Physical and chemical characterization of biochars produced from coppiced wood of thirteen tree species for use in horticultural substrates

• Biochar is the highly porous, carbon-rich residual from the pyrolysis of biomass.
• Biochars were produced from coppiced shoots of thirteen tree species.
• All of the biochars examined appeared to be suitable for horticultural applications.

Seven-year-old coppiced shoots from thirteen species of both native and non-native trees and shrubs were harvested, dried, and pyrolyzed to produce biochars for potential use in horticultural substrates. Several chemical and physical characteristics of the biochars were determined. There were slight differences among the parent coppiced shoots as to heats of combustion and biochar yields, with gray dogwood shoots having the highest values for both parameters. Surface areas, micropore surface areas, and bulk densities varied to a greater degree among the species. All biochars had very strongly basic pH values (>9.0), although electrical conductivity values varied greatly, appearing to correlate with levels of potassium found in the biochars. Ash content of the biochars was similar, and using the guidelines for O/C, H/C, and surface area, all biochar samples meet standards for utilization as soil amendments. Peak moisture sorption of the biochars was directly proportional to surface areas. From the results of this study, while there were differences in chemical and physical structures of the biochars examined, most of these tree species would be suitable for use in horticultural applications. Other factors such as, rate of growth of the coppiced shoots, level of fertility management, and resistance to herbivore browsing are important as well and can be used to determine the optimal species for a given geographic region.