Minimum tillage mitigated soil N2O emissions and maximized crop yield in faba bean in a Mediterranean environment

Besides improving soil properties and N availability, N2-fixing crops may also mitigate soil N2O emissions, by reducing N fertilizer requirements. That said, the N released in their root exudates and through the decomposition of their residues may increase N2O emissions. Agricultural practices like tillage that affect soil parameters are known to influence the processes that lead to N2O production. However, the combined effect of the tillage system used and the crop type being cultivated on soil N2O emissions remains unclear, especially in a Mediterranean climate. A two-year study was carried out on a faba bean (Vicia faba L. var. minor Beck) crop as part of a long-term tillage experiment (> 20 years) in a Mediterranean environment. We evaluated the effects of two tillage systems, ploughing (P) and minimum tillage (MT), on the following parameters: N2O emissions, grain yield, N assimilated in plant biomass and biological N2 fixation. Our results showed grain yield to be higher in MT than P in the first year and roughly similar in the second. Moreover, cumulative N2O emissions were lower in MT than P in both years (up to −80%). Indeed, MT was identified in our environment as a sustainable means of achieving N2O emissions mitigation while also maximizing grain yield. Furthermore, the percentage of N derived from N2 fixation (Ndfa%) in plants stood at 80% on average, affected by tillage only in the second year, with higher values in P than MT. Moreover, a positive relationship between N2 fixation and N2O emissions was reported, particularly in P, and during the fallow period.