Temporal Changes in Surface Properties of Sandy Haplic Podzol and Aging Biochars During Growing Season in North-Western Region of Russia

Aging of biochar in soils can result in some changes in its surface properties. The objectives of the study were to evaluate the temporal changes in: (1): the content of film water during adsorption-desorption processes on the surfaces of aging biochars and samples from topsoil of a sandy Haplic Podzol; (2) the distribution of areas of adsorption bands for oxygen-containing functional groups (OFGs) such as hydroxyl, carboxyl and phenolic on the surfaces of aging biochars. Samples of the soil and the biochar were collected from the topsoil (0-10 cm layer) in May, June and September of 2022, six years after the initial biochar application into the 0-10 cm soil layer (20 t ha-1) in 2016. A WP4-T dewpoint potentiometer was used to measure the relationships between potentials of the adsorbed film water and its content in the soil and biochar samples. An IR Fourier FSM 2202 spectrometer was applied to determine the areas of adsorption bands of OFGs on the biochar surfaces. The obtained results showed that there were non-significant differences in the mean content of adsorbed film water between the soil with and without biochars. The mean content of adsorbed film water was significantly higher (p < 0.01) in the initial biochar than in the aged biochars. The aged biochars collected at different dates of the growing season did not demonstrate any significant differences in the mean content of the adsorbed film water. According to the results obtained using IR Fourier spectroscopy, the surface of the initial biochar was characterized with the highest areas of adsorption bands of OFGs. The aged biochars showed a decrease in the areas of adsorption bands of OFGs compared to them of the initial biochar.