(a) p-Nitrophenyl phosphate
(b) p-Nitrophenol
(c) Iodonitrotetrazolium chloride
(d) Iodonitrotetrazolium formazan
Figure 2: Effect of biochar concentration (0, 15, 30, or 150 mg biochar soil) and biochar feedstock (straw or pine wood shavings) on the mean assay concentration or extractable concentration of enzyme assay substrates (a, c) and products (b, d), respectively, for dehydrogenase (a, b) and phosphatase (c, d) assays as applied to two different soils (Kettering or Cameroon sandy silt loams). Closed circle = straw biochar, Kettering soil; open circle = pine wood shavings biochar, Kettering soil; closed square = straw biochar, Cameroon soil; open square = pine wood shavings biochar, Cameroon soil. Bars represent SEM .