Impact of carbon composite on the germination of Trifolium pratense (red clover) in two different soil types

Agro-waste materials can be transformed into valuable soil conditioners that improve soil quality and crop establishment. This study evaluated eco-friendly composites prepared from eggshell and bagasse, pyrolyzed at 450 °C and 600 °C in fourteen blend ratios, with a heating rate of 20 °C/min. Composites were then evaluated on two different soils to enhance plant growth, and improved soil quality. A standardized germination assay was conducted with Trifolium pratense (red clover), using 20 g of soil per petridish and eight seeds per replicate in a complete randomized block system. The fourteen carbon composite green conditioners were added on each at the rates of 0 and 5%. Soil physicochemical properties and plant responses were analyzed using SPSS to juxtapose the effect of composite on seedling and control group. The result revealed that the ash content in eggshell: bagasse 4:1 at 600 °C was optimum at (84 ± 0.20), while 100% eggshell had high levels of ash at both temperatures (20–23%). Germination and shoot development were significantly enhanced by several treatments (p < 0.05), whereas root growth showed weaker responses. Multivariate analysis confirmed that soil and composite interactions strongly influenced seedling traits (p < 0.001). These findings demonstrate that eggshell–bagasse composites provide synergistic benefits by combining Ca-rich and C-rich waste properties, thereby enhancing early plant growth and improving soil quality. The study highlights a low-cost, sustainable strategy for recycling agricultural residues into effective soil amendments.