Evaluating the impact of rice husk on successions of bacterial and fungal communities during cow manure composting

Abstract

Although rice husk (RH) has been used as a compost additive, the microbes present in RH are not well understood. In this study, we explored the physicochemical parameters, the microbial population and functional succession to better understand how different levels (T0: 0; T1: 20%; T2: 30%) of RH affected the performance of cow manure composting. Higher thermophilic temperatures (70 °C) and higher-quality compost with respect to pH, the C/N ratio, particle-size distribution and other characteristics were obtained with the addition of 20% RH. The total nitrogen and germination index (GI) of the final product (T1) increased by 48% and 175%, respectively, compared to those of T0. Moreover, fluorescence spectra indicated that the degradation of protein-type groups and the formation of humic substances increased in T1. Microbial analyses indicated that interactions between bacterial communities were also strengthened in T1. We also found that Sphaerobacter and Myceliophthora were the unique and dominant thermophilic genera of bacteria and fungi, respectively, in RH-supplemented compost. Carbohydrate metabolism and amino acid metabolism were the main metabolic pathways, and saprotrophs represented the dominant fungal trophic mode in the composting process. In T1, bacteria were mainly affected by temperature and pH, while fungi were more affected by moisture. This study found a suitable RH dosage for composting and provides a microbiological basis for RH as a compost additive.