Soil microbes in a wheat-soybean rotation farm were studied to see how they vary in different soil depths and over time. Bacteria were most diverse near the surface, while archaea were equally diverse in all layers. The rare bacteria in the soil were linked to soil fertility. The soil bacteria and archaea were affected more by depth than by time, with different interactions happening in different layers. This shows that soil depth is more important than time in shaping the soil microbial community.