Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 17, 2011
Publication Date: July 3, 2012
Repository URL: http://handle.nal.usda.gov/10113/57339
Citation: Spokas, K.A., Cantrell, K.B., Novak, J.M., Archer, D.W., Ippolito, J.A., Collins, H.P., Boateng, A.A., Lima, I.M., Lamb, M.C., Mcaloon, A.J., Lentz, R.D., Nichols, K.A. 2012. Biochar: A synthesis of its agronomic impact beyond carbon sequestration. Journal of Environmental Quality. 41(4):973-989. Interpretive Summary: Elevated atmospheric carbon dioxide, potential global warming concerns and prospective use of soil as a sink for carbon has attracted interest from farmers and land managers. The potential of converting biomass into biochar (charcoal) represents one potential mechanism to reduce the atmospheric carbon dioxide levels by returning this charcoal back to the soil as a carbon sequestration benefit. Biochar has also been observed to increase soil fertility. However, the mechanisms behind these increases in soil fertility and plant growth are not fully understood. This review summarizes the current knowledge into the mechanisms and processes by which biochar impacts agricultural production. This review also summarizes the historical studies of charcoal and its use in improving crop yields. This review provides additional insight and direction in the focus of the benefits of biochar additions on agriculture, but also indicates other potentially higher value end markets for biochar that will aid in establishing an improved market which could drive the economics of biochar production. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved mechanisms of biochar additions to minimize greenhouse gas implications and improve soil carbon management.
Technical Abstract: Biochar has been recently heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity and enter into future carbon trading markets. However, scientific and economic technicalities may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties, due to the net result of production (e.g., feedstock and pyrolysis conditions) and post-production factors (storage or activation).Therefore, biochar is not a single entity, but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases following black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. However, the universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be a vital key to meeting future global food production, food security and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Despite the long research history, further research is needed to determine the specific conditions under which biochar can provide real economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.