We studied effects of phosphogypsum (PG) rates ranging from 1.4 to 84.2 Mg ha-1 applied to the Ap horizon of a plinthic Palexerult on the ionic composition of the soil solution, as well as their impact on biomass production in wheat Triticum aestivum (L.), cv. Jabato. Similar soil samples were treated with highly pure gypsum (G) or the industrial byproduct red gypsum (RG) at rates equivalent to PG applications of 4.2 and 33.7 Mg ha-1 for comparison with the action of PG. All treatments increased the Ca, Mg, K, Na, and SO4 concentrations to the same extent; however, RG at high rates (30.6 Mg ha-1) raised the Na and Mg concentrations more markedly than did the other two amendments. Phosphogypsum provided the greatest increases in F, Al, and Si, the last two as a result of the corrosive effects of F on soil silicates; the increases were all proportional to the applied PG rate, and as a result, the higher PG rates increased the activities of all Al ionic species relative to G, RG, and the control. Application of G and RG at rates equivalent to PG applications of 4.2 and 33.7 Mg ha-1 increased biomass production compared with the control. Phosphogypsum increased biomass production at lower rates (0-16.8 Mg.ha-1), but biomass was virtually zero at rates above 67.3 Mg ha-1. The highest PG rates increased plant Al and F contents, the last reaching toxic levels for cattle.