The carbonate-ring system and carbonate-calcium equilibrium in the water-soil system, mechanisms of formation of carbonate-calcium saturation of soil solutions and surface waters have been studied. A series of algorithms for the calculation of carbonate-calcium equilibrium, based on a joint consideration of proton and associat ion equilibrium with a step-by-step consideration of their mutual influence on each other, has been developed. Mathematical modeling of the state of the carbonate-calcium system of soil solutions has been performed, taking into account a new approach in the consideration of associat-ion and proton equilibria in the soils of southern Russia. The role and quantitative methods for predicting the behavior of the carbonate system in soils during irrigation, soil reclamation, heavy metal pollution are shown. The monograph is intended for specialists in the field of hydrochemistry, soil science, geochemistry, ecology and environmental management .