C and N transformations in forest soil after mounding for regeneration

Carbon and nitrogen transformations were monitored in mounded and unmounded forest soil for 3 years after mounding. The mounding was done 1 year after the clear-cutting of a Norway spruce stand where a forest fertilization ex periment had been carried out for 30 years with the following treatments: c ontrol, N fertilization, liming and combined N fertilization and liming. In the mounding plots, soil was sampled from the buried double humus layer of the mounds and from the undisturbed humus layer on the corresponding plots without soil preparation. Mounding decreased carbon mineralization in the humus layer, but had little effect on microbial biomass C and N, and net fo rmation of mineral N and nitrification. Microbial biomass and activities we re always higher in the humus layer than in the mineral soil layers. This w as observed in both the mounded and unmounded plots. Net formation of miner al N and nitrification were, however, intensive also in the mineral soil la yers of the unmounded, previously limed plots. Higher N concentrations, esp ecially NO3-N and total N, in soil solutions were found in the mounded plot s compared to the unmounded plots. The discrepancy between net formation of mineral N, nitrification and soil solution results can be explained to a g reat extent by the doubled amount of organic matter in the mounds. Mineral nitrogen concentrations of soil solution decreased during the 2 years after mounding, obviously due to the development of ground vegetation. The plant ing of birch seedlings increased microbial biomass C and carbon mineralizat ion in the mineral soil of the mounds. (C) 2000 Elsevier Science B.V. All r ights reserved.