Joseph, S., Discipline of Chemistry, University of Newcastle, Callaghan, NSW, Australia, School of Materials Science and Engineering, University of NSW, Sydney, NSW, Australia, Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Nanjing, China
Husson, O., CIRAD, PERSYST, UPR 115 AIDA, AfricaRice Centre, Cotonou, Benin
Graber, E.R., Institute of Soil, Water and Environmental Sciences, Volcani Center, Agricultural Research Organization, P.O. Box 6, Bet Dagan, Israel
Van Zwieten, L., NSW Department of Primary Industries, Bruxner Highway, Wollongbar, NSW, Australia, Southern Cross Plant Science, Southern Cross University, Lismore, NSW, Australia
Taherymoosavi, S., School of Materials Science and Engineering, University of NSW, Sydney, NSW, Australia
Thomas, T., School of Biotechnology and Biomolecular Sciences, University of NSW, Sydney, NSW, Australia
Nielsen, S., School of Biotechnology and Biomolecular Sciences, University of NSW, Sydney, NSW, Australia
Ye, J., School of Biotechnology and Biomolecular Sciences, University of NSW, Sydney, NSW, Australia
Pan, G., Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Nanjing, China
Chia, C., School of Materials Science and Engineering, University of NSW, Sydney, NSW, Australia
Munroe, P., School of Materials Science and Engineering, University of NSW, Sydney, NSW, Australia
Allen, J., Discipline of Chemistry, University of Newcastle, Callaghan, NSW, Australia
Lin, Y., Discipline of Chemistry, University of Newcastle, Callaghan, NSW, Australia
Fan, X., Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Nanjing, China
Donne, S., Discipline of Chemistry, University of Newcastle, Callaghan, NSW, Australia

Biochars are complex heterogeneous materials that consist of mineral phases, amorphous C, graphitic C, and labile organic molecules, many of which can be either electron donors or acceptors when placed in soil. Biochar is a reductant, but its electricaland electrochemical properties are a function of both the temperature of production and the concentration and composition of the various redox active mineral and organic phases present. When biochars are added to soils, they interact with plant roots and root hairs, micro-organisms, soil organic matter, proteins and the nutrient-rich water to form complex organo-mineral-biochar complexes Redox reactions can play an important role in the development of these complexes, and can also result in significant changes in the original C matrix. This paper reviews the redox processes that take place in soil and how they may be affected by the addition of biochar. It reviews the available literature on the redox properties of different biochars. It also reviews how biochar redox properties have been measured and presents new methods and data for determining redox properties of fresh biochars and for biochar/soil systems. © 2015 by the authors.