SOIL MICROBIAL BIOMASS AND ORGANIC-MATTER COMPOSITION IN SOILS UNDER CULTIVATION

To determine whether there is a relationship between the composition of soil organic matter and the activity of the soil microbial biomass, the composition of the organic matter in 12 typical arable soils in Northwest Germany was investigated by wet chemical analysis and CPMAS cross polarization magic angle spinning C-13-NMR spectroscopy. The data were correlated with the microbial biomass as estimated by substrate-induced respiration. A strong correlation between the microbial biomass and alkylic C compounds was observed (r = -0.960***). Recalcitrant substances were enriched in this fraction, which were classified as humic acids according to the wet chemical procedure. The microbial decomposition of these humic acids is probably retarded, due to their chemical structure and/or physical bonding, when the soil microbial biomass activity is limited.