N2O emissions from spring barley production as influenced by fertilizer nitrogen rate

Usage of mineral nitrogen (N) fertilizers for agricultural crop production systems is a major contributor to anthropogenic nitrous oxide (N2O) emissions. As part of a national study to quantify N2O emissions under different cropping systems and in different eco-regions, this study quantified the effect of fertilizer N rate on spring barley (Hordeum vulgare L.) on N2O emissions in 3 yr in a cool maritime climate with humid soil moisture regimes. Treatments were 0, 75 and 150 kg N ha(-1) as ammonium nitrate applied as a pre-plant broadcast. N2O emissions were increased by fertilizer N application in each year. In 2003 and 2005, elevated N2O emissions occurred in the 6-wk period following fertilizer application when soil NO3-N concentrations were high. However, in 2004 and 2005, peak N2O emissions occurred near crop harvest. Elevated N2O emissions at this time were attributed to increased carbon availability due to re-wetting of dry soil. Therefore, the effect of fertilizer N management on N2O emissions may not necessarily occur immediately after treatment application. This emphasizes the importance of measuring N2O emissions outside of the crop growth period. Fertilizer-induced cumulative N2O emissions averaged 0.011 and 0.021 kg N kg(-1) N when fertilizer N rate was increased from 0 to 75 kg N ha(-1) and from 75 to 150 kg N ha(-1), respectively, indicating increased N2O emissions when fertilizer is applied at above optimal rates. N2O emissions increased linearly with nitrate intensity, the summation of daily NO3-N concentrations for 0- to 15-cm depth. This suggests that the non-linearity in the relationship between fertilizer N rate and N2O emissions can be explained by the decreasing efficiency in crop NO3-N uptake at high fertilizer N rates.