Development and promotion of sustainable agroecosystems necessitates that soil organic matter dynamics be better understood across different cropping systems. Cover crops have emerged as a crop management strategy to achieve agricultural sustainability and maintain environmental quality. In this project, we will be investigating how cover crop C input, soil microenvironments, and microbial community structure and function collectively foster C stabilization and control N stabilization versus losses (e.g., nitrous oxide emissions). The main objective of this proposal is to elucidate how cover crop C input controls short- and long-term C and N cycling through regulating microbial community function within soil microenvironments.

Microorganisms play a critical role in the global C and N cycles. The activities of the soil microorganisms are influenced by rhizosphere processes, which create characteristically different microenvironments than those in bulk soil. Therefore, comparing the impacts of C input from cover crop root exudation on the N processing, by the microbial community within microaggregate-microenvironments of rhizosphere soil versus the bulk soil, will shed light on the specific mechanisms governing short-term N stabilization versus losses due to C stimulation. Our global hypothesis is that cover crop growth and subsequent C and N input stimulate greater microbial cycling of N within soil microenvironments, leading to a potential increases in N stabilization coupled with decreases in N loss. The experimental framework integrates functional gene assays, specific physical soil fractionationations, and stable isotopic dilution techniques (¹⁵N) to identify and quantify microorganisms involved in N processing under cover crop systems. Fundamental knowledge of the microbial-mediated C and N cycling is vital to our understanding of overall soil organic matter dynamics in agroecosystems. Across a gradient of organic to conventional crop management, this project will look directly at the effects of cover crops on N cycling. Our approach will be the first to combine stable isotopes, physical soil fractionation, and quantitative molecular methods to reveal the precise role of microorganisms in C and N cycling within different agroecosystems. Results from this study will serve to identify sustainable farming practices for C sequestration, mitigation of increasing atmospheric N₂O emissions, and improvement of N use efficiency.

For more information contact Johan Six (jwsix@ucdavis.edu) or Angela Kong (aykong@ucdavis.edu)