Two series of mixtures of a biochar with sand were investigated with spectral induced polarization (SIP) yielding the frequency dependence of the complex electrical conductivity in the range from 1 mHz to 45 kHz. The spectra of the real and the imaginary part of the complex electrical conductivity were determined for different mass fractions and particle sizes. Whereas the magnitude of the peak of the imaginary part was mainly determined by the mass fraction, the frequency of the maximum was primarily influenced by the particle size. Curves were fitted to a complex electrochemical model with reasonable accordance. The results show that biochar in sand has significant polarization and an obviously characteristic SIP response. The particle size and the fraction of biochar have an influence on the characteristics of the SIP signal. SIP might be an effective method to detect and characterize biochars in soil. The relationship between the properties of biochar and the SIP response, and the modeling methods need to be further explored
