Surface Characterization of Aged Biochar Incubated in Different Types of Soil

The aim of this study was to investigate the changes that occur in the molecular form and surface morphology of aged biochar and to explore the dynamics of aging in various types of soil. For this purpose, the biochar was rice hull heated to 500 °C for 30 min. Approximately 15% of fresh biochar was incubated in either acidic red soil, weak alkaline sandy soil, or alkaline coastal solonchak for 1 and 13 months. Aged biochars incubated without soil were also prepared. The characteristics of fresh biochar and aged biochar were analyzed in terms of elemental composition, specific surface area, and pore size, together with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results for aged biochar relative to fresh biochar included: (1) decreased carbon and nitrogen contents; (2) reduced pH values which tended to be neutral; (3) reduced porosity and specific surface area (Brunauer-Emmett-Teller, BET), depending on incubation environment; and (4) increased oxygen-containing functional groups on the surface. In general, the surface characteristics of the aged biochar were changed and varied with soil type.