Quantifying the fate of nitrogen from cereal rye root and shoot biomass using N-15

Cereal rye (CR, Secale cereale, L.) is the most common cover crop species in the United States. However, despite numerous environmental benefits, the number of acres planted to CR annually remains low. Lack of adoption could be related to the dearth of knowledge on the fate of scavenged CR nitrogen. Thus, the objectives of this study were to use N-15 to track the fate of CR nitrogen amongst soil nitrogen pools, and explore CR nitrogen bioavailability over time. Our results indicated that soil type did not affect CR residue decomposition. However, 85% of shoot nitrogen and 11% of root nitrogen was released (moved from the residue to the measured soil N pools) during the incubation period demonstrating that residue type and quality plays a role in determining the dynamics of CR nitrogen release. On a whole plant basis, 14% of CR nitrogen became plant bioavailable over the course of the incubation, with the majority observed at or after 68 days of incubation. Further, at the final sampling date 53% of whole plant nitrogen remained in the organic form within the soil and 33% remained as undecomposed residues. While the majority of CR nitrogen did not enter the inorganic nitrogen pool indicating that CR provides little plant available N in the short-term, it helps elucidate some of the environmental responses observed after the adoption of CR. These results advance the knowledge of CR nitrogen fate and could aid in development of adaptive nitrogen fertilizer management strategies for producers adopting CR.