Abstract
Oxisols have great ecological significance in tropical soils because they are the dominant soil type of the Brazilian Amazon ecosystem, comprising more than 40% of its total. To estimate carbon (C) stocks and changes requires knowledge of the vertical distribution of C in profiles. The objective of this study was to determine if specific patterns occur in C profiles of Oxisols in the Western Brazilian Amazon so that total C storage can be assessed down to any given depth by simple models with low input data requirements. Two models, a power-based model and an exponential-based model, were tested using nonlinear regression analysis on a soil database made up of 129 Oxisol profiles corresponding to 519 soil horizons. These models, as judged by the coefficient of determination (R 2 ) value, explained more than 55% of the total variance for all of the horizons, whether or not segregated by taxonomic unit. The models were then tested with individual profiles. The power model exhibited a tendency to overestimate C stocks when integration was done for the 0-20-cm and the 0-100-cm layers. Results from the exponential model were better than those from the power model. The R 2 values were greater than 0.82, and the associated standard error was reduced. In a validation procedure, the mean error (ME) was close to zero for the exponential model, with a systematic ME of only 0.06 kg C.m -2 for the 0-100-cm layer.
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