The objective of this study was to evaluate the distribution pattern of total organic carbon (TOC) and total nitrogen (TN) in the native field soil profile and Eucalyptus sp. The study was carried out in native field and in eucalyptus plantations with 20, 44, 180 and 240 months, located in Santa Maria and Manoel Viana, RS, Brazil. The decay rate (k) of the TOC and TN contents up to 1.2 m depth was determined by the graphical, numerical and mathematical method using the third order negative exponential model. The content of TOC and TN deep in the soil showed a third order negative exponential distribution. However, the methods used to estimate the decay rate generate differences in TOC and TN contents along the soil profile.
