Effects of adding maize stover on the process of carrot waste composting

The disposal of vegetables waste can be a serious challenge in large-scale carrot planting. This study aims to clarify the effects of the different proportions of corn stalks on the maturity, gas emission, and enzyme activity in the composting of carrot wastes. A systematic analysis was also implemented to determine the response relationship among the maturity, gas emission and enzyme activity in the condition of a ventilation rate of 0.05 m³/min. The optimal proportion of excipients was then determined to realize the harmless and resource utilization of carrot wastes. The results showed that the composting products of different carrot wastes fully met the harmless standard of seed germination rate index (≥70 %). The emissions of NH₃ and CO₂ were also concentrated in the first seven days. The emission rate depended mainly on the physical and chemical properties, such as reaction temperature and pH values. Meanwhile, the addition of chicken manure resulted in the highest cumulative emission of NH₃. The single composting of carrot waste without any auxiliary materials (CK) obtained the highest CO₂ emission rate. There was a higher water content of carrot waste composting treatment (CK) and 7.5% straw addition treatment (T1) during composting, which was easy to produce leachate. The correlation and redundancy analysis was performed on the gas emission, maturity, and enzyme activity of all treatments. It was further confirmed that the emission of NH₃ and CO₂ was positively correlated with the temperature, but negatively correlated with pH. Furthermore, there was a significant positive correlation between catalase and maturity index. At the same time, the cellulase activity dominated the maturity of compost products. Therefore, the CO₂ emission from adding 15% straw auxiliary material (T2) was 14.83% lower than that of carrot vegetable waste composting alone (CK). The C/N ratio and porosity increased, whereas, the leachate output was reduced in the aerobic composting of carrot vegetables waste. Thus, the addition of 15% corn stalks (T2) reduced the leachate output and the emissions of NH₃ or CO₂ but increased the C/N and porosity. This finding can provide technical support for the resource utilization of carrot waste.