Tillage and nitrogen fertilization effects on nitrous oxide yield-scaled emissions in a rainfed Mediterranean area

There is a strong need to identify the combination of tillage and N fertilization practices that reduce the amount of nitrous oxide (N2O) emissions while maintaining crop productivity in dryland Mediterranean areas. We measured the fluxes of N2O in two field experiments with 3 and 15 years since their establishment. In the long-term experiment, two types of tillage (NT, no-tillage, and CT, conventional intensive tillage) and three mineral N fertilization rates (0, 60 and 120 kg N ha−1) were compared. In the short-term experiment, the same tillage systems (CT and NT) and three N fertilization doses (0, 75 and 150 kg N ha−1) and two types of fertilizers (mineral N and organic N with pig slurry) were compared. N2O emissions, water-filled pore space, soil mineral N content, grain yields, N-biomass inputs and soil total nitrogen (STN) stocks were quantified and the N2O yield-scaled ratio as kg of CO2 equivalents per kg of grain produced was calculated. In both experiments tillage treatments significantly affected the dynamics of N2O fluxes. Cumulative losses of N as N2O were similar between tillage treatments in the long-term field experiment. Contrarily, although not significant, cumulative N losses were about 35% greater under NT than CT in the short-term experiment. NT significantly increased the production of grain and the inputs of N to the soil as above-ground biomass in both experiments. Averaged across fertilizer treatments, CT emitted 0.362 and 0.104 kg CO2 equiv. kg grain−1 in the long-term and the short-term experiment, respectively, significantly more than NT that emitted 0.033 and 0.056 kg CO2 equiv. kg grain−1, respectively. Nitrogen fertilization rates did not affect the average N2O fluxes or the total N losses during the period of gas measurement in the long-term experiment. Contrarily, in the short-term experiment, N2O emissions increased with application rate for both mineral and organic fertilizers. The use of pig slurry increased grain production when compared with the mineral N treatment, thus reducing the yield-scaled emissions of N2O by 44%. Our results showed that in rainfed Mediterranean agroecosystems, the use of NT and pig slurry are effective means of yield-scaled N2O emissions reduction