Figure 2: Effects of pH on the extraction of metals (four replicates) in biosolid-treated Romona soil (135 Mg ha−1) by 13.5 mM Ca(NO3)2 electrolyte solution and 0.01 M organic acid mixtures. The differences of metal concentrations among the pH values were tested by one-way ANOVA. Values followed by the same uppercase letter were not significantly different at . The differences of the metal concentrations between 13.5 mM Ca(NO3)2 and 0.01 M OA mixture were tested by Student-Newman-Keuls test. Values followed by the same lowercase letter were not significantly different at .