Sources of variation in nitrous oxide flux from Amazonian ecosystems

Nitrous oxide flux and soil nutrient characteristics were measured in three undisturbed tropical ecosystem types, in cleared and burned areas, and in areas of forest converted to pasture near Manaus, Brazil. Nitrogen mineralization, nitrification, and soil nitrogen pools were high in upland forests on clay soils (terra firme) and low in the sand‐type and floodplain (varzea) soils. Nitrous oxide flux followed the same pattern, with an average flux of 1.9 ng cm −2 h −1 in terra firme, 0.3 in sand types, and 0.1 in varzea. Flux from recently cleared and burned areas did not differ from terra firme forest, but pastures had significantly elevated fluxes (10.3 ng cm −2 h −1 ). These data were combined with satellite data‐based areal estimates of land cover classes to estimate total N 2 O‐N flux from the intensive study area used by the Amazon Boundary Layer Experiment. Total N 2 O‐N flux from the area was 22.9 kg h −1 ; pastures covered 11% of the area but accounted for over 40% of the flux.