The amount of N transformed by means of nitrification is dependent on biotic and abiotic factors that include microbial community composition and soil type. Process level nutrient transformations like nitrification should be linked to the microbial community structure of keystone organisms such as ß-ammonia oxidizers. Shifts in the population of nitrifiers can result in changes in the nitrification rate. Two soils from different ecoregions, Mississippi (clay) and Illinois (clay loam), were incubated in microcosms for 150-d to determine the effect of manuring and soil type on N transformations and nitrifier community structure. Nitrification potentials determined by the shaken slurry method, 2M KCl extractable N and the community structure of ß-ammonia oxidizers measured via terminal restriction fragment length polymorphism (T-RFLP) were monitored at six time intervals. Extractable N was higher in the clay loam than in the clay. Manuring resulted in higher extractable N in the clay relative to the clay loam. Nitrification was highest in the clay on manured and unmanured treatments. Greater nitrification rates in the clay were not directly related to the quantity of extractable N. Differences in T-RFLP patterns will be compared to nitrification rates. Management strategies and soil conditions that affect ß-ammonia oxidizer populations such that nitrification is reduced can limit N losses and provide new insight into the link between process level function and microbial community structure.