The reclamation of saline soils requires the application of amendments such as gypsum and organic matter. The effects of gypsum and sulfur inoculated with Acidithiobacillus applied individually for the alleviation of saline soils is recognized, but the effects of mixed proportions of these products, especially on plant parameters, have not been studied. The aim of this study was to evaluate the effects of gypsum (G) and sulfur inoculated with Acidithiobacillus (S*) at various rates and mixing proportions, S*:G, on the alleviation of soil salinity. A control treatment that did not receive amendment was included, but the seeds did not germinate in this treatment. The effect of PK rock biofertilizer in interaction with the amendment treatments was also observed in cowpeas. The seeds were inoculated with effective Bradyrhizobium strains. At 45 days of growth, the cowpea shoot dry weight (DW) and the nutrient uptake in the shoots (total N, Na, P and K) were determined in the plants, and the soil was analyzed for pH, exchangeable Na, and available P and K. The results indicate that sulfur inoculated with Acidithiobacillus reduced soil pH, especially when applied without gypsum. The biofertilizer effectively increased the shoot biomass and nutrient uptake and increased the available P and K in the amended soil, and the best results were observed when the biofertilizer was used in interaction with S* and G in a mixing proportion equivalent to 50:50. In saline soil with high pH, PK rock biofertilizer seems to be an important factor for improving soil quality and may be an alternative to P and K fertilization.