Evaluation of biogas digestate as a sustainable nutrient source for soilless lettuce cultivation: characterization and effects on growth and physiological responses

The growing demand for sustainable food production highlights the need to recycle organic waste streams within agricultural systems. This study explores the valorization of biogas digestate derived from cattle manure as a nutrient source in soilless cultivation systems, including Flow-Type Hydroponic Cultivation (FHC), Pyramid Aeroponic Cultivation (PAC), and Solid-Medium Cultivation (SMC). Biogas was produced through mesophilic anaerobic digestion, and the digestate was sanitized at 70 °C to ensure its safety for agricultural application. Digestate treated in a closed system exhibited a higher ammonium concentration, providing a more plant-available nitrogen form compared to that treated in an open system. While the digestate alone was insufficient to achieve maximum yields, its supplementation with the Hoagland nutrient solution substantially promoted plant growth Notably, the PAC system increased planting density by approximately 34% per unit area relative to the FHC and SMC systems, resulting in superior root development, higher photosynthetic efficiency (SPAD), and improved productivity. These results demonstrate that biogas digestate can function as a circular, resource-efficient fertilizer, contributing to sustainable nutrient cycling and reduced environmental impacts in modern agricultural practices.

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