Sustainable Valorization of Grape Pomace Digestate as Fertilizer: Effects on the Agronomic and Biochemical...

This study explores the sustainable valorization of grape pomace digestate as a biofertilizer for the cultivation of Calendula officinalis L., a medicinal and edible flower with significant functional potential. Grape pomace, a major byproduct of winemaking, was subjected to anaerobic digestion to produce a nutrient-rich digestate applied at 0, 10, 20, and 30% concentrations under four irrigation regimes (57-232 mL day^-1). Two seasonal greenhouse experiments evaluated agronomic performance, flower yield, and biochemical composition. Moderate to high digestate applications (20-30%) markedly enhanced flower yield and aerial biomass, while promoting the accumulation of proteins, lipids, soluble sugars, carotenoids, and phenolic compounds. Flowers grown under these conditions exhibited elevated β-carotene levels (80.97 mg 100 g^-1) and strong antioxidant activity (>1300 μmol TEAC 100 g^-1), supporting their potential in functional foods, nutraceuticals, and natural colorants. Seasonal variation influenced metabolic responses, with summer enhancing sugar and carotenoid synthesis and winter favoring pigment stability. The digestate was free from toxic elements and improved substrate fertility, confirming its agronomic safety and efficiency. A sustainability evaluation yielded an EcoScale score of 89.8, substantially higher than values reported in comparable literature, underscoring the high environmental performance and process greenness of this approach. Overall, this work presents a scalable, eco-efficient strategy to convert winery residues into high-value floral biomass, advancing circular bioeconomy principles and sustainable agricultural practices.