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 properties and microbial biomass C and N. The study sites were twelve, 40-80 yr old Norway spruce (Picea abies L.) stands growing on mineral soil 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 about 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, determined by the fumigation-extraction method. Microbial biomass C in the eluvial and illuvial layers was determined in four stands only. The difference between the extractable C values of fumigated and unfumigated soils, i.e. the extractable microbial biomass C, was low in these mineral soil layers, and the validity of the results is discussed. Microbial biomass N was determined for the humus layer of seven stands. Liming 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 Mg concentrations, and total B concentration in the humus layer.