Nitrogen oxide emissions affected by organic fertilization in a non-irrigated Mediterranean barley field

Contradictory findings can be found in the literature regarding the effects of applying organic instead of mineral fertilizers on the associated emissions of nitrous oxide (N2O) and nitric oxide (NO). The main aim of this experiment was to study the effect on these emissions of applying mineral or organic fertilizers to a non-irrigated crop under Mediterranean conditions. A secondary aim was to determine whether application of the fertilizer had a residual effect on the N2O and NO pulses observed after the first rainfall events in autumn, and the magnitude of these fluxes. A field experiment was carried out with a barley crop (Hordeum vulgare L. cv Bornova). Untreated pig slurry (UPS), digested pig slurry (DPS), municipal solid waste (MSW) and composted crop residues mixed with sewage sludge (CCR + S) were applied to the soil. The resulting emissions were compared with those from a mineral fertilizer, urea (U), and a control treatment (C), in which no nitrogen was applied. Very low NO and N2O fluxes were measured during the entire experimental period in all treatments. The accumulated N2O emissions from the organic and inorganic fertilizers ranged from 266 to 345 g N2O-N ha−1 and did not show significant differences. Three of the four organic fertilizers had the positive effect of reducing NO emissions (28.82–44.48 g NO-N ha−1) compared with inorganic fertilizer (61.86 g NO-N ha−1). Nitrous oxide pulses were observed in autumn. Negative N2O fluxes were measured on several occasions. The emission factor relating N2O emissions to the N applied as fertilizer, ranged from 0.06 to 0.17% for MSW and DPS, respectively, which is much lower than the default factor proposed by the IPCC. The emission factor which relates N2O emissions to crop production ranged from 241 to 361 mg N2O-N kg−1 for DPS and U, respectively, suggesting that DPS should be promoted in order to reduce N2O emissions.