Suitability of renewable organic materials for the synthesis of organo-mineral fertilizers: Driving factors and replacement of peat

In organo-mineral fertilizers (OMFs) with low organic carbon (C_org) final content, the organic fraction enhances the mineral fraction efficiency. Therefore, a high-quality organic fraction is crucial. While geogenic materials like peat have been used extensively for producing high-quality OMFs, exploring alternative organic sources such as biowastes can add circular value to these fertilizers. However, since biowastes vary significantly based on origin, processing, season, or collection area, each material must be analyzed separately for suitability in OMFs. We propose a set of physicochemical parameters impacting OMF formulation, manufacture, and potential use to facilitate this analysis. Our study involved the collection of 16 organic materials across Italy, categorizing them into geogenic materials (peat and leonardite), wood biochar (BC), green compost (GC), farmyard manure compost (MC), municipal solid waste compost (MSWC), and vermicompost (VC). After characterization, we analyzed the contribution of each organic material to an OMF with 7.5 % C_org, in which a low amount of nutrients derives from the organic material. Most parameters showed high variability among groups; no material matched peat and leonardite across all parameters. However, the C_org stability in composted biowastes was generally acceptable for OMF use. Granulometry (>5 mm), pH (>8), and formula space (>90 %) obligate blending with another organic fraction, while P and K in the raw material are insignificant for low C_org OMFs. Most examined materials had potential for OMF production, though adjustments are necessary to enhance their quality. Based on the proposed parameters, MSWC and VC samples stood out as potential high-quality organic matrices for OMF production, offering a promising alternative to peat. The prospect of replacing peat in OMF manufacturing with biowastes holds promise, mainly when industries can search for local substitutes.