Ion-selective microelectrodes and a novel micro-sampling technique were used to investigate the relationship in field soil between Brassica napus rhizoplane pH and bacterial density at a spatial scale approximating a microhabitat. Bacterial densities were observed to increase with decreasing pH, rhizoplane pH measurements varied by up to 1 pH unit over a distance of 1 mm and the mean pH of the rhizoplane at the root base varied by more than 1 pH unit between plants. These findings highlight the appropriateness of investigating the interactions between bacterial communities and their environment at the micro-spatial scale and the utility of the micro-sampling method.