This study investigates the direct influence of pH on the abundance and composition of bacterial and fungal communities in arable soil. Soil samples were collected from a long-term liming experiment (pH 4.0–8.3) to minimize variations in factors other than pH. Quantitative PCR (qPCR) was used to determine the relative abundance of bacteria and fungi, while bar-coded pyrosequencing was used to analyze community composition and diversity. The results show that the relative abundance and diversity of bacteria were positively related to pH, with the latter nearly doubling between pH 4 and 8. In contrast, the relative abundance of fungi was unaffected by pH, and fungal diversity showed only a weak relationship with pH. The composition of bacterial communities was closely defined by soil pH, with variability in bacterial community composition across the 180-meter distance of the liming experiment comparable to that across soils from a wide range of biomes in North and South America. The dominance of pH in structuring bacterial communities is attributed to the narrow pH ranges for optimal growth of bacteria. In contrast, fungal community composition was less strongly affected by pH, consistent with pure culture studies showing that fungi exhibit wider pH ranges for optimal growth. The study concludes that pH has a strong influence on bacterial community composition, while the influence on fungal communities is weaker.This study investigates the direct influence of pH on the abundance and composition of bacterial and fungal communities in arable soil. Soil samples were collected from a long-term liming experiment (pH 4.0–8.3) to minimize variations in factors other than pH. Quantitative PCR (qPCR) was used to determine the relative abundance of bacteria and fungi, while bar-coded pyrosequencing was used to analyze community composition and diversity. The results show that the relative abundance and diversity of bacteria were positively related to pH, with the latter nearly doubling between pH 4 and 8. In contrast, the relative abundance of fungi was unaffected by pH, and fungal diversity showed only a weak relationship with pH. The composition of bacterial communities was closely defined by soil pH, with variability in bacterial community composition across the 180-meter distance of the liming experiment comparable to that across soils from a wide range of biomes in North and South America. The dominance of pH in structuring bacterial communities is attributed to the narrow pH ranges for optimal growth of bacteria. In contrast, fungal community composition was less strongly affected by pH, consistent with pure culture studies showing that fungi exhibit wider pH ranges for optimal growth. The study concludes that pH has a strong influence on bacterial community composition, while the influence on fungal communities is weaker.