Numerous studies have evaluated the safe and beneficial use of biosolids on farmland. However, there has been limited interest to incorporate a high pH and Ca (calcium) rich material such as lime stabilized (LS) biosolids into alkaline calcareous soils that are common in arid regions. Increasing soil alkalinity and salinity may reduce soil productivity, despite the incorporation of organic matter. The objective of this study was to evaluate the impacts of excess Ca introduced from biosolids and/or irrigation water on the pH and salinity of moderately alkaline calcareous soils. In Experiment 1, either anaerobically-digested (AN) or LS biosolids were incorporated into a loamy sand at rates of 0 and 2%; packed into soil columns; and irrigated with water containing 0, 820, or 1,640 mg of Ca as calcium chloride. In Experiment 2, LS biosolids at loading rates of 0, 25 and 50 Mg/ha on soil pH and Ca soil phases were analyzed under replicated field conditions. Soluble, exchangeable, and residual calcium were evaluated. Soil pH and salinity (measured as electrical conductivity) were determined using a 1:1 soil to water extract. In Experiments 1and 2, soluble rather than exchangeable Ca was inversely correlated with soil pH and contributed to soil salinity. Soil pH was expressed as; pH = 6.8571 - 0.4569 log(soluble Ca); (r²=0.577), where (soluble Ca) denotes Ca activity determined from the extended Debye-Huckel equation. Increases in soluble Ca were associated with reductions in soil pH. We hypothesize that Ca²⁺ introduced into alkaline soils increases CaCO₃ formation and H⁺ concentrations. As a consequence, soil pH is reduced. Increases in soil CO₂ and HCO₃^- concentrations from organic mineralization may also promote CaCO₃ precipitation. Our results suggest that the application of LS biosolids to alkaline soils may be beneficial and will not increase soil alkalinity.