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 banksiana Lamb.) forest floors that received 672 kg N . ha(-1) in six applications or a single application of straw. There was no evidence of increased N availability in plots that received P and K in addition to N. Litter N concentrations were higher in N-fertilized and straw-treated plots, but rates of C mineralization and litter decomposition were not increased. Additions of N in repeated small applications or in conjunction with readily decomposable C in straw likely resulted in high retention of N in the ecosystem. The long-term increase in N availability was attributed to increased recycling of N, retention of added N in the ecosystem, and reductions in the ericaceous ground vegetation.