Funds are provided to study nitrogen (N) cycles in the Brazilian Amazon. The research aims at quantifying N transformation and transport pathways in natural and agricultural settings in the Neotropics. The shift in agriculture combined with the increase in nitrogen fertilizer inputs in tropical regions have the potential to drive profound losses of nitrous oxide to the atmosphere, or increased movement of soluble N to rivers and streams. The proposed field research will quantify N2O fluxes and N fate in the vadose zone, groundwater and streams under natural conditions (tropical forest), single cropping of soybeans, and double cropping with soybeans and maize. Remote sensing will be used to scale up results from the field and model to the Amazon region, and incorporation of research results into a dynamic vegetation model (IBIS) that has been parameterized for the Amazon and will be used to estimate N emissions under different climate and land use management scenarios in the future. The work will test two hypotheses: (1) that increased N fertilization will lead to moderately but not greatly higher N2O emissions compared to natural forest because soils are well-drained and are not expected to go anaerobic long enough for accumulation of N2O, and (2) that N losses to streams will be minimal in N-fertilized plots because of high rates of uptake by maize crop and retention of any residual N leachates in deep, clay soils through anion exchange.
The research will aid in understanding effects of changing agricultural practices on greenhouse gas emissions and stream pollution in the Amazon. Partnerships with local Brazilian scientists and training of US and Brazilian students will be important impacts from the research. Public outreach and broad dissemination of results will be achieved through regular presentations to agricultural producers and policy makers in Brazil through established contacts, as well as the support of a US journalist to visit the research field sites, which are locations of long-term ecological and biogeochemical research.
