Sulla (Hedysarum coronarium L.) as Potential Feedstock for Biofuel and Protein

Although sulla (Hedysarum coronarium L.) has many interesting features that could support the production of biofuels (e.g., a high yield and soluble sugar content, N-fixation capacity, low input requirements for its cultivation), no study has assessed the possibility of its use for that purpose. Our objective was to evaluate the potential value for energy production of sulla cut at various stages of growth. Furthermore, the potential of sulla as a dual purpose crop (energy and feed) was investigated. The crop was grown in rainfed conditions in a typical Mediterranean environment (over two complete 2-year crop cycles) and was cut at four different phenological stages. The biomass was divided into two fractions (stems and leaves), weighed, and analyzed to estimate the theoretical production of bioethanol and biomethane and the feed value of the whole biomass and of the two fractions. The total dry matter yield in the 2-year crop cycle was about 18 Mg ha−1; this level of production is similar to or higher than that of most other crops grown in the same environment in rainfed conditions. The stems had a high content of total soluble sugars (even higher than 200 g kg−1) and cell wall polysaccharides, markedly higher than the leaves. The leaves contained most of the protein of the plant, representing an actual protein concentrate. Thus, the crop seems particularly suitable for dual purpose use if stems are allocated to the production of biofuels and leaves to the production of livestock feed. Moreover, the results showed that the early seed set stage is the most appropriate cutting time for maximizing yield both for energy and for livestock use.