Maintaining soil health is fundamental to sustaining agricultural productivity, however, the intricate role of soil microbial diversity in this process is not fully understood. Current research acknowledges that soil microorganisms including bacteria, fungi, and archaea are pivotal in driving essential soil functions such as nutrient cycling, organic matter decomposition, and disease suppression. However, the impacts of global environmental changes and intensive agricultural practices on the diversity of these microorganisms remain a critical gap in the literature. This gap is significant because a decline in microbial diversity could severely compromise soil health, and consequently crop productivity. Here, we provide a comprehensive review of the factors influencing soil microbial diversity and examine their implications for crop performance. We assess both natural factors such as soil pH, moisture, temperature, and vegetation type as well as human-induced factors including tillage systems and fertilizer application. The review synthesizes recent findings on how these factors shape microbial communities and their functional roles in nutrient cycling, soil structure formation, and disease suppression. Our analysis highlights the mechanisms by which microbial diversity enhances plant growth and yield, addressing the gap in understanding the direct links between microbial diversity and agricultural outcomes. Our findings underscore the urgent need for sustainable agricultural practices that protect and enhance microbial diversity to safeguard long-term soil fertility and crop productivity. By addressing the challenges in manipulating soil microbial communities and integrating microbial ecology with crop management practices, this research advances our ability to sustain agricultural systems in the face of global environmental changes.