The Effect of Tillage on Faba Bean (Vicia faba L.) Nitrogen Fixation in Durum Wheat ((Triticum turgidum L. subsp. Durum (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 (Vicia faba L.), cv Prothabat 69-durum wheat (Triticum turgidum L. subsp. Durum (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.