pasture, agroforestry environments, sugarcane, and cassava. We collected disturbed and undisturbed soil samples from 64 points in a regular spacing of 10 m at 0.0-10 cm depth. From these samples, we determined the stock of organic carbon (STOC), organic carbon (OC), organic matter (OM) content, soil aggregate stability (SAS), and soil bulk density (SBD). Data analysis included univariate, multivariate, and descriptive statistics. The STOC was higher in ADEs and the adjusted semivariograms pointed out a greater spatial variability for soils under pasture and cassava crop. Kriging maps of principal component analysis scores proved a positive correlation between the studied variables and terrain slope, with higher values for lower lands.