Bio-based fertilisers (BBFs) are gaining attention as sustainable alternatives to mineral fertilisers due to their potential for nutrient recovery, reduced environmental emissions, and improved soil health. However, their broader adoption is hindered by regulatory uncertainty, quality inconsistencies, and methodological variability in assessing their environmental impacts. This study can reveal about the body of research on bio-based fertilisers (BBFs), using a hybrid methodology that combines bibliometric and content analysis. A total of 247 publications from 2001 to 2024 were reviewed to identify research trends, environmental concerns, and assessment approaches. Results show a sharp increase in BBF-related publications after 2016, driven primarily by European and North American research, with growing focus on life cycle assessment (LCA) and nutrient recovery. The in-depth analysis of the ten most cited LCA and non-LCA studies highlights key methodological differences: non-LCA studies frequently rely on empirical fieldwork and generate primary data, whereas LCA studies typically synthesise secondary data to provide broader system-level insights. Despite this complementarity, the lack of methodological harmonisation poses a barrier to consistent comparison and interpretation. The findings highlight the need for a unified, standardised assessment framework to reliably evaluate the environmental performance of BBFs and support their effective implementation within circular and sustainable agricultural systems.

Recovering phosphorus (P) through combustion from waste streams, like wastewater sludge and animal manure, offers a promising solution. This research explores the P release patterns in different ashes derived from secondary raw materials, using a long-term soil incubation lasting 160 days. The study evaluated the P release dynamics in five types of ashes from enhanced biological phosphorus removal (EBPR) systems and pig slurry burned at different temperatures. According to the results, a primary effect was observed on P bioavailability during the initial incubation period. All tested ashes release more than 50% of the total P applied between days 5 and 10. Ashes from EBPR exhibited higher P release than those from pig manure, indicating ash origin as a key factor in P release. Additionally, combustion temperature was crucial, with higher temperatures resulting in increased P release rates. Furthermore, the Pearson correlation revealed a strong relationship between the characteristics of the ashes and the amount of P release. Overall, these findings suggest that ashes could be a valuable P-source for agriculture avoiding the process of wet chemical P extraction, thus reducing both economic and environmental costs.