Emissions of nitrous oxide from Irish arable soils: effects of tillage and reduced N input

Nitrous oxide (N2O) flux measurements from an Irish spring barley field managed under conventional and reduced tillage and different N fertilizer applications at the Teagasc Oak Park Research Centre were made for two consecutive seasons. The aim was to investigate the efficacy of reduced tillage and reduced N fertilizer on seasonal fluxes and emission factors of N2O and to study the relationship between crop yield and N-induced fluxes of N2O. The soil is classified as a sandy loam with a pH of 7.4 and a mean organic carbon and nitrogen content at 15 cm of 19 and 1.9 g kg−1 dry soil, respectively. Reduced tillage had no significant effect on N2O fluxes from soils or crop grain yield. Multiple regression analysis revealed that soil moisture and an interaction between 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, approximately 50% of the IPCC default EF of 1.25% used by the Irish EPA to estimate GHG or the IPCC revised EF of 0.9%. This resulted in huge overestimations of 2,275 and 1,050 tonnes of N2O-N for using the old and revised IPCC default factors respectively. 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. This was consistent over the 2 years of measurements.