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

Authors: Vaughn, Steven; Kenar, James - Jim; Eller, Fred; Moser, Bryan; Jackson, Michael - Mike; Peterson, Steven - Steve

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2014
Publication Date: 12/29/2014
Publication URL: http://handle.nal.usda.gov/10113/60486
Citation: Vaughn, S.F., Kenar, J.A., Eller, F.J., Moser, B.R., Jackson, M.A., Peterson, S.C. 2015. Physical and chemical characterization of biochars produced from coppiced wood of thirteen tree species for use in horticultural substrates. Industrial Crops and Products. 66:44-51.

Interpretive Summary: Forests are a significant part of the global carbon cycle, sequestering up to 30% of the annual anthropogenic carbon dioxide emissions, approximately the same amount as all the oceans. Forest management strategies which both increase the volume of wood produced and are the most carbon-efficient should be encouraged. Coppicing is an ancient method of managing woodlands that utilizes the ability of many tree species to produce new shoots when cut near ground level. After a number of years (generally from 5-20) the coppiced tree is ready to be harvested. Trees managed in this way remain in a juvenile state, are generally more resistant to diseases, and can live for hundreds of years. Biochar is the solid, carbon-rich product resulting from the pyrolysis (thermal decomposition) of biomass in the absence of oxygen. In this study we prepared biochars from coppiced shoots of thirteen tree species found in central Illinois and compared their physical and chemical characteristics. There were slight differences among the tree species for heat production and yield of biochar, with greater differences in chemical composition, porosity, and bulk density. Our results indicate that all tree species studied would be suitable for biochar production for agricultural applications. Other factors, such as rate of growth of the coppiced shoots, need for additional fertilizer, and resistance to herbivore (deer and rabbits) browsing are equally important and can be used to determine the optimal species for a given area.

Technical Abstract: Seven-year-old coppiced shoots from thirteen species of native and non-native trees and shrubs were harvested, dried, and were 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 found to be directly proportional to surface areas. From the results of this study, while there are differences in chemical and physical structures of the biochars examined, it appears that most of these tree species would be suitable for use in horticultural substrates. Other factors such as rate of growth of the coppiced shoots, level of fertility management, and resistance to herbivore browsing are equally important and can be used to determine the optimal species for a given geographic region.