Rethinking organic fertilization in soilless systems: context, circularity and the need for a common framework

Abstract While taking big steps to increase the sustainability of soilless production systems through the integration of organic fertilization sources, the drivers and premises for their implementation do not seem to be entirely covered. There has been a scattered experimental approach to finding suitable organic sources and nutrient recovery technologies to overcome technical limitations, which seem relevant in the system’s footprint. Although recognized by some, the acceptance of soilless agriculture under the organic label is still under debate. This brief commentary addresses the concept of organic fertilizers in soilless agricultural systems, highlighting the importance of common premises to move forward. These include the local context of implementation, the choice of technology, scale and organic fertilizer source, as well as the employment of tools to integrate agronomic optimization with accurate analysis of environmental and economic sustainability performances. The importance of the organic waste source is discussed, considering it pertinent to align with the underlying principles of low-input farming, avoiding the generation of non-sustainable market chains or new waste for the sake of its circularity. Finally, it is proposed to strive for an alternative certification system for low-input and circular farming systems with common goals, also based on needs and available resource flow in urban and industrial settings. Significance of the study What is already known on this subject? The subject of organic fertilization in soilless agriculture is being greatly explored, while the strategic pathway and the requirements for the implementation can be unclear and underrepresented. What are the new findings? The present text does not present new data but intends to shed light on the challenges and inconsistencies of the current research direction, as well as encourage the definition of separate goals for certification in circular soilless systems. What are the expected impacts on horticulture? The present document aims to foster critical thinking on the choice of organic sources, emphasizing scalability and contextual awareness while avoiding reliance on unsustainable sources.