Fig. 4. Temporal pattern of molar phosphate (P^V):arsenate (As^V) ratio in the soil solution of the root compartment with 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). In treatment G-4, the ratio could only be calculated for 3 and 10 d after planting; thereafter, P^V concentrations were close to zero. The bars, representing SD, refer to the variation between the five suction cups positioned in the root compartment.