Fig. 5
Biochar cation exchange capacities (CEC) is plotted as a function of its O:C ratio (top). Biochar BET surface area is plotted against the O:C ratio in biochar (bottom). In addition to using the data from Additional file 1: Table S1; Tables 2, and 3, for biochar samples 4, 5, 6, 8, 9, 12, and 13, two additional data points with O:C ratio of 0.11 and 0.20 from our previously report (Lee et al. 2010), corresponding to corn stover chars from gasification and from pyrolysis, respectively, are also included in the plots for comparison