Tomato Production with Organic Fertilizer from Soluble Bonito Fish Waste in Hydroponic Cultivation Systems

Using organic fertilizer made from waste materials is beneficial for both the economy and the environment, promoting sustainability and reducing pollution. In hydroponics, decomposition converts these materials into fertilizer, with multiple parallel mineralization (MPM) enabling efficient nutrient conversion by microorganisms. The tomato cultivar “Momotaro Next” was cultivated hydroponically in order to determine whether organic fertilizer derived from soluble bonito fish waste (OF) through MPM could be used in tomato hydroponic cultivation compared with a chemical nutrient solution treatment (CF). In this study, ammonium (NH4+) was generated through the OF decomposition process. During cultivation, the ammonium concentration tended to increase, while the nitrate (NO3−) concentration tended to decrease. The total yield (TY), total dry matter (TDM), and leaf area index (LAI) were lower after OF treatment than after CF treatment. Notably, the TY, TDM, and LAI were 5.4 kg m−2, 594 g plant−1, and 1.7 for OF and 6.8 kg m−2, 895 g plant−1, and 3.8 for CF, respectively. The results of the tomato fruit qualities show no significant differences for total soluble solids (TSS) (%Brix), lycopene, glucose, fructose, or sucrose. However, significant differences were observed for gamma-aminobutyric acid (GABA), glutamate, aspartate, and citric acid. The lower yield and quality of the tomato crop with the OF treatment were caused by the high concentration of NH4+ that occurred during cultivation due to a nonoptimal mineralization process. Therefore, a well-managed MPM process could improve crop quality by reducing the risk of high NH4+.