The influence of tillage on NO and N2O fluxes under spring and winter barley

Abstract. There is a lack of information about the influence of tillage and time of sowing on N₂O and NO emission in cereal production. Both factors influence crop growth and soil conditions and thereby can affect trace gas emissions from soils. We measured fluxes of NO and N₂O in a tillage experiment where grassland on clay loam soil was converted to arable by either direct drilling or ploughing to 30 cm depth. We made measurements in spring for 20 days after fertilizer application to spring-sown and to winter-sown barley. Both were the second barley crop after grass. Direct drilling enhanced N₂O emission primarily as a result of restricted gas diffusivity causing poor aeration after rainfall. Deep ploughing enhanced NO emission, because of the large air-filled porosity in the topsoil. NO and N₂O emissions were smaller from winter sown crops than from spring sown crops.   The three rates of N fertilizer application (40, 80 or 120 kg N ha^–1) did not produce the expected linear response in either soil available N concentrations or in NO and N₂O fluxes. We attributed this to the lack of rainfall in the ten-day period after fertilizer application and therefore very slow incorporation and movement of fertilizer into and through the soil.