Nanoscale organo-mineral reactions of biochars in ferrosol: an investigation using microscopy

In this study, a chicken manure biochar (CM biochar) and a paper sludge biochar (PS biochar), prepared under similar treatment conditions, were amended into ferrosol as part of an agronomic field trial. The aim of this study is to investigate interactions between these biochars and the soil after a 3 month trial. Soil samples following field trials were taken and biochar was separated from the soil, and studied for both surface oxidation and the degree of interaction with surrounding soil by X-ray photoelectron spectroscopy (XPS), SEM and TEM equipped with EDS for elemental analysis. Following incubation in field soil, both biochars showed that soil mineral incorporation on to their surfaces occurred within the first year, although the attachment was localized at specific sites on the surface. A relatively high concentration of Al was found at the interface between the biochar and mineral phases in both aged biochars, indicating a binding role of Al. For the CM biochar, a soil-iron redox reaction may be associated with the formation of biochar-mineral complexes due to the relatively higher labile carbon content and higher pH value of this biochar. Soil mineral attachment may occur directly on to the biochar surface because of the formation of carboxylic and phenolic functional groups on the aged CM biochar surface by an oxidation reaction. For the PS biochar, adsorption of organic matter from the soil facilitated interactions between the biochar and mineral phases in the soil. Calcium is believed to be important in this process.