Cactus pear (Opuntia ficus-indica) in areas with limited rainfall for the production of biogas and biofertilizer. (20th March 2021) - Quiroz, Madelaine; Varnero, María Teresa; Cuevas, Jaime G.; Sierra, Hugo
Abstract: An insecure energy supply has promoted the search of alternative energies. Anaerobic digestion can produce methane from energy crops. Opuntia ficus-indica or cactus pear can produce high amounts of dry matter (DM), 10 Mg ha −1 y −1 with an average rainfall of 400 mm y −1 . It is a crop with a high efficiency in the use of water (4.6 mg DM g −1 H2 O) and can grow on land not currently used for the production of other crops. This review found that Opuntia productivity strongly depends on agronomic management (50 Mg ha −1 y −1 ). The increase in DM is reflected in an increase in the theoretical yield of biogas and methane. Opuntia cladodes have a high potential for producing methane (327 m 3 CH4 Mg −1 VS) because their carbohydrates have a low fiber content and are easily degraded. To optimize the production and quality of the biogas produced from Opuntia, its cladodes would have to be mixed with other raw materials (e.g. manure, plant residues, microalgae) and C/N ratio (16–30) for microorganisms in the digestate; the pH would also have to be modified to a neutral-alkaline range (the cladodes have a pH between 3.5 and 5.5) for the same reason. The resulting digestate could be applied to the soil as a biofertilizer, improving its properties as well as crop productivity. This is important, above all, in soils in semi-arid zones. Finally, there are several challenges to validate Opuntia as an energy crop, especially from a holistic viewpoint that considers economic, social and environmental aspects. Highlights: Cactus pears could produce biogas and biofertilizer in areas with limited rainfall. Intensification of management would increase cladode biomass and methane potential. Factors as logistics, crop and biogas production scaling and subsidies must be evaluated. Factors that determine Opuntia's profitability must be comprehensively addressed.