Effects of earthworm activities on soil nutrients and microbial diversity under different tillage measures

As a typical macrofauna in soil, earthworms alter soil structure through a series of activities, including feeding, digging, and excretion, thereby affecting farmland soil nutrients and microbial diversity. In this study, we evaluated the influence of earthworms on soil nutrient distribution and soil microbial diversity, under different tillage measures. Three cultivation methods [tillage (CT), no-tillage (NT), and no-tillage with straw (NTS)] were applied to the field. Five earthworm densities (0, 20, 50, 100, and 200 individuals/plot) were tested under each cultivation mode. Our findings showed that earthworm density improved organic C, N, and P contents in the tilled soil layer (0–30 cm). Contrastingly, in conventional tillage (CT) treatment, increases in earthworm density reduced the total N and P contents and increased the organic C content of the soil. Greater earthworm densities were associated with higher soil microbial abundances and diversities under NTS treatment, whereas the opposite effect was observed under CT treatment. Different earthworm densities also resulted in significant structural changes in the soil microbial community. Overall, these findings suggest that under the same farming method, earthworm density affects soil microorganism composition and diversity as well as soil environmental factors.