Fig. 4. The E value of Cd in the acidic soil as affected by pH and the presence of organic ligands. The fitted line is a linear regression of the pH data where E = -0.8683pH + 18.223: R² = 0.91, P > 0.001. The symbol () and error bars represent the mean value and standard deviation of triplicate measurements of pH. The other symbols represent: (0.25–5 mM) citric acid (x), (0.25–5 mM) sodium citrate (o), (0.25–1 mM) histidine (), and (0.25–1 mM) tartrate ().