EMISSIONS OF NITROUS OXIDE FROM ARABLE SOILS: EFFECTS OF TILLAGE REDUCED N INPUT AND CLIMATE CHANGE

Nitrous oxide (N2O) flux measurements from an Irish spring barley field managed under conventional and reduced tillage and different N fertilizer rates at the Teagasc Oak Park Research Centre were made for two consecutive seasons. The aims were to investigate the efficacy of reduced tillage, reduced N fertilizer and climate change on N2O fluxes and emission factors and to study the relationship between crop yield and N-induced fluxes of N2O. The soil is a sandy loam with a pH of 7.4 and organic carbon and nitrogen content at 15 cm of 19 and 1.9 g kg-1 dry soil, respectively. Three climate scenarios, a baseline of measured climatic data from a nearby weather station and a high and low temperature sensitive scenarios predicted by the Hadley Global Climate Model were investigated. The Field-DeNitrification DeComposition (DNDC) was tested against measured nitrous oxide flux from the field, and then used to estimate future fluxes. Reduced tillage had no significant effect on N2O fluxes from soils or crop grain yield. Soil moisture and soil nitrate are the main significant factors affecting N2O flux. The derived emission factor was 0.6% of the applied N fertilizer. By reducing the applied nitrogen fertilizer by 50 % compared to the normal field rate, N2O emissions could be reduced by 57% with no significant decrease on grain yield or quality. DNDC was found suitable to estimate N2O fluxes from Irish arable soils however, underestimated the flux by 24%. Under climate change, using the high temperature increase scenario, DNDC predicted an increase in N2O emissions from both conventional and reduced tillage, ranging from 58 to 88% depending upon N application rate. In contrast annual fluxes of N2O either decreased or increased slightly in the low temperature increase scenario relative to N application (-26 to +16%). Outputs from the model indicate that elevated temperature and precipitation increase N mineralisation and total denitrification leading to greater fluxes of N2O. Annual uncertainties due to the use of two different future climate scenarios were significantly high, ranging from 74 to 95% and from 71 to 90% for the conventional and reduced tillage respectively.