Soil N2O emissions in Mediterranean arable crops as affected by reduced tillage and N rate

Nitrous oxide (N2O) is emitted from agricultural soils as a product of biotic pathways of the nitrogen (N) cycle. Agricultural practices may affect soil water content, temperature and N availability, and consequently N2O emissions. Thus, it is necessary to identify strategies to mitigate N2O emissions while maintaining crop yields. This two-year study on durum wheat and sunflower in a Mediterranean environment evaluated the influence of tillage intensity (plowing vs. minimum tillage) and N fertilizer rate (N0, N1 and N2: 0, 110 and 170 kg N ha(-1), respectively, for wheat, and 0, 80 and 140 kg N ha(-1), respectively, for sunflower) on crop yields and N2O emissions. Reducing the N fertilizer rate by ca. 40% resulted in an average mitigation of ca. 35% of cumulative N2O emissions during the growing season of both crops. From N1 to N2, the grain yield of sunflower did not increase, but that of wheat did so by ca. 25%. Indeed, yield-scaled N2O emissions of N0, were the highest in wheat (259 +/- 45 g N2O-N Mg-1 dry grain, 12.2 +/- 2.0 g N2O-N kg(-1) N uptake) and the lowest in sunflower (62 +/- 7 g N2O-N Mg-1 dry grain, 2.0 +/- 0.2 g N2O-N kg(-1) N uptake). Reducing tillage intensity decreased cumulative N2O emissions significantly only for sunflower during the second year (by 35%), but not for any other treatment. The effect of the reduced tillage depth on grain yield varied between the 2 years, being negative only under wetter growing seasons (- 12% in wheat and - 9% in sunflower).