This project represents additional effort for completion and extension of current N2O and NO flux from tropical pastures and forests. The objectives of the project are: 1). to measure, over an annual cycle, N2O and NO flux from common land use types in lowland tropical Costa Rica representing a typical cycle of land usage: primary forests, active pastures created from these forests, abandoned pastures and secondary forests derived from abandoned pastures, and 2). to combine field experiments with the field measurements in objective 1 for determination of the importance of factors controlling the rates of these fluxes. For the additional period of research the project team will 1). complete the annual cycle on the land use plots, 2). make exploratory measurements of flux rates from other soil and land use types in the area to extend the ability to generalize results, and 3). carry out laboratory and field experiments that have been stimulated by earlier our findings. These experiments include rain storm simulations in forest sites to determination the causes for short-term time dynamics in gas flux from these systems, and fertilization experiments in pasture sites to determine the causes for lower rates of nitrogen oxide emissions in those systems compared with the forests.
