Fig. 3

Impact of biochar application on pH, EC, CEC, TCLP-extractable Cu, and available Cu in acidic and non-acidic soils. The x-axis represents the response ratios of each indicator. The p-values for different responses are indicated by “*” and “NS” (“*” denotes 0.01 < p < 0.05; “**” denotes p < 0.01; “***” denotes p < 0.001; “NS” denotes no statistical significance, p ≥ 0.05). The Arabic numerals on the right represent the number of observations.