DESIGNING NOVEL PEAT-FREE ORGANO-MINERAL FERTILIZER FROM BIOWASTES

Organo-mineral fertilizers (OMFs) are a mixture of an organic fraction with one or more mineral fertilizers. Due to its well-known physical and chemical properties, peat is used widely as the organic fraction in OMFs with low organic carbon and high mineral nutrient concentrations. However, there is a need to identify viable alternatives to peat in OMFs, aiming to reduce reliance on geogenic materials and foster a circular approach to utilizing industrial and municipal organic waste. By examining various bio-waste materials subjected to different stabilization processes, this study aims to provide insights into their potential as substitutes for peat in OMF formulations containing 7.5% organic carbon (Corg) and their impact on nutrient availability, nutrient losses, and plant uptake efficiency. This thesis proposes to analyze over four chapters the viability of a peat replacement in five steps: i) identify biowastes with chemical and physical parameters that allow a direct replacement of peat in OMFs with a formulation containing 7.5 Corg regardless of their similarity to peat; ii) verification of an immobilization process of the mineral fertilizers promoted by an organic material; iii) analyze the OMF nutrient availability and crop uptake in the short term after fertilizing with biowaste and peat granular OMFs; iv) analyze tomato growth evolution over time and final nutrient uptake as an indicator of nutrient availability of biowaste and peat granular OMFs during 75 days. During the PhD, multiple biowaste materials collected across Italy were physically and chemically characterized and compared to peat. Biowaste materials were analyzed to determine if they could be used as part of an OMF with 7.5% Corg. Mixtures of solid organic fractions, mineral fertilizers in solution, and granular OMFs were made with the most promising biowastes and analyzed in different studies for crop nutrient uptake at different periods and plant species. Complementary studies about the nutrient concentration in soil, soil respiration, and plant nutritional status over time were performed to understand the nutrient dynamics of OMFs. The results show that no biowaste was similar to peat in all its characteristics, and all materials require one or more physical processes before being used as a replacement. After processing, biowaste materials can be used to formulate OMFs with 7.5% Corg and a high concentration of mineral fertilizers. However, biowaste OMFs underperform peat OMFs and mineral controls after one and two months for yield and nutrient uptake. Lower nutrient use efficiency and yield differences in biowaste OMFs are explained by a lower concentration of plant-available phosphorus (P) in soil compared to peat OMF and mineral controls. Nevertheless, biowaste OMFs had a similar nutrient use efficiency and tomato yield compared to a peat OMF and mineral controls after 75 days, indicating that biowaste materials are promissory replacements of peat in OMF used in crops with long growing periods. Biowaste materials increased nitrogen (N) volatilization in the soil, although not to the extent that affected the yield after 75 days; however, without modifying the pH of biowaste, they are not recommended for OMFs containing high concentrations of N. By promoting a circular approach to waste management and fertilizer production, biowaste OMFs offer a promising pathway toward sustainable agriculture and environmental stewardship. However, biowaste may require additional physical steps to increase the quality of its manufacturing. It is necessary to analyze the benefits of manipulating the biowaste over extracting and transporting peat before widely recommending the biowaste OMFs obtained in this project.