Production of Plant Biostimulants from Microalgae Grown on Biogas Digestate and Tests on Selected Crops

This study investigates the potential of microalgae-based biostimulants cultivated on the liquid part of anaerobic digestate as a sustainable solution for modern agricultural chal-lenges. The liquid part of anaerobic digestate, a nutrient-rich by-product of biogas pro-duction, is used as a growth medium for the microalgae Scenedesmus sp. to illustrate the principles of circular bioeconomy by converting organic waste into valuable agricultural products. The microalgae Scenedesmus sp. were cultivated in open raceway ponds, har-vested using sedimentation, microfiltration or centrifugation, and further dried in venti-lated cabinet at 35°C. Laboratory germination tests and field trials were conducted to eval-uate the efficacy of the produced algae as plant biostimulant. In laboratory tests microal-gae-derived biostimulants significantly improved seed germination and root develop-ment of garden cress at all concentrations, Proso millet gave positive response to 1 and 5 g DM/L, however cabbage showed no response. Foliar applications on Proso millet in the field trial further highlighted its potential to improve crop yields stability across the field after but not increased millet grain yield. This research highlights the viability of integrat-ing microalgae cultivation with waste management systems to produce biostimulants that can improve crop production while supporting sustainable agriculture.