IMPACTS OF SOIL-MANAGEMENT PRACTICES ON THE ORGANIC-MATTER STRUCTURE - INVESTIGATIONS BY CPMAS C-13 NMR-SPECTROSCOPY

Humus properties of 42 soil samples or humic extracts of Ap horizons o f Cambisols and Luvisols, from different field plots kept for a long t ime under continuous management conditions, have been studied by quant itative CPMAS C-13 NMR-spectroscopy. The shift range of the spectra we re divided into 8 regions, with carbon absorptions from 0-45 (aliphati cs), 45-60 (OCH3), 60-80 (CO-CN), 80-110 (anomeric carbons), 110-140 ( aryl-C), 140-160 (O-aryl-C) and 160-210 (COOH-C=O) ppm, respectively. Although soil samples and humic extracts were obtained from plots from different locations and sometimes widely differing organic carbon con tents, variances in the relative absorptions of the selected ranges we re rather small. Several absorptions were significantly correlated amo ng each other or with soil carbon and microbial contents. These correl ations were discussed with the applied management and with other resul ts about humus formation and properties. CPMAS C-13 NMR-spectroscopy a llows a reliable and comprehensive characterization of soil organic ma tter from soils without previous fractionation.