The majority of N transformations in the soil are
biologically mediated processes. Physical and chemical processes related to soil
type also affect the rate of N transformations such as nitrification and
ammonia volatilization. Ammonium and ammonia held on exchange sites or fixed by
clays can reduce ammonia volatilization and nitrification rates by influencing
substrate availability. Different species of nitrifiers have varying
nitrification rates and ability to scavenge NH4+. Our
research was designed to determine the effect of soil type on NH4+
transformations and availability to nitrifiers. The availability of NH4+
is expected to influence the dynamics and structure of nitrifier communities.
Soil samples were collected at USDA-ARS sites across a variety of ecoregions
and soil types. Each soil series was used in a 30 d incubation containing a
dairy slurry (300 kg N ha-1) amended soil and a soil control. Sub
samples were removed at 5 time intervals for analyses of nitrification potentials
and community structure of beta-ammonia oxidizers via terminal restriction
fragment length polymorphism. Separating out the effect of microbial community
structure and soil type on N transformations will improve our understanding of
nutrient cycling, as well as, bridge the gap between soil chemistry and
microbiology.