Fig. 2From: Characterization of charcoal and firewood ash for use in African peri-urban agriculturea Mean concentrations of Zn and b H2SO4-extractable K in charcoal and firewood ash from five cities in southern Ghana; bars = one standard error of mean (n = 4); different letters on top of a bar indicate a significant difference (Holm–Sidak test, P < 0.05)Back to article page