The application of phosphogypsum (PG) at rates above 10 Mg ha⁻¹ to Palexerults in western Spain had an adverse effect on wheat biomass production relative to other gypsum amendments as a result of the high Al concentration and high Al³⁺, AlOH²⁺, and Al(OH)₂ ⁺ activities in soil solution. Such effects were probably caused by F present in this byproduct. In acid media, F attacks silicates in the soil, releasing Al⁺³ At rates above 20 Mg ha⁻¹, PG had adverse effects on germination and wheat production. Even PG rates below 10 Mg ha⁻¹ could adversely affect biomass production under field conditions, especially if the amendment is not uniformly applied and, as a consequence, PG could reach much higher local concentrations.

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