Nitrogen availability and leaching during the terrestrial phase in a v rzea forest of the Central Amazon floodplain

Availability and leaching of dissolved inorganic N (DIN = NH4 + NO3) in soil were measured in a periodically flooded forest of the Central Amazon floodplain (v rzea) during one terrestrial phase. Special emphasis was on the effects of a legume and a nonlegume tree species. NH4-N accounted for more than 85% of DIN even at the end of the terrestrial phase although it decreased throughout the experimental period. While extractable NO3 -N was always low in the soil (less than 15% of DIN), the amount of leached NO3 -N was in the same range as NH4-N. Under the legume trees mean DIN contents of the topsoil were higher than under the non-legume trees. DIN leaching from the topsoil (0– 20 cm) was significantly higher under the legume trees than at the other sites, also indicating a higher N availability. Therefore, despite considerable leaching legume trees may be an important source of N supporting a high biomass production of the v rzea forest.