LONG-TERM EFFECTS OF REPEATED N FERTILIZATION AND STRAW APPLICATION IN A JACK PINE FOREST .3. NITROGEN AVAILABILITY IN THE FOREST FLOOR

A long-term increase in N availability was evident in higher rates of net N mineralization and lower C/N ratios in jack pine (Pinus banksian a Lamb.) forest floors that received 672 kg N . ha(-1) in six applicat ions or a single application of straw. There was no evidence of increa sed N availability in plots that received P and K in addition to N. Li tter N concentrations were higher in N-fertilized and straw-treated pl ots, but rates of C mineralization and litter decomposition were not i ncreased. Additions of N in repeated small applications or in conjunct ion with readily decomposable C in straw likely resulted in high reten tion of N in the ecosystem. The long-term increase in N availability w as attributed to increased recycling of N, retention of added N in the ecosystem, and reductions in the ericaceous ground vegetation.