Soil N dynamics and water content are important controls of nitrous (N2O) and nitric (NO) oxide emissions from tropical soils. We used a chronosequence of one forest and six pastures to investigate how soil N availability and soil moisture content affect emissions of N2O and NO. Forest soils had high N availability and large N oxide emissions. Forest conversion to pasture decreased N availability and N oxide emissions. In the forest where N availability was high, seasonal changes in soils moisture led to higher N2O fluxes during the wet season, but higher NO fluxes during the dry season. Soil water content exerted the largest control on N2O emissions, which seemed to be determined by a threshold value of approximately 29--30%, below which N2O emissions were nearly constant and above which they increased (Figure 5a). In pastures, where low N availability constrains N2O and NO fluxes, soil water content has a minor influence on N oxide emissions. ¿ 2001 American Geophysical Union