MICROBIAL BIOMASS-C AND BIOMASS-N IN LIMED SOIL OF NORWAY SPRUCE STANDS

The aim was to study long-term effects of liming on soil chemical prop erties and microbial biomass C and N. The study sites were twelve, 40- 80 yr old Norway spruce (Picea abies L.) stands growing on mineral soi l sites of varying fertility. Finely-ground limestone had been spread about 30 yr ago at a dose of 2 t ha-1 and reliming was carried out abo ut 20 yr later at a dose of 4 t ha-1. In both the upper and lower half of the humus layer, liming increased soil microbial biomass C, determ ined by the fumigation-extraction method. Microbial biomass C in the e luvial and illuvial layers was determined in four stands only. The dif ference between the extractable C values of fumigated and unfumigated soils, i.e. the extractable microbial biomass C, was low in these mine ral soil layers, and the validity of the results is discussed. Microbi al biomass N was determined for the humus layer of seven stands. Limin g increased microbial biomass N and its proportion of total N in both the upper and lower half of the humus layer, but the differences were not statistically significant. Liming did not change the microbial C:N ratio. Liming raised pH, and increased total and extractable Ca and M g concentrations, and total B concentration in the humus layer.