383-4 Does Chronic N Addition Increase P Limitation in Northeastern U.S. Forest Soils?.
Overall, extractable NO3--N concentrations from the O and mineral horizons did not differ between P-fertilized and reference subplots (P = 0.961, 0.200). Extractable O NH4+-N concentrations, however, were higher (P < 0.001) in the reference than in the P-treated subplots, but no difference was detected (P = 0.139) between treatments in the mineral horizon. Sampling time influenced the P treatment effect on inorganic N similarly in both watersheds. Mean O NH4+-N concentrations in the reference subplots ranged from 0.7 to 1.5 (EB), and from 1.5 to 3.2 (WB), times higher than in the P treated subplots. The lowest difference between subplots was found two weeks (mid-June 2012), and highest difference two months (early August 2012), after treatment.
In conclusion, P-enrichment did not increase extractable inorganic N in both horizons at both sites. These results suggest that acute P additions either suppressed N mineralization, or stimulated alterative soil sinks for mineralized N. Research on microbial processes and N dynamics is underway to further define responses to P in these long-term experimental watersheds.