Fig. 6. Effect of increasing amounts of goethite application to the artificial substrate (G-0 = 0 g kg^–1; G-1 = 1 g kg^–1; G-4 = 4 g kg^–1) on shoot and root dry matter of Zea mays 32 d after planting. Means for the different treatments were separated by Tukey test. For each plant organ, means followed by the same letter were not significantly different from each other.