(Isolation and characterization of soil organic matter fractions different in solubility as a possibility to evaluate and to improve C-pools in C-turnover models)

Abstract

Carbon-turnover models use C-pools different in stability to predict changes in soil organic matter (OBS) content due to changes in management. It is known that soil organic matter will be stabilized by different chemical and physical processes. The aim of this study is the characterisation of chemically protected and unprotected soil organic matter fractions isolated by sequential extraction and the validation of the C-pools determined by a C-turnover model with the experimentally obtained data of the isolated soil organic matter fractions. Long-term field experiments were used for this investigations as changes in soil organic matter content need more than 30 years. Soil organic matter fractions different in stability were isolated by sequential extraction, assuming that the water soluble fraction represents the unstable and the sodium pyrophosphate soluble fraction a stable part of soil organic matter. The amount of the isolated fractions were quantified and compared with the corresponding stable C-pool (HUM) simulated with the C-turnover model ROTH-C. Fourier Transform Infrared spectra of the soil organic matter fractions show that their composition is influenced by different long-term fertilization. The observed difference in soil organic matter composition is related to their sorption properties. Therefore, the isolation of the different soil organic matter fractions allows on one hand the validation of C-pools simulated with a carbon turnover model and gives on the other hand information on changes in their sorption behavior related to their composition due to changes in management.