Effect of chicken manure addition on humification of vegetable waste in composting process

In the process of vegetable production and processing, a lot of wastes are produced. Vegetable waste is a potential organic fertilizer source, rich in organic matter, nitrogen, and phosphorus nutrients, and composting is an important way to realize vegetable wastes utilization. However, the high lignocellulose content restricts the composting process, and the addition of chicken manure can accelerate lignocellulose degradation. However, the effect of the chicken manure on the humification of vegetable wastes in the composting process is still unclear. It is necessary to investigate the effects of chicken manure on lignocellulose degradation and humification during vegetable waste composting. The yellowed and dried melon vines were used as raw material (CK), and different proportions of chicken manure (25%, 50%) were added for aerobic composting. By analyzing the temperature, carbon and nitrogen changes, lignocellulose, humus, and seed germination index in the composting process, the effects of active substances added from chicken manure on lignocellulosic degradation and humification in the composting process of vegetable wastes were discussed. The results showed that the addition of chicken manure increased the content of active carbon and nitrogen (dissolved organic carbon and soluble nitrogen) of the initial materials, accelerated the temperature rise of the compost, and prolonged the high-temperature period of composting. The addition of 25% (CM25) and 50% (CM50) chicken manure promoted the degradation of lignocellulose and organic matter, with the highest degradation rates of lignocellulose reaching 61% and 69%, and those of total organic matter reaching 53% and 64%, respectively. The ideal addition of chicken manure (25%) effectively promoted the generation of humic acid, and the content of humic acid in CM25 treatment increased by 56.7% and 48.6% compared with CK and CM50 treatment, respectively. Interestingly, the CM50 treatment significantly promoted the degradation of organic matter and lignocellulose, and the degradation rates of organic matter and lignocellulose increased by 18.5% and 16.9%, respectively, compared with CK. However, the humic acid content was not significantly increased when the addition dosage of chicken manure increased to 50% since the lignocellulose tended to be completely degraded to CO₂. The results showed that treatment with 25% chicken manure had achieved the best performance on maturity parameters, the humification index, degree of polymerization, and germination index reached 14%, 3.5, and 83%, respectively. RDA analysis showed that the degradation of soluble organic carbon, lignocellulose, fulvic acid, and the formation of humic acid were the key factors to promote compost maturity. Therefore, the addition of chicken manure could significantly promote the degradation of lignocellulose in vegetable wastes. However, adding excessive amount of chicken manure lead to the complete degradation of lignocellulose and mineralization and CO₂ emissions, which is not conducive to humic acid formation. Appropriate addition of chicken manure is the key to accelerating the lignocellulosic degradation and promoting the formation of humic acid in the composting process of melon straw. The results can provide a theoretical basis for industrial production.