Abstract
Sustainable agriculture relies on replacing fossil-based mineral fertilizers, which are highly cost-energetic to produce, and demand extensive use of scarce natural resources. Today, agronomic practices within the concept of circular economy are emerging and, as such, the exploitation of digestate as a biofertilizer and soil amender is extensively investigated. This study aimed at evaluating the agronomic potential of liquid digestate as the sole nutrient source for hydroponic cultivation of baby lettuce in greenhouses. Growth rate, physiological responses, concentration of secondary metabolites, and nutrient uptake were compared between baby leaf lettuce grown in digestate in concentrations of 5, 10, and 20% diluted in water (either with or without pH adjustment) and in Hoagland solution (control). Results showed that the production yield was negatively correlated with the concentration of the added digestate. Nevertheless, the antioxidant capacity was significantly enhanced in 5 and 10% liquid digestate treatments compared to the control. Additionally, the nutrient composition in the baby leaf lettuce and the reduction in nutrient concentrations in the growth media demonstrated efficient mineral uptake by the plants. Thus, the application of liquid digestate as a fertilizer in hydroponic systems is a promising practice to recover residual resources, leading to the transition towards more sustainable greenhouse production.
Highlights
Anaerobic digestion is a widely applied process for the valorization of organic residues, with simultaneous production of green energy [1,2]
The present study demonstrates an efficient application of liquid digestate as a fertilizer for the hydroponic cultivation of baby lettuce grown in a greenhouse using a floating system
Even though the plant growth was affected by the increased digestate concentration, the qualitative characteristics of the baby leaf lettuce demon
Summary
Anaerobic digestion is a widely applied process for the valorization of organic residues, with simultaneous production of green energy (i.e., biogas) [1,2]. After the anaerobic decomposition of influent feedstocks, large quantities of digestate (i.e., welldigested effluent) are generated. The physicochemical characteristics of digestate may vary significantly from one biogas plant to another, due to the different nature and composition of the influent feedstock, and due to specific operational parameters of the overall process (e.g., operational temperature of the reactor). Biogas plants that treat agricultural/livestock byproducts (e.g., manure or silages) generate digestate that contains a high solid fraction due to the fibrous recalcitrant material. A more liquid digestate is the outcome of biogas reactors processing agro-industrial wastewater
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