Nitrogen Dynamics in Hydrological Flow Paths of a Small Tropical Pasture Catchment

• Organic nitrogen dominated all hydrological flow paths.
• Surface runoff is not an important flow path for N movement.
• Pastures in the Atlantic Forest region are net sinks for N.

In this paper we report nitrogen (N) dynamics within hydrological flow paths of a small tropical pasture catchment within the Atlantic Rainforest region in Natividade da Serra, São Paulo State, Brazil. By collecting soil solution through 27 tension lysimeters, surface runoff through 9 plots, groundwater through one well and one stream over the course of a year, N species concentration and fluxes could be clarified. All hydrological flow paths were dominated by organic N (~ 60–85%). This finding is explained as a consequence of a drop of soil N cycling rates and N gaseous fluxes previously reported in the literature. Nitrogen input via bulk precipitation (~ 3.5 kg N ha− 1 year− 1) exceeded N hydrological output through stream water (~ 2 kg N ha− 1 year− 1). Similar findings have been described for pastures of the Brazilian Amazon Basin. If pastures like these are maintained without fertilization, catchments whose land use is old pastures may not be an important direct source of inorganic N for downstream regions.