Effects of Biochar and Zeolite on the Co-Composting of Agricultural Waste Under Psychrophilic Conditions

Biochar and zeolite are promising additives for improving composting; however, their effects during the co-composting of agricultural waste have not yet been sufficiently studied. This study evaluated their influence on the composting of green onion residues and chicken manure under psychrophilic conditions on a pilot scale using 200 kg piles. Three treatments were evaluated: a control, 5% biochar, and 2% zeolite. Both amendments increased the maximum composting temperature by approximately 3 °C and improved the germination index, with increases of around 10% for biochar and 26% for zeolite compared to the control. Biochar increased the relative abundance of the amoA gene, associated with ammonia oxidation and nitrification, suggesting greater biochemical potential for nitrification. During maturation, zeolite reduced pH and electrical conductivity, indicating greater compost stability. In fast-growing crops, compost from zeolite treatment did not significantly affect plant growth when applied alone, but improvements were observed when combined with synthetic fertilizer. Overall, both additives improved composting performance and compost quality, with zeolite showing the most consistent effects.