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.