Using a vermireactor with a cow dung and shell powder mixture to improve the properties of vermicompost: a field study

Cow dung and oyster shells are not fully utilized in China and result in severe pollution and damage to the environment. A field study was conducted to determine the effect of additives produced from oyster shells, oyster shell powder (OSP), and modified oyster shell powder (MOSP), on the properties of a vermicompost obtained from a vermireactor with a cow dung and shell powder mixture. The results showed that both MOSP and OSP, particularly MOSP, increased pH, total nitrogen (TN) content, and surface area while decreasing EC and organic matter content in the derived vermicompost, the final vermicompost had a much higher degree of maturity based on the increased germination index (GI) and decreased NH₄⁺/NO₃⁻(NI), and their properties were in line with the Chinese standard for organic fertilizers (NY/T525-2021). Moreover, MOSP addition in particular enhanced the richness and diversity of bacterial communities, improving the growth of specific bacteria, such as Proteobacteria, Actinomycetes, and Planctomycetaceae, which are correlated with organic matter biodegradation at the phylum and genus levels, and inhibiting the growth of some anaerobic ammonia-oxidizing bacteria, such as Planctomycetes, at the phylum level or some denitrifying bacteria, such as Xanthomonadales and Pseudomonas, at the genus level. Overall, MOSP is more effective as an additive to produce vermicompost from cow dung vermireactors and aid in recycling organic wastes for agricultural use.