Carbon mineralization and stabilization in soils

The aim of this project is to investigate the turnover dynamics as well as mineralization and stabilization processes of soil organic carbon under different agricultural management practices. Despite our actual knowledge of soil C dynamics, which is based on numerous experiments and investigations, distinct uncertainties exist in evaluating size and turnover time of soil C pools. As a result, very few data concerning soil organic C dynamics are available for calibrating and evaluating various C models. There is only little knowledge about the mechanisms and rates of C entering into various "labile" or "active" and "recalcitrant" soil organic carbon pools. Nevertheless, the knowledge of the size and turnover rate of these C pools and the C fluxes between these pools is essential to improve existing C balance models. The long-term 14C turnover field experiment, established in 1967 in Fuchsenbigl, Lower Austria, offers the unique possibility to follow the fate of labelled C under different crop management systems (bare fallow, spring wheat, crop rotation) over a period of more than 35 years. Therefore, it should be possible to archive further essential information about C turnover rates and fluxes especially regarding to C pools with rather slow turnover rates but large pool sizes (physically stabilized or recalcitrant organic matter). The main objective of our project is to gain an advanced insight into the dynamics of slow soil organic matter pools in agricultural soils as driven by different management options. Especially the comparison of size fractions at different times after start of the two Austrian long-term experiments in combination with 14C labelling provides a realistic chance to estimate the fluxes between physically and chemically protected SOC. We will try to achieve this goal by: (i) Linking SOM pool sizes, structure and turnover, which are accessible from particle size fractions of some selected soil samples, to chemical fractionation and spectroscopic analyses of bulk soil samples without fractionation. This link between physical and chemical fractionation should essentially support our understanding of the role of humic substances in the stabilization process. (ii) Modelling of C-balances and C-dynamics to further improve existing C turnover models and to accomplish our understanding of C turnover and sequestration under different crop and soil management systems.

The aim of this project is to investigate the turnover dynamics as well as mineralization and stabilization processes of soil organic carbon under different agricultural management practices. Despite our actual knowledge of soil C dynamics, which is based on numerous experiments and investigations, distinct uncertainties exist in evaluating size and turnover time of soil C pools. As a result, very few data concerning soil organic C dynamics are available for calibrating and evaluating various C models. There is only little knowledge about the mechanisms and rates of C entering into various "labile" or "active" and "recalcitrant" soil organic carbon pools. Nevertheless, the knowledge of the size and turnover rate of these C pools and the C fluxes between these pools is essential to improve existing C balance models. The long-term 14C turnover field experiment, established in 1967 in Fuchsenbigl, Lower Austria, offers the unique possibility to follow the fate of labelled C under different crop management systems (bare fallow, spring wheat, crop rotation) over a period of more than 35 years. Therefore, it should be possible to archive further essential information about C turnover rates and fluxes especially regarding to C pools with rather slow turnover rates but large pool sizes (physically stabilized or recalcitrant organic matter). The main objective of our project is to gain an advanced insight into the dynamics of slow soil organic matter pools in agricultural soils as driven by different management options. Especially the comparison of size fractions at different times after start of the two Austrian long-term experiments in combination with 14C labelling provides a realistic chance to estimate the fluxes between physically and chemically protected SOC. We will try to achieve this goal by: 1. Linking SOM pool sizes, structure and turnover, which are accessible from particle size fractions of some selected soil samples, to chemical fractionation and spectroscopic analyses of bulk soil samples without fractionation. This link between physical and chemical fractionation should essentially support our understanding of the role of humic substances in the stabilization process. 2. Modelling of C-balances and C-dynamics to further improve existing C turnover models and to accomplish our understanding of C turnover and sequestration under different crop and soil management systems.