Stable Nitrogen Retention in Soils

We are measuring the capacity of stable soil N pools to retain N across several land-use types in Pennsylvania, including row-crop agriculture, pastures, urban lawns, and forests.

For several decades, N cycling research has focused on the relatively small pool of labile N that is made available to plants. Because labile pools are cycled rapidly by plants and soil organisms, this research conceptualized the terrestrial N cycle as driven mainly by biological processes. Weaknesses to this approach are beginning to surface, and it is becoming clear that a full understanding of terrestrial N cycle (including plant-available N) requires new research on abiotic processes and their interactions with the very large pool of (stable) soil organic N that is not immediately available to plants.

With support from the A.W. Mellon Foundation and NSF, we tested a new conceptual model for the terrestrial N cycle that explicitly includes a stable organic N pool and its dynamics. This new model unifies several currently isolated lines of N cycling research and generates testable hypotheses related to the role of microbial and abiotic incorporation of N into stable organic matter.  Our current work in this area is focused on N rentention in legacy sediments and N cycling at the Susquehanna-Shale Hills Critical Zone Observatory.