Characteristics of biochar: physical and structural properties

The process parameters that are used in biochar manufacture have a signifi cant effect on its physical and structural characteristics. These characteristics, in turn, will affect biochar’s interaction with soil systems. Soils are highly complex, multi-component systems that exhibit their own distinctive physical properties. The addition of biochar to soils can thus lead to unique interactions that infl uence soil physical properties such as porosity, particle size distribution, density and packing. As a result, these combined biochar-soil properties will then impact plant yield through, for example, the availability of water and air in the vicinity of the plant root. (Other interactions, such as chemical or biological interactions, will also occur between biochar particles and soil particles, but these will not be considered in this chapter.)Whilst there have been many studies of the physical properties of biochars in anthropogenically produced soils, the pyrolysis process parameters involved are, unsurprisingly, unknown (Glaser et al, 2000; Schaefer et al,2004; Chia et al, 2012). As such, the focus of this chapter will be on the physical and structural properties of biochars derived from known feedstocks under controlled process parameters, particularly the relationship between feedstock structure, processing conditions and biochar structure.