Nitrification rates are influenced by multiple environmental drivers including ammonium (NH4+-N) availability, dissolved oxygen concentrations, water temperature, and carbon-to-nitrogen ratios. Previous work examining controls on nitrification rates in forested streams has documented seasonal variation in nitrification rates. In comparison, open-canopy agricultural streams receive excess inorganic nitrogen (N) inputs from the surrounding landscape, along with mineralization of organic rich stream sediments, and the form and timing of these N sources vary throughout the year. Yet, temporal variation in nitrification rates among seasons, and the role of environmental drivers, are not well understood for agricultural streams. We conducted seasonal nitrification assays on stream sediments to estimate nitrification rates in three agricultural streams from summer 2020 to spring 2021. We documented seasonal variation in nitrification rates and identified changes in environmental controls [e.g., stream temperature, NH4+-N and dissolved organic C (DOC) availability, and sediment chlorophyll-a] that may influence rates throughout the year. Nitrification rates were highest in spring (66.2±12.7 mg N m-2 d-1; p=0.02), which coincided with elevated NH4+-N and higher stream temperatures relative to winter (p<0.001). Nitrification rates were lowest in fall (20.2±3.5 mg N m-2 d-1) when DOC concentrations were highest (17.1±0.1 mg C L-1; p=0.01); algal senescence may allow heterotrophs to outcompete nitrifiers for available NH4+-N. In the context of previous studies, agricultural streams had elevated NH4+-N concentrations, but nitrification rates were comparable to those in less impacted systems using similar assay techniques. Rates from these agricultural streams, containing excess inorganic N and dissolved C, help extend the range of stream types where nitrification has been measured, and also provides insight into temporal variation as well as dominant controls. Although there are complex interactions among drivers and rates, understanding the dynamics of nitrification could help predict the form and timing of field- and watershed-scale N losses in agricultural landscapes.