Effects of fertiliser type and the presence or absence of plants on nitrous oxide emissions from irrigated soils

Nitrous oxide (N₂O) emissions and denitrification losses from an irrigated sandy loam soil amended with composted municipal solid waste (MSW), sheep manure (SM), surface applied pig slurry (SPS), incorporated pig slurry (IPS) or urea (U) were studied under Mediterranean conditions. We quantified emissions, in both the presence and absence of maize and N₂O production, via denitrification and nitrification pathways using varying concentrations of acetylene. Discounting the N₂O lost in the Control, the percentages of N₂O lost in relation to the total N applied were greater for urea (1.80%) than for MSW (0.50%), SM (0.46%), SPS (1.02%) or IPS (1.27%). In general, plots treated with organic fertilisers emitted higher amounts of N₂O when under maize than bare soil plots. On the other hand, greater denitrification losses were also recorded for plots in the absence of plants (between 9.7 and 29.3 kg N₂O-N ha⁻¹) than for areas with plants (between 7.1 and 24.1 kg N₂O-N ha⁻¹). The proportion of N₂O produced via denitrification was greater from fertiliser treatments than for the controls and also greater without plants (between 66 and 91 % of the N₂O emitted) than with plants (between 48 and 81%).