Katrin Kuka

Comparison of methods for the estimation of inert carbon suitable for initialisation of the CANDY model

Almost all soil organic carbon turnover models rely on a partitioning of total organic carbon into an inert and a decomposable pool. The quantification of these pools has a large impact on modelling results. In this study several methods to estimate inert carbon in soils, based either on total soil organic matter or physical protection, were assessed with the objectives of (1) minimising errors in carbon and nitrogen dynamics and (2) ensuring usability for sites with marked differences in site conditions. CANDY simulations were carried out by varying solely the method for calculating the size of the inert carbon pool used to initialise the model. Experimental data from Bad Lauchstädt and Müncheberg were used for the simulation. The data were made available for modellers at a workshop held at Müncheberg (Germany) in 2004. The results concerning not only carbon but also nitrogen dynamics were analysed by applying selected statistical methods. It was shown that even in short-term simulations model initialisation procedure may influence the simulation results considerably. Three methods of estimating inert carbon were identified as being the most appropriate. These methods are either based on soil texture or pore-space classes and therefore account for the physical protection of soil organic matter. Thus, physical protection seems to be of major importance. By extending the scope of the investigation into nitrogen dynamics, additional support for the applicability of a selected method was obtained.

Labile water soluble components govern the short-term microbial decay of hydrochar from sewage sludge

ABSTRACT Due to higher proportions of labile carbon (C) compounds the suitability of biochar produced by hydrothermal carbonization (HTC) for C sequestration is questionable. We hypothesized that pre-treatment with water would reduce the biological decay of hydrochar from sewage sludge. Unwashed and washed feedstock and hydrochar were incubated in a short-term experiment. The kinetics of the biological decomposition of the materials was calculated on the basis of a double exponential model and the C sequestration potential using the CANDY Carbon Balance (CCB) model. Biological decomposition of the carbonized materials was governed by the percentage of labile C compounds. Mean residence time of a fast (MRTfast) and slow decay pool (MRTslow) of unwashed hydrochars varied clearly (MRTfast: 0.8 – 5.0 months and the MRTslow: 5.0–18.6 months). The pre-treatment with water removed labile hydrochar C and reduced the biological accessibility. MRTfast and MRTslow was increased by intensive washings (MRTfast: 5.0–7.4 months and the MRTslow: 14.9 months). High synthesis coefficients suggest that hydrochar C was humified and transferred into stabilized SOC. The results clearly show that once adsorbed components were eliminated, and as compared to pyrolysed biochar hydrochar from sewage sludge may also be useful for soil C sequestration.

Investigation of Pedogeophysical Relationships Using in Situ Measured Electrical Resistivity and Soil Physical and Root

Electrical resistivity tomography (ERT) is one method for mapping and monitoring of the vadose zone. However the relation between the sensed physical properties (e.g., resistivity) and the soil parameter of interest is ambiguous and often not or only poorly understood. This study was carried out to quantify soil properties and the distribution of roots in a soil profile under field conditions at different time steps during the vegetation period. In our abstract we will focus on the investigation of pedogeophysical relationships between soil physical and plant physiological properties and electrical resistivity. The relationship with soil water content varies with the time (root growth). At both time steps we find a nearly constant medium correlation of electrical resistivity and root parameters.