Effect of Phanerochaete chrysosporium inoculation in different times of rice husk and chicken manure composting on humification of compost

In the process of rice processing, a large amount of agricultural organic solid waste (e.g., rice husk) is produced, and composting is an effective way to realize resource utilization of rice husk. However, lignin in rice husk has a complex structure and is not easy to be degraded, and the high content of lignin limits the composting of rice husk, and exogenous inoculation of Phanerochaete chrysosporium can accelerate the degradation of lignocellulose. However, the effect of inoculation of P. chrysosporium in different composting times on the humification process of rice husk composting is not clear. Therefore, in this study, rice husk and chicken manure were used as raw materials, P. chrysosporium was inoculated in the 18^th day of composting (cooling stage of composting, T2), and 0 day of composting (T3, beginning of composting), for aerobic composting, with T1 (no inoculation) as the control. By analyzing composting temperature, pH, C/N, seed germination rate, lignin peroxidase, manganese peroxidase, lignin content, cellulose content and humus to explore the effect of inoculating P. chrysosporium at different composting times on the degradation of lignin and cellulose, the changes of key enzyme activities and their coupling with the process of humification, the promoting effect of inoculating P. chrysosporium on composting humification was determined. The results showed that the lignin peroxidase (LiP) and manganese perosidase (MnP) activities, lignin and cellulose degradation rates and humification degree were significantly increased after P. chrysosporium inoculation during the cooling period (T2). At the end of composting, the cellulose content of T2 treatment decreased from 0.30 g∙g⁻¹ of initial compost to 0.09 g∙g⁻¹, and the lignin content decreased from 0.24 g∙g⁻¹ of initial compost to 0.03 g∙g⁻¹. Compared with T1, the contents of lignin and cellulose decreased by 78.57% and 52.63% (P<0.05) under T2 treatment, and 57.14% and 40.00% (P<0.05) under T3 treatment. T2 treatment increased the humus content by 67.84% and 52.33% (P<0.05), respectively, compared with T1 and T3. Various maturity indexes showed that the compost quality of T2 treatment was significantly improved, the humification rate (HR), ratio of humic acid to fulvic acid (HA/FA) and percentage of humic acid (PHA) reached 51.64%, 2.72 and 73.39%, respectively, significantly higher than T1 and T3 (P<0.05). The results of correlation analysis showed that the contents of lignin and cellulose were significantly negatively correlated with the activities of lignocellulosic degradation enzymes (LiP and MnP) (P<0.05, P<0.01); Redundancy analysis (RDA) showed that degradation rate (explanatory degree=88.2%, P=0.002), cellulose content (explanatory degree=74.3%, P=0.002) and lignin content (explanatory degree=72.5%, P=0.002) had the most significant effects on the maturity index. These results indicated that the degradation of lignin and cellulose promoted the formation of HS, the deep degradation of lignin and cellulose promoted the complexity of HS structure and made the HS structure more stable. Therefore, inoculation of P. chrysosporium in the cooling period of composting promoted the deep degradation of lignin and cellulose by improving the activities of LiP and MnP, thus strengthened the humification process of composting and improved the quality of compost, and provided theoretical basis for the composting production of rice husk.