The impact of 36 years of grazing management on soil nitrogen (N) supply rate and Salix repens N status and internal cycling in dune slacks

Aims: To determine the impact of long-term rabbit and sheep grazing on Salix repens N status (green and abscised leaf N content and C:N ratio), internal N dynamics and soil N supply rate in dune slacks. Methods: Herbivore exclosures were erected in dune slacks at Ainsdale Sand Dunes NNR, creating three grazing treatments: rabbit grazing; rabbits excluded for 36 years; rabbit grazing followed by sheep and rabbit grazing for 18 years. Soil N supply rate was analysed using ion exchange membranes; leaf N dynamics of S. repens were measured over one summer. Results: Soil N supply rate was higher in ungrazed plots. There was no difference in green leaf NMASS or C:N ratio between treatments, but N dynamics differed. Adding sheep to existing rabbit grazing reduced S. repens N resorption efficiency (REFF) from 67 to 37 %; excluding rabbits had no impact. Litter NMASS was lower and C:N ratio higher in ungrazed plots. Conclusions: Grazing can impact significantly on leaf N resorption, but this impact depends on the grazing regime.