Soil microorganisms are vital to many ecosystem processes, and these organisms may respond in complex ways to soil disturbances or to changes in resource availability. In semi-arid forests of the southwestern USA, water and nitrogen (N) are the two major resources that limit net primary productivity, and it has been hypothesized that tree thinning and the reintroduction of surface fire increase the availability of these resources, thus increasing plant growth. However, the impact of these treatments on soil microorganisms is largely unknown. We added water and inorganic N to thinned + burned and unmanaged ponderosa pine forests in northern Arizona, USA, to evaluate the limitation of these resources to the soil microbial biomass in each of these stand conditions. In general, during the summer dry period, both N and water appeared to be limiting to soil microorganisms in both stands, with N addition typically showing more influence than water. Both water and N additions increased soil microbial biomass and respiration. Soil enzymes showed little response to water additions, but were significantly reduced by the addition of N except in the unmanaged stand during the dry period. The onset of the summer monsoon rains reduced or eliminated most of the differences found among treatments, underscoring the importance of water in this seasonally dry environment. The similarity in the responses of the soil microbial community in both stands to added water and N suggests that these resources are still limiting to soil microbial communities following tree thinning and prescribed burning.