Nitrous oxide emissions from an Uruguayan argiudoll under different tillage and rotation treatments

Lack of local data limits estimation of nitrous oxide (N2O) emissions from different land uses of Uruguay. As a first step towards obtaining local information, we measured from August 2003 to September 2004 N2O fluxes from a rotation-by-tillage experiment established in 1993 and from a nearby natural pasture (NP). Nitrous oxide emission rates were measured on an event-driven basis by using the closed chamber technique with six replicates per treatment. Fluxes varied considerably with time and the higher rates (more than 30 g N ha−1 day−1) were generally associated with periods of high soil water content, high temperature, and/or decreasing soil nitrate. We could not identify, however, any statistically significant correlation between flux and these variables. Throughout the evaluation period, fluxes from crops or cultivated pastures tended to be higher than those from NP, but the effects of tillage (no-till and conventional tillage) or rotation (continuous tillage and rotation with pasture) were not consistent. The application of 112 kg N ha−1 to barley did not increase N2O fluxes probably due to a high fertilizer use efficiency caused by the recommended three-split application and by the lack of rain during this period. The annual cumulative flows of different treatments compared well with those estimated using IPCC methodology, but the high spatial and temporal variability observed in this one-year study indicate that further research is needed to obtain reliable data on N2O fluxes from agricultural soils of Uruguay.