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Research was carried out in southern Italy with the aim to assess the quality of faba bean residual biomass and its potential for biorefinery application. Faba bean is a sustainable crop, due to its ability to fix atmospheric nitrogen, and a large amount of biomass remains after harvest which can be valorised for energy production. Greenhouse and early planting are known to affect pod yield and, in this respect, even the residual biomass quality needs to be assessed. For this purpose, the effects of five planting times (i.e. the dates of transplants ranging from 27 September to 22 November at two-week interval, earlier and later than the common planting date of 25 October in Naples province) on pods yield, residual biomass, and saccharification potential were evaluated in faba bean grown in open field and in greenhouse. The third planting time resulted in the highest fruit and residual biomass yield under greenhouse, whereas the fourth was the best in open field. Harvest index was best affected by the third and fourth planting times in open field. Greenhouse grown biomass showed higher values of lignin, hemicellulose and pectin, compared to open field, whereas the opposite trend was recorded with cellulose. Lignin content showed a gradual decrease from the first to the last planting time (17.7%-13.7% biomass fraction respectively), as well as pectin (from 14.1 to 11.5% biomass fraction); conversely, cellulose increased from the first to the last planting time (from 41.1 to 48.7% biomass fraction). Glucose was the most represented monosaccharide (46.7 mol%), followed by xylose (27.4 mol%) and galactose (9.9 mol%). Overall, the potential of faba bean residual biomass for energy production was best affected by open field growing, the latest planting time and alkali pre-treatment, the latter giving the highest value of saccharification (60.7 g kg −1 h −1 compared to 27.6 relevant to hot water pre-treatment).

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Background: Broad bean fits sustainable agriculture model due to symbiosis with Rhizobium, the seeds being a good source of energy, proteins, polyphenols, and fiber. The large amount of broad bean biomass residues can be employed for biofuel production, thus valorizing the overall production process. This research was aimed to investigate on the effects of farming management, such as greenhouse cultivation and appropriate planting time on the qualities of broad bean seeds and residual biomass for conversion into biofuel. The related balances of energy gain associated to both ethanol yield and nitrogen fertilizer saving due to Rhizobium nitrogen fixation were assessed. Methods:Research was carried out on broad bean in Portici, province of Naples, southern Italy, based on the factorial combination of two farming systems (open field, greenhouse) and five planting times: 27 September and 11 October, to obtain early production; 25 October, which fell in the usual period for broad bean planting in the province area; and 8 November and 22 November, for late production. For each of these cultivation conditions, the quality of seeds, in terms of protein, fiber and antioxidant concentrations, and of crop residual biomass were determined. In addition, the energy yield as ethanol production from residual biomass and nitrogen fertilizer saving due to Rhizobium atmospheric fixation were assessed. Results and discussion:The highest plant nitrogen uptake was recorded under the fourth planting time in open field and the third in greenhouse, the average accumulation attaining 87% in residual biomass, 7.4% in pods, and 5.6% in seeds. Seed protein content was 12.6% higher in greenhouse than in open field and 16.2% higher under the latest planting time compared to the earliest one. Seed polyphenol concentration was higher in open field than in greenhouse and with the two earliest planting times. Greenhouse grown biomass showed higher values of lignin, hemicellulose and pectin, compared to open field, whereas the opposite trend was for cellulose. Lignin showed a decrease from the first to the last crop cycle, opposite to cellulose, and glucose was the most represented monosaccharide. Both the highest theoretical ethanol and overall energy production were highest with the fourth planting time. Conclusions:Greenhouse management enabled broad bean plants to accumulate higher proteins in seeds, but open field conditions resulted in better residual biomass quality for ethanol and Rhizobium-depending energy production.