Mixed-species aquatic weed fertilizers enhance Brassica rapa growth through nutrient synergy within circular nutrient recovery systems

Background: Submerged aquatic weeds pose persistent management challenges in freshwater ecosystems, yet their rapid biomass accumulation and nutrient-rich composition represent an underutilized resource for sustainable agriculture. Valorizing this biomass may help link freshwater ecosystem management with circular nutrient recovery and climate-resilient food systems. This study evaluated the agronomic potential of three dominant submerged macrophytes Egeria densa , Elodea nuttallii , and Vallisneria sp as organic fertilizers for Brassica rapa L. var. perviridis , with particular emphasis on comparing single-species and mixed-species formulations integrated with locally available organic residues. Results: A greenhouse experiment was conducted using a completely randomized design with 26 treatments, including four aquatic-weed–based fertilizers (three single-species and one mixed-species), applied at three dosage levels and in two application forms (raw solid and liquid extract), alongside unfertilized and standard commercial controls. Fertilizer identity emerged as the primary determinant of plant performance, consistently outweighing the effects of application dose and form. Across biomass production and morphological traits, the mixed-species fertilizer produced the highest and most stable responses, particularly in shoot fresh and dry biomass, plant height, and leaf production. Single-species fertilizers showed intermediate and species-dependent performance, while Vallisneria -based formulations consistently resulted in lower growth. Dose effects were secondary and fertilizer-dependent, and application form had minimal influence. Growth enhancement was primarily driven by increased aboveground biomass and canopy development, while root biomass, shoot–root allocation, and leaf chlorophyll index remained largely unchanged. Conclusions: These results demonstrate that combining multiple submerged aquatic weed species into a single fertilizer formulation confers clear agronomic advantages over single-species applications. Mixed-species aquatic weed fertilizers enhance nutrient-use efficiency and crop growth without increasing application complexity, supporting their potential role in circular nutrient recovery strategies, sustainable vegetable production, and climate-resilient agricultural systems under increasing environmental variability.