We are interested in understanding the mechanisms by which plant-soil-microbe interactions regulate nutrient cycling and applying this knowledge to improve nutrient use efficiency in agriculture. Research plots were nested within a cover crop research project in Pennsylvania to understand how rhizosphere dynamics influence carbon and nitrogen cycling. We are using stable isotope methods in a combination of greenhouse and field experiments to address the fundamental research question: Do plants mediate their own nitrogen supply through shifts in belowground carbon allocation? By integrating greenhouse and field experiments with modeling estimates, this research links rhizosphere carbon and nitrogen cycling mechanisms to their relative importance in agroecosystem and broader biogeochemical nutrient cycles.