¹⁵N was applied to FACE plots in pairs starting with rings 6&4 on 5/7/03, and ending with 1&2 on 5/9/03. The application used FACE site water at a rate of 250ml solution per m² ground area. A total of 0.015g N per m² ground area was applied as ¹⁵NH₄Cl (75% by mass) and K¹⁵NO₃ (25%). This raised d¹⁵N of the surface litter horizon (Oi Horizon) to 1000 per mil, a level expected to dilute rapidly as the ¹⁵N tracer travels through the system and litterfall ensues. The first ecosystem-scale measurements of ¹⁵N redistribution is scheduled for September 2003, with measurements planned through September 2006.