Toxicity and accumulation of copper and nickel in maize plants cropped on calcareous and acidic field soils

Field experiments in calcareous and acidic field soils were conducted to study the effects of copper (Cu) and nickel (Ni) added to soils on maize growth and metal accumulation in maize plants. The results revealed that the critical concentrations of Cu added to soils that decreased maize grain yield by 10% (EC₁₀) were 711 mg kg^?1 for calcareous soil with a pH of 8.9, and 23 mg kg^?1 for acidic soil with a pH of 5.3. The toxicity thresholds of EC₁₀ did not differ significantly for Cu and Ni. A different pattern of Cu and Ni accumulation in maize plants was also found. The accumulation of Cu in above-ground parts of the plants increased initially as the concentrations of Cu added to soils increased, after which they decreased to a constant level. As the concentrations of Ni added to soils increased, the accumulation of Ni in stems and leaves increased linearly, but the accumulation of Ni in the grains was nonlinear. Additionally, the results revealed that Ni was transported to grains more easily than Cu. The results also showed that the concentrations of Cu and Ni in soil solutions as toxicity predictors and the critical concentrations of Cu and Ni in maize were all soil-dependent.