Comparison of N losses (NO3-, N2O, NO) from surface applied, injected or amended (DCD) pig slurry of an irrigated soil in a Mediterranean climate

Nitrous oxide (N2O), nitric oxide (NO), denitrification losses and NO3 leaching from an irrigated sward were quantified under Mediterranean conditions. The effect of injected pig slurry (IPS) with and without the nitrification inhibitor dicyandiamide (DCD) was evaluated and also compared with that of a surface pig slurry application (SPS) and a control treatment (Control) without fertiliser. After application, fluxes of NO and N2O peaked from SPS (3.06 mg NO-N m(-2) d(-1) and 108 mg N2O-N m(-2) d(-1)) and IPS (3.50 mg NO-N m(-2) d(-1) and 105 mg N2O-N m(-2) d(-1)). However, when irrigation was applied, N2O and NO emissions declined. The total N2O and denitrification losses were slightly large from IPS than from SPS, although the differences were not significant (P < 0.05). Emission of NO was not affected by the method of pig slurry application. DCD inhibited nitrification during the first 20-30 days and reduced N2O and NO emissions from pig slurry by at least 46% and 37%, respectively. Considering the 215 days following pig slurry application, the emission factor of N2O based on N fertiliser was 1.60% (SPS), 2.95% (IPS), and 0.50% (IPS + DCD). The emission factor for NO was 0.14% (SPS), 0.12% (IPS), and 0.02% (IPS + DCD). Environmental conditions of the crop favoured the denitrification process as the most important source of N2O during the experimental period. The differences in the denitrification rate between treatments could be explained by the pattern of water soluble carbon (WSC), that was the highest value in injected pig slurry (with and without DCD). Due to low drainage (5% of water applied), leaching losses of NO3 were lower than those of denitrification from the upper soil layer (0-10 cm) in all treatments and especially with IPS + DCD, where the nitrification inhibitor was very efficient in reducing leaching losses.