Dinâmica de nitrogênio em solos de florestas secundárias sob diferentes históricos de uso nos municípios de Santarém e Belterra, Amazônia Oriental

Abstract

If the nutrient cycling through decomposition of organic material and the economy of the use of nutrients by the vegetation are factors that enable the maintenance of a large part of the primary forests in the Amazon, it is predictable that both factors are affected before anthropogenic changes that modify the vegetation, in order to output nutrients that was contained above the soil biomass. This work aimed to determine changes in the dynamics of nitrogen nutrient in secondary forest soils with the following historical usage: logging, management and burns, as well as, clear cutting in Santarém and Belterra Cities, Eastern Amazon. Among the evaluated parameters are: efficiency in the use of nitrogen, C: N rate in litterfall and floor, nitrate and ammonium in the soil, nitrogen mineralization rates and analysis of the 15N isotope. There was a trend to more efficient in the use of nitrogen in management treatments and burning and clearcutting, which resulted in lower quality of the fresh litterfall and floor, as well as lower mineralization rates. The availability of nitrogen showed a tendency to be higher in primary and managed forests. As a measure of integrating character to the dynamics of N in the soil, the isotopic analysis indicated a reduced dynamic in forests subjected to clearcutting in relation to primary forest. It is proposed for the studied areas a conceptual model of recovery of the N dynamics in the soil, in which the secondary forests of this work are outing of the initial phase of limitation in N, and evolving into the primary forest standards.