The Effect of Tillage on Faba Bean (<i>Vicia faba</i> L.) Nitrogen Fixation in Durum Wheat ((<i>Triticum turgidum</i> L. subsp. <i>Durum</i> (Desf))-Based Rotation under a Mediterranean Climate

Biological nitrogen fixation (BNF) is a sustainable approach to improving soil fertility that not only provides nitrogen to subsequent crops but also reduces the impacts of synthetic fertilizers. Here, a field experiment was established within the faba bean (<i>Vicia faba</i> L.), cv Prothabat 69-durum wheat (<i>Triticum turgidum</i> L. subsp. <i>Durum</i> (Desf)), cv Iride rotation framework of a long-term experiment in southern Italy to quantify BNF over two consecutive years (2012/13–2013/14). The effect of tillage systems (reduced, conventional, and no tillage) on faba bean N₂ fixation was estimated at the flowering and maturity stages via the natural abundance technique, using wheat as a reference crop. The effect of tillage on the percentage of nitrogen fixation from the atmosphere (Ndfa) and the amount of N₂ fixed (kg ha⁻¹) were higher under a no-tillage system in both years and at both growth stages, with values of 66.5% at flowering and 81.7% at maturity. The same trend was reported for the amount of N₂ fixed (kg N ha⁻¹) at both faba bean growth stages. The N balance was positive in both years, with a mean value of 40.4 kg N ha⁻¹, across all tillage systems; this value was greater in the no-tillage systems (45.7 kg N ha⁻¹) with respect to the others. The values for the organic matter content and stability index were higher under the no-tillage system, which provided favourable conditions that improved N₂ fixation by faba beans. The overall results indicate that no-tillage soil management represents a sustainable strategy for improving soil quality and fertility, therefore reducing the dependency of agriculture on synthetic fertilizers.