This paper presents the results of investigation of decalcification of acid sandy and loamy sand soils by infiltration waters, and potential Ca-leaching after liming treatment. For this purpose, monthly measurements were made of the concentration of CO₂ in the soil air, dissolved inorganic carbon in the soil waters, and their ionic composition. The determined dissolved inorganic carbon ranged from 5.9 to 10.6 mg dm^-3 and from 9.9 to 16.5 mg dm^-3 for the sandy and loamy sand soil, respectively. The Ca concentration in soil waters was determined as 5.9-12.4 mg dm^-3 in sandy soil and 14.2-19.8 mg dm^-3 in soil loamy sand. The calculated rate of decalcification amounted to 23.0 kg ha^-1 year^-1 in soil sandy and 19.4 kg ha^-1 year^-1 in loamy sand soil. The potential Ca-leaching is predicted as 124 kg ha^-1year^-1 for S and 87 kg ha^-1 year^-1 for loamy sand soil. At the treatment level of 3 000 kg ha^-1 4 year^-1 of CaO, ~20% of the Ca-fertilizer can be leached after the liming treatment. The results of the CO₂ concentration in the soil air may be useful in estimation of Ca-leaching from soils developed by slightly clayey sands and clayey sands in zones with a moderate climate.