Spectral induced polarization of biochar

Biochar is considered as a soil amendment. It is made from biological material by pyrolysis, gasification or hydrothermal carbonization (HTC). Biochar may be a residual of the energetic use of plant material or particularly be produced for the use in soil. Carbonaceous material in tropical soil as found in terra preta de indio in South America is well known to improve soil properties and crop yield. Effects on soil properties in temperate climate are more complex and subject of current research. Biochar influences the biology, the chemistry and the physics of soil due to its structure, surface functional groups and redox activity.

In this project, we assess the ability of Spectral induced polarization (SIP) for detecting and monitoring the influence of biochar on some important soil physical and chemical parameters. SIP measures the frequency dependency of the complex electrical conductivity of soil in the mHz to kHz frequency range. In particular, the imaginary part of the complex electrical conductivity is strongly dependent on the type of biochar (see Figure below), whereas the real part is mainly dependent on pore water properties. We have found that the imaginary part also depends on particle size of the biochar, the amount of biochar, the chemical composition of the biochar, and the concentration of the surrounding electrolyte.

Taking into account the main features of the SIP response, the method is suitable for investigating the influence of biochar on soil water content and the fate of fertilizer (potential repository effect) as well as for detecting changes of biochar properties by disintegration or chemical modification. Therefore, we continue to investigate SIP as a minimally invasive technique to monitor the influence of biochar on important processes in soil.