Nitrous oxide emissions as influenced by amendment of plant residues with different C:N ratios

To investigate the influence of plant residues decomposition on N2O emission, laboratory incubations were carried out for a period of 21 days using urea and five plant residues with a wide range of C:N ratios from 8 to 118. Incorporation of plant residues enhanced N2O and CO2 emissions. The two gas fluxes were significantly correlated (R2=0.775, p<0.001). Cumulative emissions of N2O and CO2 were negatively correlated with the C:N ratio in plant residues (R2=0.783 and 0.986 for N2O, and 0.854 for CO2, respectively). A negative relationship between the N2O–N/NO3−–N ratio and the C:N ratio was observed (R2=0.867) when residue plus urea was added. We calculated the changes in dissolved organic C (DOC) and the relevant changes in N2O emission. The incorporation of residues increased DOC when compared with the control, while the incorporation of residue plus urea decreased DOC. Cumulative emissions of N2O and CO2 were positively correlated with DOC concentration measured at the end of the incubation. In addition, the N2O emission fraction, defined as N2O–N emissions per unit N input, was not found to be a constant for either residue-N or urea-N amendment but dependent on C:N ratio when plant residue was incorporated.