Faba beans should be inoculated with Rhizobium leguminosarum (biovar viceae) bacteria to promote biological nitrogen fixation. This inoculant species is the same for peas and lentils but check with the manufacturer about different strains of R. leguminosarum. This article provides more information about research on rhizobia for faba bean inoculants.
Faba beans can fix approximately 90% of their N-requirement. This high N2-fixing capability means that faba beans can leave behind an N-credit for subsequent crops, making them a nice addition to crop rotations. Although starter N fertilizer is not necessary, ensure soil test N levels are low enough to accommodate nodulation. The first root nodules will form approximately two to three weeks after emergence and peak N2-fixation will occur just after flowering.
Faba beans are efficient at extracting phosphorus. For long-term management, ensure nutrient inputs balance with grain removal throughout a rotation. See Table 1 for average nutrient removal rates of faba beans. According to research conducted at the University of Saskatchewan, up to 40 lbs P2O5/ac can be seed-placed safely with faba beans. Research on faba bean nutrient uptake and nitrogen fixation is ongoing at the U of S in Dr. Jeff Schoenau’s lab, so stay tuned for more results.