Enhancing Sustainable Waste Management Using Biochar: Mitigating the Inhibitory of Food Waste Compost from Methane Fermentation Residue on Komatsuna ( Brassica rapa ) Yield

Methane fermentation, utilizing food waste (FW), is viewed as a sustainable strategy that leverages garbage and agricultural waste to conserve the environment. However, FW compost encounters growth inhibition issues, which we examine in this study. The aim of this study was to assess the influence of various compost mixtures on seed germination growth and the yield of Komatsuna ( Brassica rapa ). The experiment employed FW compost mixtures with biochar (BC), clay (CL), weeds (WD), and a control group in a completely randomized design with three replications to monitor germination. The experimental pots, arranged in a complete factorial design, involved three treatment factors: compost type (FW or HM), biochar presence or absence (WB or NB), and three input rates (25 g pot −1 , 50 g pot −1 , and 100 g pot −1 ), each in triplicate. The combination of FW and BC exhibited an enhanced germination rate compared to FW alone. Moreover, the inclusion of biochar significantly amplified this effect, particularly at the input rate of 50 g pot −1 and had a substantial impact on the interaction between input rate, compost type, and biochar on variables such as nitrogen (N) uptake, % N, soil carbon, and yield. Homemade BC demonstrates an increasing fertilizer cost performance (FCP) as the input rate rises across all fertilizer combinations, while commercially priced BC exhibits a reverse relationship with FCP. These findings suggest that the addition of biochar enhances the performance of methane fermentation residue compost, thereby promoting plant growth through the processing of environmentally sustainable waste.