Effects of Digestate from Biogas on Agronomic Traits, Functional and Health Properties of Hydroponic Cultivation of Rocket (Diplotaxis tenuifolia L.) and Parsley (Petroselinum crispum Mill.)

The study aimed to use vermicompost (V) from solid digestate and liquid digestate (LD) from biogas as renewable and sustainable growing medium and nutrient solution in a hydroponic cultivation of wild rocket (Diplotaxis tenuifolia L.) and parsley (Petroselinum crispum Mill.), under greenhouse condition. Four different combinations were considered, where peat (P) and standard solution (SS) were used as a comparison: P + SS, P + LD, V + SS, V + LD. Phytotoxicity was never induced on rocket, while a strong biostimulant effect was induced by vermicompost in parsley. In rocket V + SS showed the highest values of root dry weight (0.38 ± 0.05 g), while V + LD ensured optimal leaf size (around 10 cm). V + SS positively affected all growth parameters in parsley. Vermicompost induced positive effect on physiological parameters in both species (high values of specific leaf area and reduced transpiration rate). P + LD induced the highest values of polyphenolic compounds in both cuts for parsley and in the first cut for rocket. V + LD positively affected total phenols content, flavonoid productions and antioxidant powers in parsley. Qualitative analysis showed six different glucosinolates and several kaempferol derivatives in rocket, while parsley exhibited a higher number of polyphenolic compounds. PCA models indicated that the different substrate impacted the metabolites expression, V and LD inducing richness in sinapic acid derivatives in rocket, and higher concentration of apigenin derivatives in parsley. Our results suggest that V and LD could be valid alternatives to P and SS and that they could improve the leaf quality when combined together.