We set out to test the hypothesis that differences in soil properties, including shifts in soil microbial community composition, resulting from long-term differences in grassland management influence the ability of soils to retain nutrients under physical stress caused by D/RW. Overall, our data show that nutrient leaching after D/RW was greatest from improved grassland soil, which had a lower microbial biomass and abundance of fungi relative to bacteria than did the unimproved grassland soil. This indicates that the composition of the microbial community in grassland soil can, in part, influence the ability of soils to retain nutrients as a result of rapid dynamic changes in soil moisture status (i.e. localized hydrological pulsing in the rhizosphere), which is common in the spring and autumn in temperate maritime climates (Turner and Haygarth, 2000). Furthermore, changes in microbial community composition, and other soil properties, resulting from land use have implications for soil nutrient leaching potential as a result of hydrological pulsing; fungal-rich soils of low-input, unimproved grasslands are better able to retain nutrients than are their improved counterparts when subjected to hydrological pulsing. More widely, our work demonstrates that soil microbial processes and microbial responses to physiological stress exert a control on soil nutrient release to leachate, and that soil microbes may thus exert an influence on water quality, that is, from an agricultural perspective, largely ignored.